54491044
Arctic Ocean outflow shelves in the changing Arctic: A review and perspectives
Published version. Source at http://doi.org/10.1016/j.pocean.2015.08.007 . License in accordance with the journal's policy - CC-BY-NC-ND .
129932624
Food webs and physical–biological coupling on pan-Arctic shelves: Unifying concepts and comprehensive perspectives ☆
Perhaps more than in any other ocean, our understanding of the continental shelves of the Arctic Mediterranean is decidedly disciplinary, regional and fractured, and this shortcoming must be addressed if we are to face and prepare for climate change. A fundamental flaw is that while excellent process studies exist, and while recent ship-based expeditions have added greatly to our collective body of knowledge, an integrated and fully pan-Arctic perspective on the structure and function of food webs on Arctic shelves is lacking. Based on the collective overviews given in Progress in Oceanography xx, xx–xx, we attempt to address this issue. To build a perspective that inter-connects the various shelf regions we suggest three unifying typologies affecting food webs that will hopefully allow inter-comparison of regional investigations. The first is for shelf geography, wherein shelves are classified according to their role in the Arctic throughflow. The second is for ice climate, wherein the various ice regimes are examined for their specific impacts on food web dynamics. The third is for stratification where it is argued that the source of buoyancy, thermal or haline, impacts production and the vertical carbon flux. We then address the connection between physical habitat and biota on pan-Arctic (and global climate) scales. This discussion begins with the recognition that the Arctic Ocean is integral to the World Ocean via its thermohaline (“estuarine”) exchanges with the Atlantic and Pacific. As such the Arctic and its shelves act as a double estuary, wherein incoming waters become both lighter (positive estuary), by mixing with freshwater sources, and heavier (negative estuary) by cooling and brine release. Shelves are central to such transformations. This complex interconnectivity coupling of the Arctic Ocean to its sub-Arctic (and more productive) neighbors demands that food webs be considered through a macroecological view that includes an ecology of advection. We argue that the macroecological view is required if we are to understand and model food webs under forcing along climate gradients. To aid this effort we introduce the concept of contiguous domains, wherein physical habitats are joined by common features that will allow inter-comparisons of existing and future food webs over large scales and climatic gradients. Finally, we speculate on the range of possible futures for Arctic shelves based on the palaeo-record.
128957062
The great salinity anomaly in the northern North Atlantic 1968-1982
The widespread freshening of the upper 500–800m layer of the northern North Atlantic, which this paper describes, represents one of the most persistent and extreme variations in global ocean climate yet observed in this century. 
 
Though a range of explanations have been advanced to explain this event, including in situ changes in the surface moisture flux, this paper describes the Great Salinity Anomaly as largely (though not entirely) an advective event, traceable around the Atlantic subpolar gyre for over 14 years from its origins north of Iceland in the mid-to-late 1960s until its return to the Greenland Sea in 1981–1982. The overall propagation speed around this subpolar gyre is estimated at about 3cm s−1. Of the total salt deficit associated with the anomaly as it passed south along the Labrador Coast in 1971–1973 (about 72 × 109 tonnes), a deficit equivalent to about two thirds of this figure (47 × 109 tonnes) ultimately passed through the Faroe-Shetland Channel to the Barents Sea, Arctic Ocean and Greenland Sea during the mid-1970s. 
 
Possible effects on deep water formation and on the representativeness of historical section data are discussed.
36017668
Dilution of the Northern North Atlantic Ocean in Recent Decades
Declining salinities signify that large amounts of fresh water have been added to the northern North Atlantic Ocean since the mid-1960s. We estimate that the Nordic Seas and Subpolar Basins were diluted by an extra 19,000 ± 5000 cubic kilometers of freshwater input between 1965 and 1995. Fully half of that additional fresh water—about 10,000 cubic kilometers—infiltrated the system in the late 1960s at an approximate rate of 2000 cubic kilometers per year. Patterns of freshwater accumulation observed in the Nordic Seas suggest a century time scale to reach freshening thresholds critical to that portion of the Atlantic meridional overturning circulation.
131050190
Thermohaline circulation in the Arctic Mediterranean Seas
The renewal of the deep North Atlantic by the various overflows of the Greenland-Scotland ridges is only one manifestation of the convective and mixing processes which occur in the various basins and shelf areas to the north: the Arctic Ocean and the Greenland, Iceland, and Norwegian seas, collectively called the Arctic Mediterranean. The traditional site of deep ventilation for these basins is the Greenland Sea, but a growing body of evidence also points to the Arctic Ocean as a major source of deep water. This deep water is relatively warm and saline, and it appears to be a mixture of dense, brine-enriched shelf water with intermediate strata in the Arctic Ocean. The deep water exits the Arctic Ocean along the Greenland slope to mix with the Greenland Sea deep water. Conversely, very cold low-salinity deep water from the Greenland Sea enters the Arctic Ocean west of Spitsbergen. Within the Arctic Ocean, the Lomonosov Ridge excludes the Greenland Sea deep water from the Canadian Basin, leaving the latter warm, saline, and rich in silica. In general, the entire deep-water sphere of the Arctic Mediterranean is constrained by the Greenland-Scotland ridges to circulate internally. Therefore it is certain of the intermediate waters formed in the Greenland and Iceland seas which ventilate the North Atlantic. These waters have a very short residence time in their formation areas and are therefore able to rapidly transmit surface-induced signals into the deep North Atlantic.
128591413
Simulated interannual variability of the Greenland Sea deep water formation and its connection to surface forcing
A fully prognostic Arctic ice-ocean model is used to study the interannual variability of deepwater formation in the Greenland Sea gyre based on the simulations for the Arctic ice-ocean system for the period 1955 and 1960–1985. The model uses monthly climatology for thermodynamic forcing components (such as air temperature and cloudiness), together with constant annual net precipitation and river runoff. The daily wind forcing is derived from analyzed sea level air pressures from the National Center for Atmospheric Research. In summary, the model shows that the occurrence of deep convection in the Greenland Sea gyre is controlled by the extensive Fram Strait ice export and/or local wind conditions in the Greenland Sea. In the latter case the weakening of the local wind curl allows the Polar Front to move eastward. The movement of the Polar Front causes adverse ice conditions, often together with much larger than normal ice export from the Arctic, such as in 1968, which can block convection in the gyre. The density difference between upper and lower layers is investigated as an indication of water mass formation through convection, occurring as strong diffusion in the model. The model-simulated density difference between the average top 100 m and deep levels reveals that the period 1960–1985 had only a few distinct years with weak stratification, and, especially, the model predicts no deep convection since the mid-1970s. The common factor for the years of the weakest stratification is extreme wintertime wind events. Deep convection is also evident as a decrease of the model-predicted heat content of the upper 2000 m which can, to a high degree, be explained by local heat loss. The salt content changes in the Greenland gyre are independent of the heat content changes and are determined by the advection of fresh or salty anomalies, either from the Arctic or from the frontal movement. The model indicates that the surface salinity flux favors freshening, even in wintertime, so that brine rejection is less important in buoyancy loss than heat loss in leading to deep convection. The model shows that the system has a memory; deep convection in one year will precondition the following year.
130643008
A Simulation of Thermohaline Effects of a Great Salinity Anomaly
Abstract Model simulations of an idealistic “Great Salinity Anomaly” (GSA) demonstrate that variability in the sea ice export from the Arctic when concentrated to short pulses can have a large influence on the meridional heat transport and can lead to an altered overturning state. One single freshwater disturbance resulting from excess ice export, as in 1968, can disrupt the deep mixing process. The critical condition for a large oceanic response is defined by the intensity, duration, and timing of the ice pulse, in particular, as it exits through the Denmark Strait. A recovery from this event takes several years for advection and diffusion to remove the salinity anomaly. Concurrently, the influence of the GSA propagates to the subtropics via the boundary currents and baroclinic adjustment. As a result of this adjustment, there are large (up to 20%) changes in the strength of the overturning cell and in the meridional heat transport in the subtropics and subpolar areas. Simulations show a temperature–sali...
14153450
The Role of Ice-Ocean Interactions in the Variability of the North Atlantic Thermohaline Circulation
The simulated influence of Arctic sea ice on the variability of the North Atlantic climate is discussed in the context of a global coupled ice‐ocean‐atmosphere model. This coupled system incorporates a general circulation ocean model, an atmospheric energy moisture balance model, and a dynamic‐thermodynamic sea ice model. Under steady seasonal forcing, an equilibrium solution is obtained with very little variability. To induce variability in the model, daily varying stochastic anomalies are applied to the wind forcing of the Northern Hemisphere sea ice cover. These stochastic anomalies have observed spatial patterns but are random in time. Model simulations are run for 1000 yr from an equilibrium state and the variability in the system is analyzed. The sensitivity of the system to the ice‐ocean coupling of both heat and freshwater is also examined. Under the stochastic forcing conditions, the thermohaline circulation (THC) responds with variability that is approximately 10% of the mean. This variability has enhanced spectral power at interdecadal timescales that is concentrated at approximately 20 yr. It is forced by fluctuations in the export of ice from the Arctic into the North Atlantic. Substantial changes in sea surface temperature and salinity are related to changes in the overturning circulation and the sea ice coverage in the northern North Atlantic. Additionally, the THC variability influences the Arctic Basin through heat transport under the ice pack. Results from sensitivity studies suggest that the freshwater exchange from the variable ice cover is the dominant process for forcing variability in the overturning. The simulated Arctic ice export appears to provide stochastic forcing to the northern North Atlantic that excites a damped oscillatory ocean-only mode. The insulating capacity of the variable sea ice has a negligible effect on the THC. Ice‐ocean thermal coupling acts to damp THC variability, causing an approximately 25% reduction in the THC standard deviation.
38747458
Causes and impacts of changes in the Arctic freshwater budget during the twentieth and twenty-first centuries in an AOGCM
The fourth version of the atmosphere-ocean general circulation (AOGCM) model developed at the Institut Pierre-Simon Laplace (IPSL-CM4) is used to investigate the mechanisms influencing the Arctic freshwater balance in response to anthropogenic greenhouse gas forcing. The freshwater influence on the interannual variability of deep winter oceanic convection in the Nordic Seas is also studied on the basis of correlation and regression analyses of detrended variables. The model shows that the Fram Strait outflow, which is an important source of freshwater for the northern North Atlantic, experiences a rapid and strong transition from a weak state toward a relatively strong state during 1990–2010. The authors propose that this climate shift is triggered by the retreat of sea ice in the Barents Sea during the late twentieth century. This sea ice reduction initiates a positive feedback in the atmosphere-sea ice-ocean system that alters both the atmospheric and oceanic circulations in the Greenland-Iceland-Norwegian (GIN)-Barents Seas sector. Around year 2080, the model predicts a second transition threshold beyond which the Fram Strait outflow is restored toward its original weak value. The long-term freshening of the GIN Seas is invoked to explain this rapid transition. It is further found that the mechanism of interannual changes in deep mixing differ fundamentally between the twentieth and twenty-first centuries. This difference is caused by the dominant influence of freshwater over the twenty-first century. In the GIN Seas, the interannual changes in the liquid freshwater export out of the Arctic Ocean through Fram Strait combined with the interannual changes in the liquid freshwater import from the North Atlantic are shown to have a major influence in driving the interannual variability of the deep convection during the twenty-first century. South of Iceland, the other region of deep water renewal in the model, changes in freshwater import from the North Atlantic constitute the dominant forcing of deep convection on interannual time scales over the twenty-first century.
55707709
Outflow of Arctic Ocean Sea Ice into the Greenland and Barents Seas: 1979-2007
Abstract Twenty-nine years of Arctic sea ice outflow into the Greenland and Barents Seas are summarized. Outflow is computed at three passages: Fram Strait, between Svalbard and Franz Josef Land (S–FJL), and between Franz Josef Land and Severnaya Zemlya (FJL–SZ). Ice drift at the flux gates has been reprocessed using a consistent and updated time series of passive microwave brightness temperature and ice concentration (IC) fields. Over the record, the mean annual area outflow at the Fram Strait is 706(113) × 103 km2; it was highest in 1994/95 (1002 × 103 km2) when the North Atlantic Oscillation (NAO) index was near its 29-yr peak. The strength of the “Transpolar Drift Stream” (TDS) was high during the late 1980s through the mid-1990s. There is no statistically significant trend in the Fram Strait area flux. Even though there is a positive trend in the gradient of cross-strait sea level pressure, the outflow has not increased because of a negative trend in IC. Seasonally, the area outflow during recent sum...
129445545
Accelerated decline in the Arctic sea ice cover
[1] Satellite data reveal unusually low Arctic sea ice coverage during the summer of 2007, caused in part by anomalously high temperatures and southerly winds. The extent and area of the ice cover reached minima on 14 September 2007 at 4.1 × 106 km2 and 3.6 × 106 km2, respectively. These are 24% and 27% lower than the previous record lows, both reached on 21 September 2005, and 37% and 38% less than the climatological averages. Acceleration in the decline is evident as the extent and area trends of the entire ice cover (seasonal and perennial ice) have shifted from about −2.2 and −3.0% per decade in 1979–1996 to about −10.1 and −10.7% per decade in the last 10 years. The latter trends are now comparable to the high negative trends of −10.2 and −11.4% per decade for the perennial ice extent and area, 1979–2007.
133730527
Distribution and trends in Arctic sea ice age through spring 2011
[1] Analysis of a satellite-derived record of sea ice age for 1980 through March 2011 shows continued net decrease in multiyear ice coverage in the Arctic Ocean, with particularly extensive loss of the oldest ice types. The fraction of total ice extent made up of multiyear sea ice in March decreased from about 75% in the mid 1980s to 45% in 2011, while the proportion of the oldest ice declined from 50% of the multiyear ice pack to 10%. These losses in the oldest ice now extend into the central Arctic Ocean and adjacent to the Canadian Archipelago; areas where the ice cover was relatively stable prior to 2007 and where long-term survival of sea ice through summer is considered to be most likely. Following record-minimum multiyear ice coverage in summer 2008, the total multiyear ice extent has increased to amounts consistent with the negative trend from 2001–2006, with an increasing proportion of older ice types. This implies some ability for the ice pack to recover from extreme conditions. This recovery has been weakest in the Beaufort Sea and Canada Basin though, with multiyear ice coverage decreasing by 83% from 2002 to 2009 in the Canada Basin, and with more multiyear ice extent now lost in the Pacific sector than elsewhere in the Arctic Ocean.
128541961
On the 2012 record low Arctic sea ice cover: Combined impact of preconditioning and an August storm
[1] A new record low Arctic sea ice extent for the satellite era, 3.4 × 106 km2, was reached on 13 September 2012; and a new record low sea ice area, 3.0 × 106 km2, was reached on the same date. Preconditioning through decades of overall ice reductions made the ice pack more vulnerable to a strong storm that entered the central Arctic in early August 2012. The storm caused the separation of an expanse of 0.4 × 106 km2 of ice that melted in total, while its removal left the main pack more exposed to wind and waves, facilitating the main pack's further decay. Future summer storms could lead to a further acceleration of the decline in the Arctic sea ice cover and should be carefully monitored.
55435653
Summer sea ice motion from the 18 GHz channel of AMSR‐E and the exchange of sea ice between the Pacific and Atlantic sectors
[1] We demonstrate that sea ice motion in summer can be derived reliably from the 18GHz channel of the AMSR-E instrument on the EOS Aqua platform. The improved spatial resolution of this channel with its lower sensitivity to atmospheric moisture seems to have alleviated various issues that have plagued summer motion retrievals from shorter wavelength observations. Two spatial filters improve retrieval quality: one reduces some of the microwave signatures associated with synoptic-scale weather systems and the other removes outliers. Compared with daily buoy drifts, uncertainties in motion are ∼3–4 km/day. Using the daily motion fields, we examine five years of summer ice area exchange between the Pacific and Atlantic sectors of the Arctic Ocean. With the sea-level pressure patterns during the summer of 2006 and 2007 favoring the export of sea ice into the Atlantic Sector, the regional outflow is ∼21% and ∼15% of the total sea ice retreat in the Pacific sector.
53336452
Summer retreat of Arctic sea ice: Role of summer winds
[1] The unprecedented retreat of first-year ice during summer 2007 was enhanced by strong poleward drift over the western Arctic induced by anomalously high sea-level pressure (SLP) over the Beaufort Sea that persisted throughout much of the summer. Comparison of the tracks of drifting buoys with monthly mean SLP charts shows a substantial Ekman drift. By means of linear regression analysis it is shown that Ekman drift during summer has played an important role in regulating annual minimum Arctic sea-ice extent in prior years as well. In combination, the preconditioning by events in prior years, as represented by an index of May multi-year ice, and current atmospheric conditions, as represented by an index of July–August–September SLP anomalies over the Arctic basin account for ∼60% of the year-to-year variance of September sea-ice extent since 1979.
17424774
Rapid reduction of Arctic perennial sea ice
[1] The extent of Arctic perennial sea ice, the year-round ice cover, was significantly reduced between March 2005 and March 2007 by 1.08 x 10 6 km 2 , a 23% loss from 4.69 × 10 6 km 2 to 3.61 × 10 6 km 2 , as observed by the QuikSCAT/SeaWinds satellite scatterometer (QSCAT). Moreover, the buoy-based Drift-Age Model (DM) provided long-term trends in Arctic sea-ice age since the 1950s. Perennial-ice extent loss in March within the DM domain was noticeable after the 1960s, and the loss became more rapid in the 2000s when QSCAT observations were available to verify the model results. QSCAT data also revealed mechanisms contributing to the perennial-ice extent loss: ice compression toward the western Arctic, ice loading into the Transpolar Drift (TD) together with an acceleration of the TD carrying excessive ice out of Fram Strait, and ice export to Baffin Bay. Dynamic and thermodynamic effects appear to be combining to expedite the loss of perennial sea ice.
129788065
Changes in Arctic sea ice result in increasing light transmittance and absorption
[1] Arctic sea ice has declined and become thinner and younger (more seasonal) during the last decade. One consequence of this is that the surface energy budget of the Arctic Ocean is changing. While the role of surface albedo has been studied intensively, it is still widely unknown how much light penetrates through sea ice into the upper ocean, affecting sea-ice mass balance, ecosystems, and geochemical processes. Here we present the first large-scale under-ice light measurements, operating spectral radiometers on a remotely operated vehicle (ROV) under Arctic sea ice in summer. This data set is used to produce an Arctic-wide map of light distribution under summer sea ice. Our results show that transmittance through first-year ice (FYI, 0.11) was almost three times larger than through multi-year ice (MYI, 0.04), and that this is mostly caused by the larger melt-pond coverage of FYI (42 vs. 23%). Also energy absorption was 50% larger in FYI than in MYI. Thus, a continuation of the observed sea-ice changes will increase the amount of light penetrating into the Arctic Ocean, enhancing sea-ice melt and affecting sea-ice and upper-ocean ecosystems.
43804616
Surface freshening in the Arctic Ocean's Eurasian Basin: An apparent consequence of recent change in the wind-driven circulation
[1] Data collected by an autonomous ice-based observatory that drifted into the Eurasian Basin between April and November 2010 indicate that the upper ocean was appreciably fresher than in 2007 and 2008. Sea ice and snowmelt over the course of the 2010 drift amounted to an input of less than 0.5 m of liquid freshwater to the ocean (comparable to the freshening by melting estimated for those previous years), while the observed change in upper-ocean salinity over the melt period implies a freshwater gain of about 0.7 m. Results of a wind-driven ocean model corroborate the observations of freshening and suggest that unusually fresh surface waters observed in parts of the Eurasian Basin in 2010 may have been due to the spreading of anomalously fresh water previously residing in the Beaufort Gyre. This flux is likely associated with a 2009 shift in the large-scale atmospheric circulation to a significant reduction in strength of the anticyclonic Beaufort Gyre and the Transpolar Drift Stream.
4366728
Changing Arctic Ocean freshwater pathways
Freshening in the Canada basin of the Arctic Ocean began in the 1990s and continued to at least the end of 2008. By then, the Arctic Ocean might have gained four times as much fresh water as comprised the Great Salinity Anomalyof the 1970s, raising the spectre of slowing global ocean circulation. Freshening has been attributed to increased sea ice melting and contributions from runoff, but a leading explanation has been a strengthening of the Beaufort High—a characteristic peak in sea level atmospheric pressure—which tends to accelerate an anticyclonic (clockwise) wind pattern causing convergence of fresh surface water. Limited observations have made this explanation difficult to verify, and observations of increasing freshwater content under a weakened Beaufort High suggest that other factors must be affecting freshwater content. Here we use observations to show that during a time of record reductions in ice extent from 2005 to 2008, the dominant freshwater content changes were an increase in the Canada basin balanced by a decrease in the Eurasian basin. Observations are drawn from satellite data (sea surface height and ocean-bottom pressure) and in situ data. The freshwater changes were due to a cyclonic (anticlockwise) shift in the ocean pathway of Eurasian runoff forced by strengthening of the west-to-east Northern Hemisphere atmospheric circulation characterized by an increased Arctic Oscillation index. Our results confirm that runoff is an important influence on the Arctic Ocean and establish that the spatial and temporal manifestations of the runoff pathways are modulated by the Arctic Oscillation, rather than the strength of the wind-driven Beaufort Gyre circulation.
54964528
Pacific Ocean inflow: Influence on catastrophic reduction of sea ice cover in the Arctic Ocean
Received 27 December 2005; revised 7 March 2006; accepted 13 March 2006; published 21 April 2006. [1] The spatial pattern of recent ice reduction in the Arctic Ocean is similar to the distribution of warm Pacific Summer Water (PSW) that interflows the upper portion of halocline in the southern Canada Basin. Increases in PSW temperature in the basin are also well-correlated with the onset of sea-ice reduction that began in the late 1990s. However, increases in PSW temperature in the basin do not correlate with the temperature of upstream source water in the northeastern Bering Sea, suggesting that there is another mechanism which controls these concurrent changes in ice cover and upper ocean temperature. We propose a feedback mechanism whereby the delayed sea-ice formation in early winter, which began in 1997/1998, reduced internal ice stresses and thus allowed a more efficient coupling of anticyclonic wind forcing to the upper ocean. This, in turn, increased the flux of warm PSW into the basin and caused the catastrophic changes. Citation: Shimada, K., T. Kamoshida, M. Itoh, S. Nishino, E. Carmack, F. A. McLaughlin, S. Zimmermann, and A. Proshutinsky (2006), Pacific Ocean inflow: Influence on catastrophic reduction of sea ice cover in the Arctic Ocean, Geophys. Res. Lett., 33, L08605,
12841025
Observed increases in Bering Strait oceanic fluxes from the Pacific to the Arctic from 2001 to 2011 and their impacts on the Arctic Ocean water column
[1] Mooring data indicate the Bering Strait throughflow increases ∼50% from 2001 (∼0.7 Sv) to 2011 (∼1.1 Sv), driving heat and freshwater flux increases. Increase in the Pacific-Arctic pressure-head explains two-thirds of the change, the rest being attributable to weaker local winds. The 2011 heat flux (∼5 × 1020J) approaches the previous record high (2007) due to transport increases and warmer lower layer (LL) temperatures, despite surface temperature (SST) cooling. In the last decade, warmer LL waters arrive earlier (1.6 ± 1.1 days/yr), though winds and SST are typical for recent decades. Maximum summer salinities, likely set in the Bering Sea, remain remarkably constant (∼33.1 psu) over the decade, elucidating the stable salinity of the western Arctic cold halocline. Despite this, freshwater flux variability (strongly driven by transport) exceeds variability in other Arctic freshwater sources. Remote data (winds, SST) prove insufficient for quantifying variability, indicating interannual change can still only be assessed by in situ year-round measurements.
206522735
Smallest Algae Thrive As the Arctic Ocean Freshens
In the Arctic Ocean, phytoplankton cell sizes have decreased with warming temperatures and fresher surface waters. As climate changes and the upper Arctic Ocean receives more heat and fresh water, it becomes more difficult for mixing processes to deliver nutrients from depth to the surface for phytoplankton growth. Competitive advantage will presumably accrue to small cells because they are more effective in acquiring nutrients and less susceptible to gravitational settling than large cells. Since 2004, we have discerned an increase in the smallest algae and bacteria along with a concomitant decrease in somewhat larger algae. If this trend toward a community of smaller cells is sustained, it may lead to reduced biological production at higher trophic levels.
31933552
Massive Phytoplankton Blooms Under Arctic Sea Ice
In midsummer, diatoms have taken advantage of thinning ice cover to feed in nutrient-rich waters. Phytoplankton blooms over Arctic Ocean continental shelves are thought to be restricted to waters free of sea ice. Here, we document a massive phytoplankton bloom beneath fully consolidated pack ice far from the ice edge in the Chukchi Sea, where light transmission has increased in recent decades because of thinning ice cover and proliferation of melt ponds. The bloom was characterized by high diatom biomass and rates of growth and primary production. Evidence suggests that under-ice phytoplankton blooms may be more widespread over nutrient-rich Arctic continental shelves and that satellite-based estimates of annual primary production in these waters may be underestimated by up to 10-fold.
206545871
Export of Algal Biomass from the Melting Arctic Sea Ice
Diatom Fall 2012 saw the greatest Arctic ice minimum ever recorded. This allowed unprecedented access for research vessels deep into the Arctic Ocean to make high-latitude observations of ice melt and associated phenomena. From the RV Polarstern between 84° to 89° North, Boetius et al. (p. 1430, published online 14 February; see the cover) observed large-scale algal aggregates of the diatom Melosira arctica hanging beneath multiyear and seasonal ice across a wide range of latitudes. The strands of algae were readily dislodged and formed aggregates on the seabed up to 4400 meters below, where the algae are consumed by large mobile invertebrates, such as sea cucumbers and brittle stars. Although Nansen observed sub-ice algae in the Arctic 100 years ago, the extent of this bloom phenomenon was unknown. The dynamics of such blooms must impinge on global carbon budgets, but how the dynamics will change as ice melt becomes more extensive remains unclear. As polar ice retreated in 2012, it left evidence of large algal deposits in its wake. In the Arctic, under-ice primary production is limited to summer months and is restricted not only by ice thickness and snow cover but also by the stratification of the water column, which constrains nutrient supply for algal growth. Research Vessel Polarstern visited the ice-covered eastern-central basins between 82° to 89°N and 30° to 130°E in summer 2012, when Arctic sea ice declined to a record minimum. During this cruise, we observed a widespread deposition of ice algal biomass of on average 9 grams of carbon per square meter to the deep-sea floor of the central Arctic basins. Data from this cruise will contribute to assessing the effect of current climate change on Arctic productivity, biodiversity, and ecological function.
53355515
Seasonal and interannual variability of downwelling in the Beaufort Sea
[1] In this paper, we examine the seasonal and interannual to decadal variability of oceanic downwelling in the Beaufort Sea. The surface wind stress is the primary driver for variability in the upper Arctic Ocean and sea ice. The seasonal variability of the surface wind over the western Arctic is strongly influenced by a high sea level pressure center that emerges in the fall and diminishes in the summer. The wind stress and sea ice velocity are both anticyclonic from fall to spring and thus force an upwelling along the Alaskan and Canadian coast and downwelling in the interior Beaufort Sea. The upwelling and downwelling varied significantly on the interannual to decadal time scales from 1979 to 2006. There was no significant correlation between the upwelling/downwelling rate in the Beaufort Sea and the Arctic Oscillation index over this 28 year period. The coastal upwelling and interior downwelling in the Beaufort Sea had gradually intensified from 1979 to 2006. This change was almost entirely due to the increase in sea ice velocity according to three additional sensitivity calculations. The anticyclonic ice velocity over the western Arctic Ocean accelerated in the 28 year period, and the acceleration was not driven solely by the wind stress. The geostrophic wind condition was actually similar between 1979–1986 and 1997–2004. However, the ice velocity was much greater in the latter period. We hypothesize that the change in ice dynamics (thinner and less areal coverage) was responsible for the change of ice velocity.
36435454
Increasing River Discharge to the Arctic Ocean
Synthesis of river-monitoring data reveals that the average annual discharge of fresh water from the six largest Eurasian rivers to the Arctic Ocean increased by 7% from 1936 to 1999. The average annual rate of increase was 2.0 ± 0.7 cubic kilometers per year. Consequently, average annual discharge from the six rivers is now about 128 cubic kilometers per year greater than it was when routine measurements of discharge began. Discharge was correlated with changes in both the North Atlantic Oscillation and global mean surface air temperature. The observed large-scale change in freshwater flux has potentially important implications for ocean circulation and climate.
396075
CryoSat-2 estimates of Arctic sea ice thickness and volume
[1] Satellite records show a decline in ice extent over more than three decades, with a record minimum in September 2012. Results from the Pan-Arctic Ice-Ocean Modelling and Assimilation system (PIOMAS) suggest that the decline in extent has been accompanied by a decline in volume, but this has not been confirmed by data. Using new data from the European Space Agency CryoSat-2 (CS-2) mission, validated with in situ data, we generate estimates of ice volume for the winters of 2010/11 and 2011/12. We compare these data with current estimates from PIOMAS and earlier (2003–8) estimates from the National Aeronautics and Space Administration ICESat mission. Between the ICESat and CryoSat-2 periods, the autumn volume declined by 4291 km3 and the winter volume by 1479 km3. This exceeds the decline in ice volume in the central Arctic from the PIOMAS model of 2644 km3 in the autumn, but is less than the 2091 km3 in winter, between the two time periods.
129491826
Thinning of Arctic sea ice observed in Fram Strait: 1990–2011
[1] Time series (1990–2011) of sea ice thickness observed by moored sonars in the Transpolar Drift in Fram Strait are examined. Contrasting the post-2007 years against the 1990s, three remarkable changes in the monthly ice thickness distributions are highlighted: (1) The thickness of old level ice (modal thickness) is reduced by 32%, (2) the old ice modal peak width is reduced by 25%, and (3) the fraction of (ridged) ice thicker than 5 m is reduced by 50%. The combined effect on the mean ice thickness is a reduction from an annual average of 3.0 m during the 1990s to 2.2 m during 2008–2011. Most of the thinning took place after 2005–2006. While the old ice modal thickness and peak width show signs of recovery after 2008, the decreasing trend in fraction of ridged ice and mean ice thickness persists until the end of the record in 2011. The ice observed in Fram Strait carries an integrated signal of Arctic change due to the advection of ice from many sites in the Arctic. Based on concurrence in timing, we conclude that much of the thinning quantified here is reflecting recent change in the age composition of the Arctic ice cover toward younger ice. The old level ice remains thin, and as such the ice cover remains preconditioned for new summers of very low sea ice extent.
128465867
Monitoring ice thickness in Fram Strait
Time series of ice thickness in Fram Strait are evaluated together with ice drift for estimation of the ice flux from the Arctic Ocean. Ice draft was measured from moored sonars every 4 min, suggesting a nominal sampling interval of 30 m. On the basis of these data the annual cycle of many statistics can be resolved. The modal ice thickness shows a maximum of 3.15 m in May and a minimum in September of 2.43 m, indicating an annual variation range of 0.72 m. This compares with model results, comprehensive drillings, and most of the submarine observations during the last 2-3 decades, indicating no significant long-term ice thickness change. This is also concurrent with the lack of significant temperature changes in the Arctic Ocean during the same period. The mean ice thickness in the central core of the ice stream shows an annual amplitude of 1 m with a minimum in September of 2.25 m and a maximum in April-May of 3.25 m. The mean thickness of ice only (open water excluded) is 3.27 m and compares with 3.29 m which is the mean thickness of ice only from 17 submarine tracks in the Arctic Ocean 1960-1982. The mean annual ice export, which is equal to the mean annual net production of ice in the Arctic Ocean, is ∼2850 km 3 yr -1 for the period 1990-1996. This efflux shows significant variations from year to year with a minimum in 1990-1991 of ∼2050 km 3 yr -1 and a maximum in 1994-1995 of ∼4700 km 3 yr -1 . This significant variation of nearly 130% is mainly caused by an increased atmospheric forcing and to a lesser degree by an increase in the annual mean ice thickness of ∼20% over the same period.
129442322
Characteristics of colored dissolved organic matter (CDOM) in the Arctic outflow in the Fram Strait: Assessing the changes and fate of terrigenous CDOM in the Arctic Ocean
Absorption coefficients of colored dissolved organic matter (CDOM) were measured together with salinity, delta O-18, and inorganic nutrients across the Fram Strait. A pronounced CDOM absorption maximum between 30 and 120 m depth was associated with river and sea ice brine enriched water, characteristic of the Arctic mixed layer and upper halocline waters in the East Greenland Current (EGC). The lowest CDOM concentrations were found in the Atlantic inflow. We show that the salinity-CDOM relationship is not suitable for evaluating conservative mixing of CDOM. The strong correlation between meteoric water and CDOM is indicative of the riverine/terrigenous origin of CDOM in the EGC. Based on CDOM absorption in Polar Water and comparison with an Arctic river discharge weighted mean, we estimate that a 49-59% integrated loss of CDOM absorption across 250-600 nm has occurred. A preferential removal of absorption at longer wavelengths reflects the loss of high molecular weight material. In contrast, CDOM fluxes through the Fram Strait using September velocity fields from a high-resolution ocean-sea ice model indicate that the net southward transport of terrigenous CDOM through the Fram Strait equals up to 50% of the total riverine CDOM input; this suggests that the Fram Strait export is a major sink of CDOM. These contrasting results indicate that we have to constrain the (C)DOM budgets for the Arctic Ocean much better and examine uncertainties related to using tracers to assess conservative mixing in polar waters. Citation: Granskog, M. A., C. A. Stedmon, P. A. Dodd, R. M. W. Amon, A. K. Pavlov, L. de Steur, and E. Hansen (2012), Characteristics of colored dissolved organic matter (CDOM) in the Arctic outflow in the Fram Strait: Assessing the changes and fate of terrigenous CDOM in the Arctic Ocean, J. Geophys. Res., 117, C12021, doi:10.1029/2012JC008075.
129560355
Monitoring the volume, freshwater and heat fluxes passing through Lancaster sound in the Canadian arctic archipelago
Abstract A research project, consisting of instrumentation development and mooring work, has monitored the volume, heat and freshwater fluxes passing through Lancaster Sound, one of the three main pathways through the Canadian Arctic Archipelago. Instrumentation to measure the current direction of the Acoustic Doppler Current Profilers (ADCPs) moored in this region of low horizontal magnetic field strength have been successfully developed and implemented. Time series data from August 1998 to September 2001 of the salinity, temperature and velocity fields and the derived estimates of the volume, freshwater and heat fluxes passing through Lancaster Sound are reported. The fluxes exhibit large seasonal and interannual variabilities. Fluxes are small in fall and winter and reach their maxima in late summer. The seasonal eastward volume flux estimate ranged from a low of ‐0.01 Sv in the fall of 1998 to a maximum of 1.3 Sv in the summer of 2000. Its three‐year mean of 0.75 Sv varies interannually by ±0.25 Sv. Freshwater flux estimates vary similarly with minima in winter and maxima in late summer. They generally are one‐fifteenth of the volume fluxes; but are likely underestimated as their surface freshwater content is based on data from Conductivity‐Temperature‐Depth (CTD) sensors at 25–30 m depth thus missing fresher water above the summer halocline. The pack ice contribution to the freshwater flux is small as most of the year the pack ice is land‐fast; it accounts for less than 5% of the freshwater flux when spread over the entire year.
129282488
Wind‐forcing of volume transport through Lancaster Sound
[1] Volume and freshwater transport through Lancaster Sound are estimated from mooring measurements collected in eastern Barrow Strait for 13 years between 1998 and 2011. Estimates from 2006 to 2011 confirm the relationship between surface wind and volume transport derived from data collected between 1998 and 2006. Volume transport through Barrow Strait along the Northwest Passage is significantly correlated with northeastward winds in the Beaufort Sea, parallel to the western coasts of the Canadian Arctic Archipelago, at monthly to interannual time scales. The location and wind direction for which there is maximum correlation are consistent with the flow being driven by a sea level difference between opposite ends of the Passage, and the difference being determined by setup caused by alongshore winds in the Beaufort Sea. Monthly alongshore wind anomalies account for 43% of the variance of the transport anomalies (p 0.05). The annual cycles of the total volume transport and its part attributed to the Beaufort Sea wind both have peaks in the summer and are lowest in the autumn. Correlations of the volume transport anomaly with ice velocity anomalies are lower than with surface wind anomalies.
131237287
Accurate Ocean Current Direction Measurements Near the Magnetic Poles
Ocean current direction measurements through the Canadian archipelago have required development of a strategy that uses specialised instrumentation to cope with the small horizontal component of the earth's magnetic field in this region. Subsurface instrumented moorings collecting bihourly data through yearlong deployments, use precision heading reference systems to measure the orientation of Acoustic Doppler Current Profilers mounted in streamlined buoyancy packages. Current directions are then corrected for the significant fluctuations in magnetic declination occurring near the magnetic pole, using data from a nearby geomagnetic observatory. Concurrent observations of current speed and direction from independent moored measurement systems are shown to be in good agreement.
108031696
An Energy Conserving Oceanographic Profiler For Use Under Mobile Ice Cover; ICYCLER
ICYCLER is a moored oceanographic profiler designed to measure surface layer water properties under mobile ice cover. The profiler can provide daily 50 meter salinity-temperature-chlorophyll profiles for a full year. Data are collected during each profiling ascent with an instrumented float that avoids ice impact using an onboard echo sounder. Once measurements are acquired, the sensors are hauled back down to an ice-free depth. An efficient energy-conserving mechanical design minimizes power requirements to allow for a logistically manageable and hydrodynamically efficient package. An ICYCLER prototype was successfully used the Canadian Arctic Archipelago for a year-long deployment and a second re-designed ICYCLER is being tested for Arctic deployment in the summer of 2004.
52268507
Long-term Trends in the Population Ecology of Polar Bears in Western Hudson Bay in Relation to Climatic Change
From 1981 through 1998, the condition of adult male and female polar bears has declined significantly in western Hudson Bay, as have natality and the proportion of yearling cubs caught during the open water period that were independent at the time of capture. Over this same period, the breakup of the sea ice on western Hudson Bay has been occurring earlier. There was a significant positive relationship between the time of breakup and the condition of adult females (i.e., the earlier the breakup, the poorer the condition of the bears). The trend toward earlier breakup was also correlated with rising spring air temperatures over the study area from 1950 to 1990. We suggest that the proximate cause of the decline in physical and reproductive parameters of polar bears in western Hudson Bay over the last 19 years has been a trend toward earlier breakup, which has caused the bears to come ashore in progressively poorer condition. The ultimate factor responsible for the earlier breakup in western Hudson Bay appears to be a long-term warming trend in April-June atmospheric temperatures.
52949627
Historical Analysis of Sea Ice Conditions in M'Clintock Channel and the Gulf of Boothia, Nunavut : Implications for Ringed Seal and Polar Bear Habitat
Sea ice is an integral part of the marine ecosystem in the Arctic and important habitat for ringed seals and polar bears. To study changes in sea ice characteristics indicative of ringed seal habitat (and linked, through predator/prey relationships, to polar bear habitat), we examined historical changes in sea ice concentration and type within M'Clintock Channel and the Gulf of Boothia, two regions of the Canadian Arctic Archipelago, during 1980-2000. Results suggest large interannual variability in winter ice conditions over the 21-year study period. In M'Clintock Channel, first-year ice types dominated consistently, while in the Gulf of Boothia, thick ice types dominated in some years. For breakup and consolidation, the regional spatial patterns differed significantly, occurring in opposite directions (N-S vs. S-N) in the two regions. The dates showed considerable interannual variability in both regions, suggesting no clear pattern of either earlier breakup or later consolidation. Analysis of satellite data confirmed the results obtained from digital ice charts. Ringed seal habitat suitability indices (HSI) indicate that both regions contained primary, secondary, and tertiary HSI classes. No trends were evident in the secondary or tertiary classes, but changes in the primary class were evident in M'Clintock Channel over the five-year period 1997-2001. Dynamic and thermodynamic sea ice processes are important to ringed seal habitat (and ultimately, polar bear habitat) at regional and hemispheric scales in the current context of climate variability and change.
52949690
Trends in the Dates of Ice Freeze-up and Breakup over Hudson Bay, Canada
Hudson Bay experiences a complete cryogenic cycle each year. Sea ice begins to form in late October, and the Bay is usually ice-free in early August. This seasonally varying ice cover plays an important role in the regional climate. To identify secular trends in the cryogenic cycle, we examined variability in the timing of sea-ice formation and retreat during the period 1971– 2003. The dates of ice freeze-up and breakup at 36 locations across Hudson Bay were catalogued for each year from weekly ice charts provided by the Canadian Ice Service. We used the nonparametric Mann-Kendall test to determine the statistical significance of the trends and the Theil-Sen approach to estimate their magnitude. Our results indicate statistically significant trends toward earlier breakup in James Bay, along the southern shore of Hudson Bay, and in the western half of Hudson Bay, and toward later freeze-up in the northern and northeastern regions of Hudson Bay. These trends in the annual ice cycle of Hudson Bay coincide with both the regional temperature record and the projections from general circulation models. If this trend toward a longer ice-free season continues, Hudson Bay will soon face important environmental challenges.
128676778
Multi‐year sea‐ice conditions in the western Canadian arctic archipelago region of the northwest passage: 1968–2006
Abstract Numerous studies have reported decreases in Arctic sea‐ice cover over the past several decades and General Circulation Model (GCM) simulations continue to predict future decreases. These decreases — particularly in thick perennial or multi‐year ice (MYI) — have led to considerable speculation about a more accessible Northwest Passage (NWP) as a transit route through the Canadian Arctic Archipelago (CAA). The Canadian Ice Service Digital Archive (CISDA) is used to investigate dynamic import/export and in situ growth of MYI within the western CAA regions of the NWP from 1968 to 2006. This analysis finds that MYI conditions in the western CAA regions of the NWP have remained relatively stable because the M'Clintock Channel and Franklin regions continuously operate as a drain‐trap mechanism for MYI. Results also show that in addition to the Queen Elizabeth Islands (QEI) region, the Western Parry Channel and the M'Clintock Channel are also regions where a considerable amount of MYI forms in situ and combined with dynamic imports contributes to heavy MYI conditions. There is also evidence to suggest that more frequent dynamic import of MYI appears to have occurred since‐1999 compared to the formation of more MYI in situ before 1999. As a result, the drain‐trap mechanism that has historically maintained heavy MYI conditions in the NWP is perhaps operating faster now than it was in the past. Based on the 38‐year MYI record examined in this study, it is likely that the mechanisms operating within the western CAA regions of the NWP can facilitate the continued presence of MYI for quite some time.
128812930
Climate change and ice hazards in the Beaufort Sea
Recent reductions in the summer extent of sea ice have focused the world’s attention on the effects of climate change. Increased CO2-derived global warming is rapidly shrinking the Arctic multi-year ice pack. This shift in ice regimes allows for increasing development opportunities for large oil and gas deposits known to occur throughout the Arctic. Here we show that hazardous ice features remain a threat to stationary and mobile infrastructure in the southern Beaufort Sea. With the opening up of the ice pack, forecasting of high-frequency oscillations or local eddy-driven ice motion will be a much more complex task than modeling average ice circulation. Given the observed reduction in sea ice extent and thickness this rather counterintuitive situation, associated with a warming climate, poses significant hazards to Arctic marine oil and gas development and marine transportation. Accurate forecasting of hazardous ice motion will require improved real-time surface wind and ocean current forecast models capable of ingesting local satellite-derived wind data and/or local, closely-spaced networks of anemometers and improved methods of determining high-frequency components of surface ocean current fields ‘up-stream’ from drilling and extraction operations.
55579045
Freshwater fluxes in the East Greenland Current: A decade of observations
[1] Over a decade of mooring measurements in the western Fram Strait at 78°50′N shows that the annual mean liquid freshwater flux (FWF) in the East Greenland Current is relatively constant at −1274 ± 453 km3 yr−1 (−40.4 ± 14.4 mSv) despite the fact that the annual mean total volume transport of the EGC has more than doubled since 2001. This is shown to be due to an increase of the transport in the deeper ocean and the fact that the largest FW content is present on the East Greenland shelf and not in the core of the EGC. In order to capture the FWF on the shelf modeling results of NAOSIM are included showing that a mean contribution of FWF on the shelf of at least −807 ± 357 km3 yr−1 (−25.6 ± 11.3 mSv) should be added to the FWF obtained for the EGC. When compared to the extra input of freshwater required to account for the 1960–1990 freshening of the northern North Atlantic, the observed variations in the 1998–2008 EGC liquid freshwater fluxes are small.
55567678
Direct measurements of volume transports through Fram Strait
Heat and freshwater transports through Fram Strait are understood to have a significant influence on the hydrographic conditions in the Arctic Ocean and on water mass modifications in the Nordic seas. To determine these transports and their variability reliable estimates of the volume transport through the strait are required. Current meter moorings were deployed in Fram Strait from September 1997 to September 1999 in the framework of the EU MAST III Variability of Exchanges in the Northern Seas programme. The monthly mean velocity fields reveal marked velocity variations over seasonal and annual time scales, and the spatial structure of the northward flowing West Spitsbergen Current and the southward East Greenland Current with a maximum in spring and a minimum in summer. The volume transport obtained by averaging the monthly means over two years amounts to 9.5 ± 1.4 Sv to the north and 11.1 ± 1.7 Sv to the south (1 Sv = 106 m3s-1). The West Spitsbergen Current has a strong barotropic and a weaker baroclinic component; in the East Greenland Current barotropic and baroclinic components are of similar magnitude. The net transport through the strait is 4.2 ± 2.3 Sv to the south. The obtained northward and southward transports are significantly larger than earlier estimates in the literature; however, within its range of uncertainty the balance obtained from a two year average is consistent with earlier estimates.
129173923
Arctic warming through the Fram Strait: Oceanic heat transport from 3 years of measurements
We present estimates of volume and heat transport through Fram Strait for the period 1997 to 2000 from data of moored instruments. Full depth volume transports at 78° 55'N were in the order of 10 Sv both northwards and southwards with an annual mean net transport between 2 and 4 Sv to the south. The temperature of the northward flow of Atlantic Water had a strong seasonality with a minimum in winter. Nevertheless, the northward heat transport was highest in winter caused by the winter maximum of northward volume transport. During the three years of observation, the heat transport in the West Spitsbergen Current increased from 28 to 46 TW as a result of both increased speed and temperature. In contrast to the West Spitsbergen Current, the volume and heat transport of East Greenland Current remained fairly constant. An integration over a subsection of the East Greenland Current showed similar values of volume transport to that obtained by measurements in the 1980s (Foldvik et al., 1988). The southward heat transport through modified Atlantic Water weakened slightly between 1997 and 1999 despite increased temperatures.
126733179
Exchanges of Freshwater through the Shallow Straits of the North American Arctic
The shallow straits of the North American Arctic include Bering Strait, which connects the Pacific Ocean to the Arctic Ocean, and the myriad channels of the Canadian Arctic Archipelago, which connect the Arctic Ocean to the Atlantic. A net flux of freshwater passes from the North Pacific into the North Atlantic via these straits (plus Fram Strait), and thereby stabilizes a global imbalance in precipitation less evaporation between the two major ocean basins [0, 2]. At the same time, the fluctuating outflows of fresh Arctic waters into the Greenland Sea, via Fram Strait, and into the Labrador Sea, via the Canadian Arctic Archipelago, may control the occurrence of deep ocean convection in these areas [3, 4, 5, 6]. For these reasons, the freshwater fluxes through the shallow straits of the North American Arctic are important within the global climate system.
55661414
Oxygen isotope ratio, barium and salinity in waters around the North American coast from the Pacific to the Atlantic: Implications for freshwater sources to the Arctic throughflow
K. Falkner acknowledges funding from the US National Science Foundation (OPP 
Award 0230354).
131694738
The role of sea ice and other fresh water in the Arctic circulation
Salinity stratification is critical to the vertical circulation of the high-latitude ocean. We here examine the control of the vertical circulation in the northern seas, and the potential for altering it, by considering the budgets and storage of fresh water in the Arctic Ocean and in the convective regions to the south. We find that the present-day Greenland and Iceland seas, and probably also the Labrador Sea, are rather delicately poised with respect to their ability to sustain convection. Small variations in the fresh water supplied to the convective gyres from the Arctic Ocean via the East Greenland Current can alter or stop the convection in what may be a modern analog to the halocline catastrophes proposed for the distant past. The North Atlantic salinity anomaly of the 1960s and 1970s is a recent example; it must have had its origin in an increased fresh water discharge from the Arctic Ocean. Similarly, the freshening and cooling of the deep North Atlantic in recent years is a likely manifestation of the increased transfer of fresh water from the Arctic Ocean into the convective gyres. Finally, we note that because of the temperature dependence of compressibility, a slight salinity stratification in the convective gyres is required to efficiently ventilate the deep ocean.
100844686
Primary and Secondary Production in the Arctic Seas
Marine bio-production in the Arctic and Subarctic is based primarily on microscopic unicellular algae (phytoplankton) in the water column and micro-algae associated with ice. Algae utilise light to produce organic matter by photosynthesis, thereby reducing CO2 while releasing O2 and producing carbohydrates which, according to the needs of the algae, can be converted into essential compounds such as proteins and nucleic acids by incorporating nitrogen, phosphorus, sulphur, and other elements.
128487155
Volume, Freshwater, and Heat Fluxes through Davis Strait, 2004–05*
Abstract Davis Strait volume [−2.3 ± 0.7 Sv (1 Sv ≡ 106 m3 s−1); negative sign indicates southward transport], freshwater (−116 ± 41 mSv), and heat (20 ± 9 TW) fluxes estimated from objectively mapped 2004–05 moored array data do not differ significantly from values based on a 1987–90 array but are distributed differently across the strait. The 2004–05 array provided the first year-long measurements in the upper 100 m and over the shelves. The upper 100 m accounts for 39% (−0.9 Sv) of the net volume and 59% (−69 mSv) of the net freshwater fluxes. Shelf contributions are small: 0.4 Sv (volume), 15 mSv (freshwater), and 3 TW (heat) from the West Greenland shelf and −0.1 Sv, −7 mSv, and 1 TW from the Baffin Island shelf. Contemporaneous measurements of the Baffin Bay inflows and outflows indicate that volume and freshwater budgets balance to within 26% and 4%, respectively, of the net Davis Strait outflow. Davis Strait volume and freshwater fluxes nearly equal those from Fram Strait, indicating that both are...
128486988
Fram Strait sea ice volume export estimated between 2003 and 2008 from satellite data
[1] Satellite-based estimates of monthly sea ice volume exports through Fram Strait for the years 2003 to 2008 are presented. These are obtained from individual satellite observations of sea ice thickness, area, and drift. First, sea ice freeboard is inferred from ICESat laser altimeter observations and then converted to ice thickness estimates. Sea ice area and drift are derived from AMSR-E 89 GHz data. Retrieved sea ice thickness estimates compare within 0.5 m with the few ULS data available in the Fram Strait. The mean, minimum, and maximum observed monthly Fram Strait sea ice volume export amounts to 217, 92, and 420 km3/month, respectively. In comparison to former Fram Strait sea ice volume export estimates obtained during the 1990s our estimates are slightly smaller (−33 km3/month) but are within the natural variability and no significant change of the total amount of Fram Strait sea ice export can be observed.
54769606
Fram Strait sea ice outflow
[1] We summarize 24 years (1978–2002) of ice export estimates and examine, over a 9-year record, the associated variability in the time-varying upward-looking sonar (ULS) thickness distributions of the Fram Strait. A more thorough assessment of the PMW (passive microwave) ice motion with 5 years of synthetic aperture radar (SAR) observations shows the uncertainties to be consistent with that found by Kwok and Rothrock [1999], giving greater confidence to the record of ice flux calculations. Interesting details of the cross-strait motion profiles and ice cover characteristics revealed by high-resolution SAR imagery are discussed. The average annual ice area flux over the period is 866,000 km2/yr. Between the 1980s and 1990s, the decadal difference in the net exported ice area is ∼400,000 km2, approximately half the annual average. Except for the years with extreme negative NAO, correlation of winter ice area export with the NAO index remains high (R2 = 0.62). With thickness estimates from ULS moorings, we estimate the average annual ice volume flux (8 years) to be ∼2218 km3/yr (∼0.07 Sv). Over the ∼9-year ULS ice thickness data set, there is an overall decrease of 0.45 m in the mean ice thickness over the entire time series and a decrease of 0.23 m over the winter months (December through March). Correspondingly, the mode of the MY ice thickness exhibits an overall decrease of 0.55 m and a winter decrease of 0.42 m. These are significant trends. Whether these trends are indicative of the thickness trends of the Arctic Ocean is examined, as the time-varying behavior of the monthly ULS thickness distributions can be related not only to the seasonal cycle in the basal growth and melt, but also to the magnitude and pattern of ice motion in the Arctic Ocean, and the proximity of the ULS moorings to the ice edge.
56064450
Sea ice velocity in the Fram Strait monitored by moored instruments
[1] The Fram Strait sea ice velocity was measured by means of a new method using moored Doppler Current Meters in the period 1996–2000. Almost 3 years of ice velocity observations near 79°N 5°W are analyzed. The average southward ice velocity was 0.16 m/s. The correlation between the ice velocity and the cross-strait sea level pressure (SLP) difference was R = 0.76 for daily means and R = 0.79 for monthly means. The same cross-strait SLP difference exhibits a positive trend since 1950 of 10% of the mean per decade. By a simple linear model we compute mean sea ice area flux to 850 000 km2/year for the period 1950–2000. Ice thickness, monitored by means of Upward Looking Sonars since 1990, is also discussed. The combined data gave a monthly ice volume flux of 200 km3 during the last decade with no significant trend.
127437144
Constraints on Estimating Mass, Heat and Freshwater Transports in the Arctic Ocean: An Exercise
The ASOF programme, with its study of the transports between the Arctic Ocean and the North Atlantic via the subarctic seas – the Nordic Seas, Baffin Bay and the Labrador Sea –, also provides an opportunity to examine the mass (volume), freshwater and heat budgets of the Arctic Ocean. The exchanges between the two passages between the Arctic Ocean and the Nordic Seas, Fram Strait and the Barents Sea opening between Norway and Bear Island, have been measured continuously since 1997, first in the VEINS programme (Variability of Exchanges in the Northern Seas) and then in ASOF and the observations are presently continued within the DAMOCLES (Developing Arctic Modelling and Observing Capabilities for Longterm Environmental Studies) programme. The transports through two of the three main channels in the Canadian Arctic Archipelago, the Lancaster Sound and the Jones Sound, have been directly measured for a couple of years now (Prinsenberg and Hamilton 2005), and the instruments from the first year-long measurements in Nares Strait have been brought in. The fluxes through Bering Strait have also been studied intensely the last 10–15 years (e.g. Woodgate and Aagaard 2005). The work within ASOF has shown that the transports through Fram Strait and through the Canadian Arctic Archipelago are those most difficult to determine. The Archipelago because of the severe climate, the remoteness of the area and the nearby location of the magnetic North Pole, Fram Strait because of its depth, the transports in both directions, and the presence of baroclinic and barotropic eddies leading to high spatial and temporal variability. The estimates of the mean transport through Bering Strait obtained since the mid-1980s have ranged around 0.8 Sv (1 × 10 m s), but large seasonal variations have been reported, 1.2 Sv in summer and 0.4 Sv in winter (Coachman and Aagaard 1988; Woodgate and Aagaard 2005). The mean transport of Atlantic water to the Arctic Ocean through the Barents Sea opening has been estimated to 1.5 Sv from
55118914
Recirculation in the Fram Strait and transports of water in and north of the Fram Strait derived from CTD data
Abstract. The volume, heat and freshwater transports in the Fram Strait are estimated from geostrophic computations based on summer hydrographic data from 1984, 1997, 2002 and 2004. In these years, in addition to the usually sampled section along 79° N, a section between Greenland and Svalbard was sampled further north. Quasi-closed boxes bounded by the two sections and Greenland and Svalbard can then be formed. Applying conservation constraints on these boxes provides barotropic reference velocities. The net volume flux is southward and varies between 2 and 4 Sv. The recirculation of Atlantic water is about 2 Sv. Heat is lost to the atmosphere and the heat loss from the area between the sections averaged over the four years is about 10 TW. The net heat (temperature) transport is 20 TW northward into the Arctic Ocean, with large interannual differences. The mean net freshwater added between the sections is 40 mSv and the mean freshwater transport southward across 79° N is less than 60 mSv, indicating that most of the liquid freshwater leaving the Arctic Ocean through Fram Strait in summer is derived from sea ice melt in the northern vicinity of the strait. In 1997, 2001 and 2003 meridional sections along 0° longitude were sampled and in 2003 two smaller boxes can be formed, and the recirculation of Atlantic water in the strait is estimated by geostrophic computations and continuity constraints. The recirculation is weaker close to 80° N than close to 78° N, indicating that the recirculation is mainly confined to the south of 80° N. This is supported by the observations in 1997 and 2001, when only the northern part of the meridional section, from 79° N to 80° N, can be computed with the constraints applied. The recirculation is found strongest close to 79° N.
128870840
The freshwater composition of the Fram Strait outflow derived from a decade of tracer measurements
The composition of the Fram Strait freshwater outflow is investigated by comparing 10 sections of concurrent salinity, ?18O, nitrate and phosphate measurements collected between 1997 and 2011. The largest inventories of net sea ice meltwater are found in 2009, 2010 and 2011. The 2009–2011 sections are also the first to show positive fractions of sea ice meltwater at the surface near the core of the EGC. Sections from September 2009–2011 show an increased input of sea ice meltwater at the surface relative to older September sections. This suggests that more sea ice now melts back into the surface in late summer than previously. Comparison of April, July and September sections reveals seasonal variations in the inventory of positive sea ice meltwater, with maximum inventories in September sections. The time series of sections reveals a strong anti-correlation between meteoric water and net sea ice meltwater inventories, suggesting that meteoric water and brine may be delivered to Fram Strait together from a common source. We find that the freshwater outflow at Fram Strait exhibits a similar meteoric water to net sea ice meltwater ratio as the central Arctic Ocean and Siberian shelves, suggesting that much of the sea ice meltwater and meteoric water at Fram Strait may originate from these regions. However, we also find that the ratio of meteoric water to sea ice meltwater inventories at Fram Strait is decreasing with time, due to an increased surface input of sea ice meltwater in recent sections.
129194733
Mixing and transports in Barrow Strait, the central part of the Northwest passage
* Abstract- Recent hydrographic and current meter data (1981-1983) from Barrow Strait, the central part of the Northwest Passage, are used to determine water mass mixing and long-term mass and heat transports. As surface water moves from the Arctic Ocean to Baffin Bay it loses heat and gains salt in the winter from the growing ice cover. Salty and warmer subsurface water is mixed into the surface layer to various degrees before entering Barrow Strait where three surface water masses of Arctic origin can be identified. The volume transport leaving the Arctic Ocean via Barrow Strait has an annual mean of 0.5 x 10 6 m 3 s -1 and varies seasonally from a minimum of 0.2 x 10 6 m
128648826
The Canadian Arctic Archipelago throughflow in a multiresolution global model: Model assessment and the driving mechanism of interannual variability
[1] The volume and freshwater transports through the Canadian Arctic Archipelago (CAA) are assessed using the unstructured-mesh Finite Element Sea ice-Ocean Model (FESOM) in a global setup with the CAA resolved at 5 km scale. The hindcast simulation realistically represents fluxes through the main gates of the Arctic Ocean and the Arctic sea ice conditions. During the period 1968–2007, the mean volume transports through Lancaster Sound and Nares Strait amount to 0.86 and 0.91 Sv, respectively. The monthly mean volume transport through western Lancaster Sound is highly correlated with the observational estimate (r = 0.81). The seasonal variability of the Lancaster Sound transport is well represented in the model. The simulated mean CAA freshwater export rate is 123 mSv, slightly higher than the observational estimate. The interannual variability of CAA volume transports is determined by sea surface height (SSH) gradients between the Arctic Ocean and northern Baffin Bay. The sea level upstream of Lancaster Sound is mainly determined by that along the Beaufort Sea coast, which can be explained by changes in the wind regimes (cyclonic versus anticyclonic) associated with release or accumulation of freshwater in the Beaufort Gyre. Sea level variations downstream of Lancaster Sound and Nares Strait are connected to SSH variations in the eastern Baffin Bay and in the Labrador Sea, which can be attributed to the variability of ocean-atmosphere heat fluxes. Both processes upstream and downstream of the CAA are linked with the North Atlantic Oscillation type of atmospheric variability. The local mesh refinement of ∼5 km allows us to investigate the contribution of individual narrow straits to the Parry Channel volume transport. The volume transports through these straits show a very similar variability.
42303726
Nares Strait hydrography and salinity field from a 3-year moored array
[1] Nares Strait to the west of Greenland facilitates the exchange of heat and freshwater between the Arctic and Atlantic Oceans. This study focuses on salinity, temperature, and density measurements from Nares Strait from a mooring array deployed from 2003 to 2006. Innovative moorings requiring novel analysis methods measured seawater properties near 80.5°N, at spacing sufficient to resolve the internal Rossby deformation radius. The 3-year mean geostrophic velocity has a surface-intensified southward flow of 0.20 m s−1 against the western side of the strait and a secondary core flowing southward at 0.14 m s−1 in the middle of the strait. Data show warm salty water on the Greenland side and cold fresher water on the Ellesmere Island side, especially in the top layers. There was a clear difference in hydrographic structure between times when sea ice was drifting and when it was land fast. Ice was drifting in late summer, fall, and early winter with a strong surface-intensified geostrophic flow in the middle of the strait. Ice was land fast in late winter, spring, and early summer, when there was a subsurface core of strong geostrophic flow adjacent to the western side of the strait. Salinity variations of about 2 psu in time and space reflect a variable freshwater outflow from the Arctic Ocean. One particularly strong pulse occurred at the end of July 2005. For several days, steeply sloping isohalines indicated strong geostrophic flow down the middle of the strait coinciding with an amplified ice export from the Arctic due to strong southward winds.
55347481
Acceleration of the contribution of the Greenland and Antarctic ice sheets to sea level rise
[1] Ice sheet mass balance estimates have improved substantially in recent years using a variety of techniques, over different time periods, and at various levels of spatial detail. Considerable disparity remains between these estimates due to the inherent uncertainties of each method, the lack of detailed comparison between independent estimates, and the effect of temporal modulations in ice sheet surface mass balance. Here, we present a consistent record of mass balance for the Greenland and Antarctic ice sheets over the past two decades, validated by the comparison of two independent techniques over the last 8 years: one differencing perimeter loss from net accumulation, and one using a dense time series of time-variable gravity. We find excellent agreement between the two techniques for absolute mass loss and acceleration of mass loss. In 2006, the Greenland and Antarctic ice sheets experienced a combined mass loss of 475 ± 158 Gt/yr, equivalent to 1.3 ± 0.4 mm/yr sea level rise. Notably, the acceleration in ice sheet loss over the last 18 years was 21.9 ± 1 Gt/yr2 for Greenland and 14.5 ± 2 Gt/yr2 for Antarctica, for a combined total of 36.3 ± 2 Gt/yr2. This acceleration is 3 times larger than for mountain glaciers and ice caps (12 ± 6 Gt/yr2). If this trend continues, ice sheets will be the dominant contributor to sea level rise in the 21st century.
53651017
Increased Runoff from Melt from the Greenland Ice Sheet: A Response to Global Warming
The authors attribute significantly increased Greenland summer warmth and Greenland Ice Sheet melt and runoff since 1990 to global warming. Southern Greenland coastal and Northern Hemisphere summer temperatures were uncorrelated between the 1960s and early 1990s but were significantly positively correlated thereafter. This relationship appears to have been modulated by the North Atlantic Oscillation, whose summer index was significantly (negatively) correlated with southern Greenland summer temperatures until the early 1990s but not thereafter. Significant warming in southern Greenland since 1990, as also evidenced from Swiss Camp on the west flank of the ice sheet, therefore reflects general Northern Hemisphere and global warming. Summer 2003 was the warmest since at least 1958 in coastal southern Greenland. The second warmest coastal summer 2005 had the most extensive anomalously warm conditions over the ablation zone of the ice sheet, which caused a record melt extent. The year 2006 was the third warmest in coastal southern Greenland and had the third-highest modeled runoff in the last 49 yr from the ice sheet; five of the nine highest runoff years occurred since 2001 inclusive. Significantly rising runoff since 1958 was largely compensated by increased precipitation and snow accumulation. Also, as observed since 1987 in a single composite record at Summit, summer temperatures near the top of the ice sheet have declined slightly but not significantly, suggesting the overall ice sheet is experiencing a dichotomous response to the recent general warming: possible reasons include the ice sheet’s high thermal inertia, higher atmospheric cooling, or changes in regional wind, cloud, and/or radiation patterns.
128758794
Arctic Ocean circulation, processes and water masses: A description of observations and ideas with focus on the period prior to the International Polar Year 2007–2009
Abstract The evolving knowledge of the Arctic Ocean, its hydrography and its water masses and their transformations and circulation is reviewed starting with the observations made on Fram 1893–1896 and extending to the International Polar Year (IPY) 2007–2009. The expeditions and observations after Fram to the mid 20th century as well as the more extensive and systematic studies of water masses and circulation made from ice stations and airborne expeditions from the late 1940s to the late 1970s are briefly described. The early concepts of the connections and exchanges between the Arctic Ocean and the world ocean are also discussed. In the 1980s scientific icebreakers were beginning to enter the inner parts of the Arctic Ocean and large international programmes were launched, culminating in the IPY. The changes in the Arctic Ocean, first noted in the Atlantic layer in 1990 and shortly after in the upper layers, are described. The exchanges between the Arctic Ocean and the surrounding seas through the four main openings, Fram Strait, Barents Sea, Bering Strait and the Canadian Arctic Archipelago as well the volume and freshwater balances of the Arctic Ocean are examined.
129634989
Sea ice of the northern Canadian Arctic Archipelago
[1] Existing information concerning the pack ice and relevant climate variables of the Canadian Arctic Archipelago north of Parry Channel is summarized. This knowledge is enhanced by newly available data on ice thickness derived from 123,703 drill holes completed during the 1970s. Pack ice in this area is a mix of multiyear, second-year, and first-year ice types, with the latter subordinate except in the southeast. Ice remains land fast for more than half the year, and summertime ice concentration is high (7–9 tenths). In a typical year, less than 20% of the old ice and 50% of the first-year ice melt. There are large interannual fluctuations in ice coverage and some suggestion of a decadal cycle. The average ice thickness in late winter is 3.4 m but subregional means reach 5.5 m. The pack is a mix of two populations, one consisting largely of multiyear ice imported from the zone of heavy ridging along the periphery of the Beaufort gyre and the other consisting of a mix of relatively undeformed first-year, second-year, and multiyear ice types that grow and age within the basin. The ice of the Sverdrup Basin is strongly influenced by a flux of heat (approximately 10 W m−2) that originates in the Atlantic-derived waters of the Arctic Ocean. The drift of ice through the basin is controlled in the present climate by the formation of stable ice bridges across connecting channels. The drift is episodic. Relaxation of these controls in a warmer climate may cause deterioration in ice conditions in Canadian Arctic waters.
73596940
Exchange of sea ice between the Arctic Ocean and the Canadian Arctic Archipelago
[1] First estimates of sea ice exchange between the Arctic Ocean and the Canadian Arctic Archipelago (CAA) are obtained using six years (1997–2002) of RADARSAT ice motion. Over the period, the mean annual flux of sea ice area from the Amundsen Gulf (AG), M'Clure Strait (MS), and Queen Elizabeth Islands (QEI) are −85 ± 26 × 103, −20 ± 24 × 103, and 8 ± 6 × 103 km2. Positive/negative sign indicates Arctic outflow/inflow. Overall, net sea ice area is exported from the CAA; rough estimates suggest a mean annual volume flux of ∼102 km3 into the Canada Basin. Ice types are largely seasonal near the AG flux gate, mixed seasonal and multiyear at the MS gate, and primarily multiyear at the QEI gates. Sea ice at the QEI flux gates remains land fast for most of the year. Cross-strait gradient in sea level pressure explains more than 50% of the variance in the area flux at these passages. The role of ice exchange during the anomalous decrease in multiyear ice coverage in the Sverdrup Basin during September 1998 is examined.
130089828
Recent changes in the exchange of sea ice between the Arctic Ocean and the Canadian Arctic Archipelago
[1] Sea ice is exchanged between the Arctic Ocean and Canadian Arctic Archipelago (CAA) but has not been quantified over long time periods. The corresponding mechanisms responsible for recent variability and change also remain unidentified. To address this, we estimated the sea ice area flux between the Arctic Ocean and the M'Clure Strait and Queen Elizabeth Islands (QEI) from 1997 to 2012 for the months of May to November. Over the period, there was a mean flux of −1 × 103 km2 (±21 × 103 km2) at the M'Clure Strait and mean flux of +8 × 103 km2 (±8 × 103 km2) at the QEI (positive and negative flux signs correspond to Arctic Ocean ice inflow and outflow, respectively). The M'Clure Strait had a mean flux of +5 × 103 km2 from May to September and a mean flux of −7 × 103 km2 from October to November. The QEI gates had a mean flux of +4 × 103 km2 from August to September with negligible ice exchange from May to July and October to November. More frequent high sea level pressure anomalies over the Beaufort Sea and Canadian Basin since 2007 have reduced Arctic Ocean multiyear ice (MYI) inflow into the M'Clure Strait. The presence of MYI in the CAA originating from the Arctic Ocean has been maintained by inflow at the QEI, which has increased since 2005. These recent increases in Arctic Ocean MYI inflow into the QEI can be attributed to increased open water area within the CAA that have provided more leeway for inflow to occur.
128826265
Atmospheric controls on sea ice motion in the southern Beaufort Sea
[1] The Beaufort sea ice gyre is characterized in winter months by an anticyclonic regime associated with sea level pressure (SLP) highs. Previous studies have shown instances of a reversal in this regime in summer months with the arrival of SLP lows over the Beaufort Sea, while also demonstrating a link to variations in lower stratospheric potential vorticity. In this study we examine the role of relative vorticity in describing dynamic variability on weekly timescales from the surface to the middle stratosphere. Results from this analysis show that the Beaufort Gyre is characterized predominantly by anticyclonic activity throughout the year for the time interval considered (from 1979 to 2000), with a summer reversal to cyclonic activity, whose strength and duration varies between years. These reversals coincide with reversals in SLP based on a correlation analysis. Comparison of ice and atmospheric relative vorticity fields in the Beaufort Sea region (BSR) for all weeks from 1979 to 2000 indicates that sea ice and lower tropospheric processes are anticorrelated at zero time lag. This is in contrast to relative vorticity fields at 10 mbar, which exhibit maximum correlation between stratospheric and sea ice responses when 10 mbar leads ice relative vorticity by 2–6 weeks.
129438169
Variability in Arctic sea ice drift
[1] Analysis of Arctic sea ice drift from 1979–1997 using a Lagrangian perspective shows the complexities of ice drift response to variations in atmospheric conditions. Changes in ice dynamics influence the redistribution of ice, and any transported material, from different source areas. Sources of ice exported to Fram Strait shifted in about 1986/87 from dominance of the Kara Sea and Severnaya Zemlya to the New Siberian Islands, East Siberian Sea, and Chukchi Sea. Average travel time of multiyear ice within the perennial pack of the central Arctic Basin, reached a maximum in 1987/88, and decreased by at least 1 year between 1984–1989 and 1990–1997. Consistent with the observations of other investigators, this decrease in ice travel time occurred following a major export or “surge” of old ice to Fram Strait from the Beaufort Gyre in 1988 through 1990, which decreased the fraction of thick, ridged ice within the central basin.
55019849
Sea ice drift in the Arctic since the 1950s
[1] Sea ice drift data (from Russian North Pole stations, various ice camps, and the International Arctic Buoy Program) and surface wind stress data from the NCAR/NCEP Reanalysis are analyzed to determine their long-term trends and causality. The study finds that both parameters (ice drift and wind stress) show gradual acceleration over last 50 years. Significant positive trends are present in both winter and summer data. The major cause of observed positive trends is increasing Arctic storm activity over the Transpolar Drift Stream caused by a shift of storm tracks toward higher latitudes. It is speculated, with some observational evidence, that the increased stirring of the ocean by winds could hasten the transition of the Arctic toward a weakly stratified ocean with a potential for deep convection and a new sink for atmospheric CO2.
55363998
Trends in Arctic sea ice drift and role of wind forcing: 1992–2009
[1] We examine the spatial trends in Arctic sea ice drift speed from satellite data and the role of wind forcing for the winter months of October through May. Between 1992 and 2009, the spatially averaged trend in drift speed within the Arctic Basin is 10.6% ± 0.9%/decade, and ranges between −4% and 16%/decade depending on the location. The mean trend is dominated by the second half of the period. In fact, for the five years after a clear break point in March 2004, the average trend increased to 46% ± 5%/decade. Over the 1992–2009 period, averaged trends of wind speed from four atmospheric reanalyses are only 1% to 2%/decade. Regionally, positive trends in wind speed (of up to 9%/decade) are seen over a large fraction of the Central Arctic, where the trends in drift speeds are highest. Spatial correlations between the basin-wide trends in wind and drift speeds are moderate (between 0.40 and 0.52). Our results suggest that changes in wind speed explain a fraction of the observed increase in drift speeds in the Central Arctic but not over the entire basin. In other regions thinning of the ice cover is a more likely cause of the increase in ice drift speed.
129632138
Variability in categories of Arctic sea ice in Fram Strait
An attempt to quantify the temporal variability in the volume composition of Arctic sea ice is presented. Categories of sea ice in the Transpolar Drift in Fram Strait are derived from monthly ice thickness distributions obtained by moored sonars (1990–2011). The inflection points on each side of the old ice modal peak are used to separate modal ice from ice which is thinner and thicker than ice in the modal range. The volume composition is then quantified through the relative amount of ice belonging to each of the three categories thin, modal, and thick ice in the monthly ice thickness distributions. The trend of thin ice was estimated to be negative at −8.8% per decade (relative to the long-term mean), which was compensated for by increasing trends in modal and thick ice of 7.9% and 4.7% per decade, respectively. A 7–8 year cycle is apparent in the thin and thick ice records, which may explain a loss of deformed ice since 2007. We also quantify how the categories contribute to the mean ice thickness over time. Thick (predominantly deformed) ice dominates the mean ice thickness, constituting on average 66% of the total mean. Following the loss of deformed ice since 2007, the contribution of thick ice to the mean decreased from 75% to 52% at the end of the record. Thin deformed ice did not contribute to this reduction; it was pressure ridges thicker than 5 m that were lost and hence caused the decrease in mean ice thickness.
129742367
Effects of melting and freezing in the Greenland sea
[1] Ice thickness and drift measurements complemented with modeling results are examined. In the East-Greenland ice drift stream (EGIS), the ice is thicker at 79°N than at 75°N in winter but similar in summer due to melting, advection, and seasonal changes of the wind pattern in Fram Strait. Ice fluxes at 79°N and 75°N vary coherently. Summer EGIS melting rates exceed 0.5 m/mo. In winter, oceanic currents govern melting/freezing processes. In the western EGIS, exposed to the cold East-Greenland Current, ice grows. In the eastern EGIS, influenced by warm Atlantic water, ice melts. East of EGIS, in Nordbukta (75–77°N), winter freezing occurs. A topographically controlled cyclonic gyre maintains a divergent Nordbukta ice drift, causing more leads, ocean cooling and ice formation, favoring deep convection. However, stratification in the Greenland Sea Gyre is poorly correlated with Nordbukta ice production, but shows coherent variations with the NAO index.
45948519
Sources and fate of freshwater exported in the East Greenland Current
Monitoring the sources and fate of freshwater in the East Greenland Current (EGC) is important, as this water has the potential to suppress deep convection in the Nordic and Labrador Seas if the outflow of freshwater from the Arctic Ocean increases in response to climate change. Here, hydrographic, oxygen isotope ratio and dissolved barium concentration sections across Denmark Strait collected in 1998 and 1999 are used to determine the freshwater composition of the EGC at these times. Comparison of meltwater fluxes at Denmark Strait and Fram Strait indicates a net melting of sea ice into the EGC between these two locations, with a significant proportion of sea ice drifting into the Nordic Seas or on to the East Greenland Shelf. We conclude that the phase of freshwater exiting the Arctic Ocean through Fram Strait is important in determining its possible impact on deep water formation in the Nordic and Labrador Seas.
140178212
Sea ice conditions and melt season duration variability within the Canadian Arctic Archipelago: 1979–2008
[1] Sea ice conditions and melt season duration within the Canadian Arctic Archipelago (CAA) were investigated from 1979–2008. The CAA is exhibiting statistically significant decreases in average September total sea ice area at −8.7% decade−1. The melt season duration within the CAA is increasing significantly at 7 days decade−1. 2008 represented the longest melt season duration within the CAA over the satellite record at 129 days. Average September multi-year ice (MYI) area is decreasing at −6.4% decade−1 but has yet to reach statistical significance as a result of increasing MYI dynamic import from the Arctic Ocean. Results also find that the Western Parry Channel (WPC) region of the Northwest Passage (NWP) will continue to be susceptible to MYI as the transition to a summer-time sea ice free Arctic continues. The processes responsible for the temporary clearing of the WPC region of the NWP in 2007 were also identified.
55125357
Variability and change in the Canadian cryosphere
During the International Polar Year (IPY), comprehensive observational research programs were undertaken to increase our understanding of the Canadian polar cryosphere response to a changing climate. Cryospheric components considered were snow, permafrost, sea ice, freshwater ice, glaciers and ice shelves. Enhancement of conventional observing systems and retrieval algorithms for satellite measurements facilitated development of a snapshot of current cryospheric conditions, providing a baseline against which future change can be assessed. Key findings include: 1. surface air temperatures across the Canadian Arctic exhibit a warming trend in all seasons over the past 40 years. A consistent pan-cryospheric response to these warming temperatures is evident through the analysis of multi-decadal datasets; 2. in recent years (including the IPY period) a higher rate of change was observed compared to previous decades including warming permafrost, reduction in snow cover extent and duration, reduction in summer sea ice extent, increased mass loss from glaciers, and thinning and break-up of the remaining Canadian ice shelves. These changes illustrate both a reduction in the spatial extent and mass of the cryosphere and an increase in the temporal persistence of melt related parameters. The observed changes in the cryosphere have important implications for human activity including the close ties of northerners to the land, access to northern regions for natural resource development, and the integrity of northern infrastructure.
128474251
Synthesis of primary production in the Arctic Ocean: III. Nitrate and phosphate based estimates of net community production
Abstract Combining nitrate, nitrite and phosphate data from several sources with additional quality control produced a database that eliminates many questionable values. This database, in turn, facilitated estimation of net community production (NCP) in the Arctic Marine System (AMS). In some regions, the new database enabled quantitative calculation of NCP over the vegetative season from changes in nutrient concentrations. In others, useful inferences were possible based on nutrient concentration patterns. This analysis demonstrates that it is possible to estimate NCP from seasonal changes in nutrients in many parts of the Arctic, however, the data were so sparse that most of our estimates for 14 sub-regions of the AMS are attended by uncertainties >50%. Nevertheless, the wide regional variation of NCP within the AMS (∼two orders of magnitude) may make the results useful. NCP for the entire AMS was estimated as 345 ± 72 Tg C over the vegetative season. Converting this value to annual primary production (PP) as determined by typical 14C incubations suggests an annual primary production rate for the AMS of ∼1000 Tg C. We divided the AMS and its marginal seas into the same 13 sub-regions employed in the companion studies of Matrai et al. (2012) and Hill et al. (2013) and estimated NCP for each. We also made separate estimates for the Eurasian and Amerasian portions of the Arctic Basin. Significant findings include: 1. NCP in the Arctic Basin is low, but there are regional variations in the controls and in rates. In the Amerasian Basin (particularly in the Canada sub-basin), nitrate concentrations from 0 to ∼50 m are very low (∼0 μM) even in winter. Thus, nutrient limitation suppresses NCP in this region. In the Eurasian Basin, light or grazing or both may be important limiting factors since significant surface layer nutrient concentrations persist during summer. 2. Low wintertime nitrate concentrations in the upper layers of the Amerasian Basin and Northern Beaufort Sea suggest that NCP in these sub-regions may be insensitive to changes in the ice and light regimes. 3. Although tentative because of limitations in the data, we group NCP in the 14 sub-regions as follows: a. Very high NCP (∼70–100 g C m−2) in the Bering and Southern Chukchi sub-regions. b. High NCP (∼30–40 C m−2) in the Nordic and Barents seas and the Canadian Archipelago. c. Moderate NCP (>10 to ∼15 g C m−2) in the Eurasian Basin, Southern Beaufort, Southern East Siberian Sea + Laptev, Kara Sea and Greenland Shelf sub-regions. d. Low (NCP ∼ 10 g C m−2) in Northern East Siberian Sea + Laptev and Northern Chukchi sub-regions. e. Extremely low NCP (∼1–5 g C m−2) in the Northern Beaufort and Amerasian Basin sub-regions.
128431379
New insights into the spatial variability of the surface water carbon dioxide in varying sea ice conditions in the Arctic Ocean
Abstract In the summer of 2005, continuous surface water measurements of fugacity of CO 2 ( f CO 2 sw ), salinity and temperature were performed onboard the IB Oden along the Northwest Passage from Cape Farwell (South Greenland) to the Chukchi Sea. The aim was to investigate the importance of sea ice and river runoff on the spatial variability of f CO 2 and the sea–air CO 2 fluxes in the Arctic Ocean. Additional data was obtained from measurements of total alkalinity ( A T ) by discrete surface water and water column sampling in the Canadian Arctic Archipelago (CAA), on the Mackenzie shelf, and in the Bering Strait. The linear relationship between A T and salinity was used to evaluate and calculate the relative fractions of sea ice melt water and river runoff along the cruise track. High-frequency f CO 2 sw data showed rapid changes, due to variable sea ice conditions, freshwater addition, physical upwelling and biological processes. The f CO 2 sw varied between 102 and 678 μatm. Under the sea ice in the CAA and the northern Chukchi Sea, f CO 2 sw were largely CO 2 undersaturated of approximately 100 μatm lower than the atmospheric level. This suggested CO 2 uptake by biological production and limited sea–air CO 2 gas exchange due to the ice cover. In open areas, such as the relatively fresh water of the Mackenzie shelf and the Bering Strait, the f CO 2 sw values were close to the atmospheric CO 2 level. Upwelling of saline and relatively warm water at the Cape Bathurst caused a dramatic f CO 2 sw increase of about 100 μatm relative to the values in the CAA. At the southern part of the Chukchi Peninsula we found the highest f CO 2 sw values and the water was CO 2 supersaturated, likely due to upwelling. In the study area, the calculated sea–air CO 2 flux varied between an oceanic CO 2 sink of 140 mmol m −2  d −1 and an oceanic source of 18 mmol m −2  d −1 . However, in the CAA and the northern Chukchi Sea, the sea ice cover prevented gas exchange, and the CO 2 fluxes were probably negligible at this time of the year. Assuming that the water was exposed to the atmosphere by total melting and gas exchange would be the only process, the CO 2 undersaturated water in the ice-covered areas will not have the time to reach the atmospheric CO 2 value, before the formation of new sea ice. This study highlights the value of using high-frequency measurements to gain increased insight into the variable and complex conditions, encountered on the shelves in the Arctic Ocean.
62799868
Seasonal changes in the sinking export of particulate material under first-year sea ice on the Mackenzie Shelf (western Canadian Arctic)
The sinking export of particulate material under landfast first-year sea ice was studied from the winter period to spring melt on the Mackenzie Shelf, western Canadian Arctic. Short-term particle interceptor traps were deployed at 1, 15, and 25 m under the ice on 16 consecutive occasions from 23 February to 20 June 2004. The sinking material was analyzed for chlorophyll (chl) a, phaeo- pigments, total particulate carbon (TPC), particulate organic carbon and nitrogen (POC and PON), and biogenic silica (BioSi). The sinking fluxes of chl a and BioSi increased steadily after 19 March and until the onset of spring melt (26 May), after which they increased considerably. The contribution of large algae (> 5 µm) to the total chl a sinking flux also increased after 19 March, reflecting an increas- ing contribution of diatoms to the sinking export of algal material. Accordingly, chl a sinking fluxes at 1 m showed a significant linear relationship with bottom ice chl a biomass. On average, 46% of the chl a exported at 1 m was lost in the upper 25 m. POC was the main component of the TPC sinking fluxes throughout the study. POC sinking fluxes remained fairly stable until the onset of spring melt, after which a considerable increase was observed. High POC:chl a ratios indicated a significant con- tribution of non-algal material to the sinking POC. The daily sinking loss rate of chl a, POC, and PON from the sea ice and interfacial layer (top 1 m of the water column) varied seasonally and was high- est during the winter period. Our results illustrate the continuous downward sinking export of organic material under landfast ice, from winter throughout late spring.
140748067
Vertical stability and the annual dynamics of nutrients and chlorophyll fluorescence in the coastal, southeast Beaufort Sea
[1] The first quasi-annual time series of nutrients and chlorophyll fluorescence in the southeast Beaufort Sea showed that mixing, whether driven by wind, local convection, or brine rejection, and the ensuing replenishment of nutrients at the surface were minimal during autumn and winter. Anomalously high inventories of nutrients were observed briefly in late December, coinciding with the passage of an eddy generated offshore. The concentrations of NO3− in the upper mixed layer were otherwise low and increased slowly from January to April. The coincident decline of NO2− suggested nitrification near the surface. The vernal drawdown of NO3− in 2004 began at the ice-water interface during May, leaving as little as 0.9 μM of NO3− when the ice broke up. A subsurface chlorophyll maximum (SCM) developed promptly and deepened with the nitracline until early August. The diatom-dominated SCM possibly mediated half of the seasonal NO3− consumption while generating the primary NO2− maximum. Dissolved inorganic carbon and soluble reactive phosphorus above the SCM continued to decline after NO3− was depleted, indicating that net community production (NCP) exceeded NO3− -based new production. These dynamics contrast with those of productive Arctic waters where nutrient replenishment in the upper euphotic zone is extensive and NCP is fueled primarily by allochthonous NO3−. The projected increase in the supply of heat and freshwater to the Arctic should bolster vertical stability, further reduce NO3− -based new production, and increase the relative contribution of the SCM. This trend might be reversed locally or regionally by the physical forcing events that episodically deliver nutrients to the upper euphotic zone.
129914035
The fate of production in the central Arctic Ocean - top-down regulation by zooplankton expatriates?
Abstract We estimated primary and bacterial production, mineral nutrients, suspended chlorophyll a (Chl), particulate organic carbon (POC) and nitrogen (PON), abundance of planktonic organisms, mesozooplankton fecal pellet production, and the vertical flux of organic particles of the central Arctic Ocean (Amundsen basin, 89–88° N) during a 3 week quasi-Lagrangian ice drift experiment at the peak of the productive season (August 2001). A visual estimate of ≈15% ice-free surface, plus numerous melt ponds on ice sheets, supported a planktonic particulate primary production of 50–150 mg C m −2  d −1 (mean 93 mg C m −2  d −1 , n  = 7), mostly confined to the upper 10 m of the nutrient replete water column. The surface mixed layer was separated from the rest of the water column by a strong halocline at 20 m depth. Phototrophic biomass was low, generally 0.03–0.3 mg Chl m −3 in the upper 20 m and −3 below, dominated by various flagellates, dinoflagellates and diatoms. Bacterial abundance (typically 3.7–5.3 × 10 5 , mean 4.1 × 10 5  cells ml −1 in the upper 20 m and 1.3–3.7 × 10 5 , mean 1.9 × 10 5  cells ml −1 below) and Chl concentrations were closely correlated ( r  = 0.75). Mineral nutrients (3 μmol NO 3  l −1 , 0.45 μmol PO 4  l −1 , 4–5 μmol SiO 4  l −1 ) were probably not limiting the primary production in the upper layer. Suspended POC concentration was ∼30–105 (mean 53) mg C m −3 and PON ∼5.4–14.9 (mean 8.2) mg N m −3 with no clear vertical trend. The vertical flux of POC in the upper 30–100 m water column was ∼37–92 (mean 55) mg C m −2  d −1 without clear decrease with depth, and was quite similar at the six investigated stations. The mesozooplankton biomass (≈2 g DW m −2 , mostly in the upper 50 m water column) was dominated by adult females of the large calanoid copepods Calanus hyperboreus and Calanus glacialis (≈1.6 g DW m −2 ). The grazing of these copepods (estimated via fecal pellet production rates) was ≈15 mg C m −2  d −1 , being on the order of 3% and 20% of the expected food-saturated ingestion rates of C. hyperboreus and C. glacialis , respectively. The stage structure of these copepods, dominated by adult females, and their unsatisfied grazing capacity during peak productive period suggest allochthonous origin of these species from productive shelf areas, supported by their long life span and the prevailing surface currents in the Arctic Ocean. We propose that the grazing capacity of the expatriated mesozooplankton population would match the potential seasonal increase of primary production in the future decreased ice perspective, diminishing the likelihood of algal blooms.
129556097
Development and validation of a one-dimensional snow-ice algae model against observations in Resolute Passage,
[1] Ice algae are an important component of the carbon cycle in the Arctic. We investigate the dynamics of an ice algae bloom by coupling an ice algae‐nutrient model with a multilayer s coordinate thermodynamic sea ice model. The model is tested with the simulation of an algal bloom at the base of first‐year ice over the spring. Model output is compared with data from Barrow Strait in the Canadian Arctic Archipelago. Snow cover, through its influence on ice melt, is a dominant factor controlling the decline of the bloom in the model, a finding that supports past studies. The results show that under a higher snow cover (20 cm), biomass in the early stages of the algal bloom is less than expected from the observed data. This discrepancy is due to the severely light‐limited algal growth, despite the close match between simulated and observed under‐ice photosynthetically active radiation. This result raises issues of how photosynthetic parameters as well as radiative transfer is represented in one‐dimensional ice models. This study also shows that for higher algal concentrations, when biomass is split over multiple layers rather than concentrated in one layer at the ice base, there is a reduction in algae accumulation, a result of self shading. In addition, experiments show a sensitivity of total biomass to the oceanic heat flux and ice layer thickness, both of which affect biomass loss at the ice base. Being able to accurately model physical conditions is essential before the seasonal dynamics of ice algae can be accurately modeled, and some recommendations for improvement are discussed.
53603389
Timing of blooms, algal food quality and Calanus glacialis reproduction and growth in a changing Arctic
The Arctic bloom consists of two distinct categories of primary producers, ice algae growing within and on the underside of the sea ice, and phytoplankton growing in open waters. Long chain omega-3 fatty acids, a subgroup of polyunsaturated fatty acids (PUFAs) produced exclusively by these algae, are essential to all marine organisms for successful reproduction, growth, and development. During an extensive field study in the Arctic shelf seas, we followed the seasonal biomass development of ice algae and phytoplankton and their food quality in terms of their relative PUFA content. The first PUFA-peak occurred in late April during solid ice cover at the onset of the ice algal bloom, and the second PUFA-peak occurred in early July just after the ice break-up at the onset of the phytoplankton bloom. The reproduction and growth of the key Arctic grazer Calanus glacialis perfectly coincided with these two bloom events. Females of C. glacialis utilized the high-quality ice algal bloom to fuel early maturation and reproduction, whereas the resulting offspring had access to ample high-quality food during the phytoplankton bloom 2 months later. Reduction in sea ice thickness and coverage area will alter the current primary production regime due to earlier ice break-up and onset of the phytoplankton bloom. A potential mismatch between the two primary production peaks of high-quality food and the reproductive cycle of key Arctic grazers may have negative consequences for the entire lipid-driven Arctic marine ecosystem.
15449428
What controls primary production in the Arctic Ocean? Results from an intercomparison of five general circulation models with biogeochemistry
As a part of Arctic Ocean Intercomparison Project, results from five coupled physical and biological ocean models were compared for the Arctic domain, defined here as north of 66.6°N. The global and regional (Arctic Ocean (AO)–only) models included in the intercomparison show similar features in terms of the distribution of present-day water column–integrated primary production and are broadly in agreement with in situ and satellite-derived data. However, the physical factors controlling this distribution differ between the models. The intercomparison between models finds substantial variation in the depth of winter mixing, one of the main mechanisms supplying inorganic nutrients over the majority of the AO. Although all models manifest similar level of light limitation owing to general agreement on the ice distribution, the amount of nutrients available for plankton utilization is different between models. Thus the participating models disagree on a fundamental question: which factor, light or nutrients, controls present-day Arctic productivity. These differences between models may not be detrimental in determining present-day AO primary production since both light and nutrient limitation are tightly coupled to the presence of sea ice. Essentially, as long as at least one of the two limiting factors is reproduced correctly, simulated total primary production will be close to that observed. However, if the retreat of Arctic sea ice continues into the future as expected, a decoupling between sea ice and nutrient limitation will occur, and the predictive capabilities of the models may potentially diminish unless more effort is spent on verifying the mechanisms of nutrient supply. Our study once again emphasizes the importance of a realistic representation of ocean physics, in particular vertical mixing, as a necessary foundation for ecosystem modeling and predictions.
140625264
Evaluating primary and secondary production in an Arctic Ocean void of summer sea ice: An experimental simulation approach
Abstract The gross primary (GPP) and secondary production in the Arctic Basin, Eurasian shelves and the Barents Sea were investigated through the physically–biologically coupled, 3D SINMOD model with 20 km grid size. The model was applied in an experimental setting where a control run had atmospheric forcing from the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis data. In order to test the effect of how retreating ice cover in the forthcoming century may affect the productivity through physical processes in the Arctic Ocean we added a latitude dependent air temperature starting at 1 °C at 40°N increasing to +2,+4,+6 and +8 °C at 90°N to the temperature forcing taken from ECMWF data. The model indicates that gross primary production (GPP) increases along the temperature gradient both in the Arctic Basin and along the Eurasian shelves from approximately 10 to 40 and 30 to 60 g C m −2  y −1 , respectively. In contrast, GPP in the Barents Sea was more or less constant (ca. 100 g C m −2  y −1 ). For secondary production (key mesozooplankton species Calanus finmarchicus and Calanus glacialis ) the results of the experimental runs are more complex. With an air temperature increase towards +8 °C secondary production of C. glacialis in the Barents Sea dropped from about 3.9 to 0.3 g C m −2  y −1 , while that of the Arctic Basin and Eurasian shelf increased from approximately −0.1 to 1.5 and 1.4 to 2.4 g C m −2  y −1 , respectively. Secondary production changes are unevenly distributed spatially during future warming with the most significant increases occurring along the Eurasian shelves and the Chukchi Sea. Reductions are predicted for the Kara Sea and northern Baffin Bay. During warming and among the key mesozooplankton species the distribution of C. finmarchicus is constrained to the Barents Sea and eastern Fram Strait while C. glacialis almost disappears from the northern Barents Sea, the western Fram Strait and northern Baffin Bay. In contrast, this typical Arctic species expands to the Arctic Basin and on and off the Eurasian shelf, in particular the Chukchi and East Siberian Seas.
98498637
Denitrification and anammox activity in Arctic marine sediments
We measured rates of N2 production through anaerobic NH oxidation with NO (anammox) and denitrification 12 42 in permanently cold (from 21.78 Ct o 4 8C) sediments off the east and west coasts of Greenland. The investigated sites (36- to 100-m water depth) covered sediments in which carbon contents ranged from 0.3 to 3.2 dry weight %, O2 uptake rates ranged from 3.4 to 8.3 mmol m 22 d 21 ,O 2 penetration depths ranged from 0.25 to 1.70 cm, and bottom-water NO concentrations ranged from 0.3 to 15.3 mmol L 21 . Total N2 production was 34‐344 mmol N m 22 2 3 d 21 , of which anammox accounted for 1‐92 mmol N m 22 d 21 (1‐35% of total) and denitrification for 33‐265mmol Nm 22 d 21 . At one of the high-Arctic sites, anammox activity had an optimum temperature (Topt )o f 12 8C, while that of bacterial denitrification was 248C. According to the classical temperature scheme for metabolic growth, the anammox response was psychrophilic, while denitrification was psychrotrophic. Although Topt was considerably higher than in situ temperatures, rates of denitrification and anammox were still high at 21.38C, reaching 17% and 40%, respectively, of those found at Topt. The activation energies, Ea, of anammox and denitrification were 51.0 and 60.6 kJ mol 21 , respectively, and the corresponding Q10 values were 2.2 and 2.4. Rates of anammox were linearly correlated with bottom-water NO concentrations (r 2 5 0.96, p , 0.0001, n 5 11) at the investigated sites. We 2 3 suggest that the slow-growing anammox bacteria are favored in sediments with high and stable NO conditions. 2 3
24315307
Denitrification activity and oxygen dynamics in Arctic sea ice
Denitrification and oxygen dynamics were investigated in the sea ice of Franklin Bay (70°N), Canada. These investigations were complemented with measurements of denitrification rates in sea ice from different parts of the Arctic (69°N–85°N). Potential for bacterial denitrification activity (5–194 μmol N m−2 day−1) and anammox activity (3–5 μmol N m−2 day−1) in melt water from both first-year and multi-year sea ice was found. These values correspond to 27 and 7%, respectively, of the benthic denitrification and anammox activities in Arctic sediments. Although we report only potential denitrification and anammox rates, we present several indications that active denitrification in sea ice may occur in Franklin Bay (and elsewhere): (1) despite sea ice-algal primary production in the lower sea ice layers, heterotrophic activity resulted in net oxygen consumption in the sea ice of 1–3 μmol l−1 sea ice per day at in situ light conditions, suggesting that O2 depletion may occur prior to the spring bloom. (2) The ample organic carbon (DOC) and NO3− present in sea ice may support an active denitrification population. (3) Measurements of O2 conditions in melted sea ice cores showed very low bulk concentrations, and in some cases anoxic conditions prevailed. (4) Laboratory studies using planar optodes for measuring the high-resolution two-dimensional O2 distributions in sea ice confirmed the very dynamic and heterogeneous O2 distribution in sea ice, displaying a mosaic of microsites of high and low O2 concentrations. Brine enclosures and channels were strongly O2 depleted in actively melting sea ice, and anoxic conditions in parts of the brine system would favour anaerobic processes.
32674689
The North East Water polynya (Greenland Sea)
The nutrient and phytoplankton distributions in the North East Water polynya (NEW) were determined in June 1991. At Norske Øer Ice Barrier (the polynya's southern boundary), water was upwelled, but vertical instability precluded the development of phytoplankton blooms. Along the length of the northward coastal current, part of the anticyclonic circulation in this area, the vertical stability increased to the north by the input of melt water and solar heating. This caused a gradual increase in phytoplankton biomass and a decrease in nutrient concentrations until, in the northernmost area, nitrate was depleted at the surface, and sub-surface maxima of chlorophyll a were observed. The band of high chlorophyll a concentrations extending from this area to the south along the eastern margin of the polynya was interpreted as the presence of phytoplankton advected by the local circulation. The phytoplankton communities, consisting mainly of flagellates and diatoms, were typical for the beginning of phytoplankton development in ice-covered areas. They seemed to be partially released from melting ice. Three communities were distinguished, which represented, firstly, the upwelled water and its northern extension, secondly, an area of high phytoplankton biomass in the northwestern part of the polynya, and thirdly, the pack-ice region. The major taxa co-occurred at all stations, with only their relative importance changed. The nutrient concentrations in the NEW were different from those in the adjacent areas. The low nitrate values of about 4 μM in the upper 70 m, found to be representative for the beginning of the growth season, imposed limitations on the overall phytoplankton production. Therefore, fertilization mechanisms such as upwelling along the Norske Øer Ice Barrier are important for local nutrient replenishment during the period of active phytoplankton growth. Eventually, silicate and phosphate supplied in higher concentrations by jets of the Arctic outflow may also support phytoplankton production, although these nutrients were not limiting during this study. The high-nutrient jets were detected in the upper 100 m of the water column at the eastern boundary of the polynya.
128835686
Nutrient status of the Northeast Water Polynya
The nutrient distribution in the Northeast Water Polynya (NEW) was investigated intensively between the end of May and the beginning of August 1993 during the R/V Polarstern cruise ARK IX. The major characteristics were low initial nitrate concentrations (ca. 4 μM) in the surface mixed layer of the East Greenland Shelf Water, accompanied by high silicate values (ca. 10–14 μM). These concentrations were not reduced by phytoplankton growth. Silicate was rather homogeneously distributed in the entire water column, whereas nitrate increased continuously with depth to about 13 μM. Phosphate concentrations were about 1.1 μM and had a similar distribution to that of silicate. During the course of the summer, nutrients became depleted, and nitrate was exhausted in large parts of the NEW. Silicate was reduced to values of less than 2 μM at some stations which implies that diatom growth continued despite nitrate depletion, ammonium serving as a nitrogen source. The polynya is fertilised by water with the initial nutrient concentrations downstream of the Norske Oer Ice Shelf. This process continuously supplies nutrients to the surface throughout the year and these are transported northward by the anticyclonic surface circulation following the topography of the trough system. The northern boundary of this tongue of relatively nutrient-rich water is controlled by the uptake of nutrients by phytoplankton in summer. Its extemsion is variable due to interactions between biological processes, circulation and ice cover. In the Ob Bank region the nutrient distribution can be altered by the inflow of Polar Water from the north when strong northerly winds prevail as happened during the first part of the study.
128419237
Respiration, mineralization, and biochemical properties of the particulate matter in the southern Nansen Basin water column in April 1981
Abstract Determinations of the activity of the respiratory electron transport system (ETS), during the FRAM III expedition permit us to estimate oxygen utilization rates ( R O 2 ) from the surface to 2000 m under the polar pack ice in the Nansen Basin just north of Svalbard (83°N, 7°E) during April 1981. We found R O 2 at in situ temperatures ranging from 20 pM O 2  min −1 just below the ice to 0.2 pM O 2  min −1 at 2000 m. These rates are low compared to most other ocean regions, but they could decrease particulate organic carbon and nitrogen by 76% and 74%, respectively, over a period of ∼6 months. The R O 2 calculations based on measurements made at 0 °C yielded a power function of R O 2 vs. depth ( Z ) of R O 2 =67 Z −0.5534 . When this R O 2 profile was superimposed on a more recent oxygen utilization rate profile made using the 3 He– 3 H–AOU method (OUR), in the same vicinity of the Nansen Basin during 1987 (OUR=52 Z –0.4058 , [Zheng, Y., Schlosser, P., Swift, J.W., Jones, E.P., 1997. Oxygen utilization rates in the Nansen Basin, Arctic Ocean: implications for new production. Deep Sea Research I 44, 1923–1943]), the agreement of the two profiles was close. On one hand, this was to be expected because R O 2 is the biological basis of OUR, on the other hand, it was a surprise because the methodologies are so different. Nitrate mineralization obtained from ETS activities also compared favorably with calculations based on the data of Zheng et al. [1997. Oxygen utilization rates in the Nansen Basin, Arctic Ocean: implications for new production. Deep Sea Research I 44, 1923–1943]. Chlorophyll ranged from 6 ng L −1 at 5 m to 0.06 ng L −1 at 2000 m. Particulate organic carbon (POC) decreased from 0.93 μM C just below the ice to less than 0.4 μM C at 500 m. Particulate organic nitrogen (PON) was not detectable below 70 m, however in the upper 70 m it ranged from 0.16 to 0.04 μM N. The C/N mass ratio over these depths ranged from 5.8 to 11.3. Annual carbon productivity as calculated to balance the total water column respiration was 27 g C m −2  y −1 . The integrated respiration rate between 50 and 4000 m suggests that exported production and carbon flux from the 50 m level was 24 g C m −2  y −1 . These are minimal estimates for the southern Nansen Basin because they are based on measurements made at the end of the Arctic winter.
15109454
Large, Omega-3 Rich, Pelagic Diatoms under Arctic Sea Ice: Sources and Implications for Food Webs
Pelagic primary production in Arctic seas has traditionally been viewed as biologically insignificant until after the ice breakup. There is growing evidence however, that under-ice blooms of pelagic phytoplankton may be a recurrent occurrence. During the springs of 2011 and 2012, we found substantial numbers (201–5713 cells m−3) of the large centric diatom (diameter >250 µm) Coscinodiscus centralis under the sea ice in the Canadian Arctic Archipelago near Resolute Bay, Nunavut. The highest numbers of these pelagic diatoms were observed in Barrow Strait. Spatial patterns of fatty acid profiles and stable isotopes indicated two source populations for C. centralis: a western origin with low light conditions and high nutrients, and a northern origin with lower nutrient levels and higher irradiances. Fatty acid analysis revealed that pelagic diatoms had significantly higher levels of polyunsaturated fatty acids (mean ± SD: 50.3±8.9%) compared to ice-associated producers (30.6±10.3%) in our study area. In particular, C. centralis had significantly greater proportions of the long chain omega-3 fatty acid, eicosapentaenoic acid (EPA), than ice algae (24.4±5.1% versus 13.7±5.1%, respectively). Thus, C. centralis represented a significantly higher quality food source for local herbivores than ice algae, although feeding experiments did not show clear evidence of copepod grazing on C. centralis. Our results suggest that C. centralis are able to initiate growth under pack ice in this area and provide further evidence that biological productivity in ice-covered seas may be substantially higher than previously recognized.
53701691
Polynyas and Tidal Currents in the Canadian Arctic Archipelago
A tidal model of the Canadian Arctic Archipelago was used to map the strength of the tidal currents, tidal mixing ( h / U 3), and the vertical excursion associated with the tidal currents that drive water upslope and downslope. The hot spots in these quantities correspond to the location of many of the small polynyas in the archipelago, supporting the idea that the tidal currents make an important contribution to the dynamics of many of these recurring polynyas. The potential link with tidal mixing means that these locations may have enhanced plankton production in the summer.
14207557
Bloom dynamics in early opening waters of the Arctic Ocean
We measured the isotopic composition and accumulation of particulate organic matter (POM) and the uptake of carbon (C) and nitrogen (N) in an early bloom of the most productive recurring polynya of the Arctic Ocean. The estimated compensation irradiance at the onset of the bloom was similar to the average for the North Atlantic Ocean, implying that shallow mixing was of critical importance for the bloom’s early initiation. Planktonic POM had a much lower d 13 C than ice POM, suggesting that ice-algae contributed little to the pelagic biomass. The overall isotopic fractionation of pelagic N during bloom development was consistent with in situ diatom growth under saturating irradiance and limiting NO . Soon after the ice cleared, rapid physiological changes induced an order of 2 3 magnitude increase in the C and NO uptake capacity of diatoms, leading to very high f ratios (NO uptake : total 2 2 3 3 N uptake). Most of the NO taken up appeared in the POM, so that little net release of reduced N occurred during 2 3 the period of active growth. Given the tight coupling between photosynthesis and NO uptake under N limitation, 2 3 the magnitude of primary production in the Arctic Ocean is expected to respond to changes in N supply.
129672408
Contribution of under‐ice primary production to an ice‐edge upwelling phytoplankton bloom in the Canadian Beaufort Sea
[1] The Canadian Beaufort Sea has been categorized as an oligotrophic system with the potential for enhanced production due to a nutrient-rich intermediate layer of Pacific-origin waters. Using under-ice hydrographic data collected near the ice-edge of a shallow Arctic bay, we documented an ice-edge upwelling event that brought nutrient-rich waters to the surface during June 2008. The event resulted in a 3-week long phytoplankton bloom that produced an estimated 31 g C m−2 of new production. This value was approximately twice that of previous estimates for annual production in the region, demonstrating the importance of ice-edge upwelling to the local marine ecosystem. Under-ice primary production estimates of up to 0.31 g C m−2 d−1 showed that this production was not negligible, contributing up to 22% of the daily averaged production of the ice-edge bloom. It is suggested that under-ice blooms are a widespread yet under-documented phenomenon in polar regions, which could increase in importance with the Arctic's thinning ice cover and subsequent increase in transmitted irradiance to the under-ice environment.
56097784
Turbulent nitrate fluxes in the Amundsen Gulf during ice‐covered conditions
3(2, 5) × 10 −3 m 2 s −1 and decreased exponentially to a depth of ∼50 m, below which it was roughly constant at the background value Kb =3 (2, 5) ×1 0 −6 m 2 s −1 .T he nitracline, centered around 62 m depth, was subject to an eddy diffusivity close to the background value Kb and the mean diffusive nitrate flux across the nitracline was Fnit = 0.5(0.3, 0.8) mmol m −2 d −1 . These observations are compared with other regions and the role of vertical mixing on primary production in the Amundsen Gulf is discussed. Citation: Bourgault, D., C. Hamel, F. Cyr, J.‐E. Tremblay, P. S. Galbraith, D. Dumont, and Y. Gratton (2011), Turbulent nitrate fluxes in the Amundsen Gulf during ice‐covered conditions, Geophys. Res. Lett., 38, L15602, doi:10.1029/2011GL047936.
129753703
Contribution of subsurface chlorophyll maxima to primary production in the coastal Beaufort Sea (Canadian Arctic): A model assessment
[1] Previous comprehensive investigations of the Canadian Arctic revealed that subsurface chlorophyll maxima (SCM) are widespread and long-lived structures that can contribute significantly to daily primary production in the water column. However, estimating the annual contribution of SCM to production with in situ or remote-sensing approaches is challenging in the high Arctic. For this reason and to estimate the impacts of fluctuating or changing environmental conditions on SCM, a numerical approach combining a turbulence model and an ecosystem model was implemented for the coastal Beaufort Sea. An ensemble analysis of simulations suggested that SCM contribute 65–90% of total annual primary production and that this proportion is weakly affected by ice regime, winter nitrogen (N) concentration, parameter values determining phytoplankton growth and decay or the physical forcing imposed, all varying within realistic values. Due to the persistent association between the SCM and the shallow nitracline, the pelagic ecosystem of the coastal Beaufort Sea is apparently characterized by a high ratio of new to total production, contrasting with the common assumption that oligotrophic systems are predominantly supported by recycled N and regenerated production. This study demonstrated that the use of a simple model in combination with in situ data leads to novel insights into biogeochemical processes that are otherwise very difficult to measure and track.
84373228
New estimates of microalgae production based upon nitrate reductions under sea ice in Canadian shelf seas and the Canada Basin of the Arctic Ocean
New estimates of production of sub-ice and ice microalgae in the shelf seas of the Canadian Arctic and in the Canada Basin of the Arctic Ocean derived from reduction of nitrates in the water column, as recorded in time series available in publicly held data bases, suggest that it is of greater magnitude (up to 30 g C m−2 year−1) and represent a higher proportion (up to 50 % on the shelf and 90 % in the Canada Basin) of net community production than previously estimated for both areas.
129373497
Carbon budget of sea‐ice algae in spring: Evidence of a significant transfer to zooplankton grazers
The fate of ice-bottom algae, before and after release from the first-year sea ice into the water column, was assessed during the period of ice-algal growth and decline in Resolute Passage (Canadian Arctic). During spring 1992 (from April to June), algae in the bottom ice layer and those suspended and sinking in the upper water column (top 15 m) were sampled approximately every 4 days. Ice-bottom chlorophyll a reached a maximum concentration of 160 mg m−2 in mid-May, after which it decreased to lower values. In the water column, chlorophyll a concentrations were low until the period of ice-algal decline (∼0.1 mg m−3), with most biomass in the 65% of total export) and that ice-algae were ingested by under-ice grazers after release from the ice. These results stress the importance of ice algae for pelagic consumers during the early stages of ice melt and show that the transfer of ice algae to higher trophic levels extends beyond the period of maximum algal production in the ice bottom.
140165689
Productivity of sea ice algae: in situ vs. Incubator methods
Abstract Algae of annual sea ice in the high Arctic (Resolute Passage, N.W.T.) gave little evidence of serious photosynthetic impairment during the seasonal decline of the bottom ice bloom when measured in a light-gradient incubator using a popular technique. Measurements made in situ with a novel sampling and incubating device, however, yielded much lower production rates than expected from the incubator measurements. Maximum assimilation numbers averaged 0.223 mgC·mgChl a −1 ·h −1 in incubator experiments but only 0.018 in situ, while photosynthetic efficiency averaged 0.0137 and 0.0069 [mgC·mgChl a −1 ·h −1 ]·[ μ mol photons·m −2 ·s −1 ] −1 in the incubator and in sutu, respectively. Problems of tracer diffusion, temperature differentials and extracellullar release of dissolved organic carbon can help explain the discrepancy, but differences in the spectral availability of light (PUR) between incubator and estimated in situ conditions would tend to worsen the disagreement. Bottom ice algae appear to remain viable and potentially productive during the decline of the bloom, but may achieve relatively little production in situ, depending on which technique for measuring production is considered most accurate.
128755419
Nutrient fluxes during extended blooms of Arctic ice algae
Estimates of nutrient demand by dense mats of ice algae in the high Arctic indicate that substantial nutrient fluxes are necessary to satisfy the observed growth over the 2-month bloom. In our study area, Barrow Strait, the quantity of nutrients in the surface-mixed layer is about 3–10 times greater than estimates of total demand during the bloom, and nutrient fluxes in the water column are estimated to be of the same order of magnitude as algal demand. The fluxes in the water column are predicted to vary by more than an order of magnitude over the fortnightly tidal cycle, assuming that fluxes depend upon the strength of tidal currents and the vertical nutrient gradients. In the latter half of the bloom, when biomass levels are high, it appears that established populations of ice algae may experience cyclic conditions of nutrient limitation during neap tides when nutrient fluxes are minimal. Contributions from regeneration and brine exclusion from the ice sheet appear to satisfy only a portion of the bloom's total requirement for nutrients.
140668189
Nutrients, oxygen, and inferred new production in the Northeast Water Polynya, 1992
Nutrient and oxygen distributions were measured during a hydrographic survey of the Northeast Water Polynya off the northeast coast of Greenland (77–81°N, 6–17°W) during July–August 1992 and were interpreted in the context of satellite imagery of the region. Satellite imagery revealed a convoluted plume of cold water flowing along isobaths from underneath fast ice in the southwestern portion of the polynya toward the northeast. This plume carried relatively high nutrient and low oxygen inventories. Nitrate to phosphate ratios were low in the polar water, consistent with an ultimate source of this water mass in the Pacific sector of the Arctic Ocean. It is hypothesized that the low N:P Arctic outflow might be the cause of nitrate limitation along the east coast of America as far as Cape Hatteras. Gradients of both nutrients and oxygen inventories in the euphotic zone were observed along and across the axis of mean flow within the polynya and are shown to be due to net production of organic matter. On the basis of these spatial gradients of nitrate and oxygen, an assumed along-axis current velocity of 10 cm s−1, and the observed relationships of biologically removed inorganic carbon with nitrate and oxygen, the net organic matter production was estimated to be 40–60 mmol(C) m−2 d−1. This represents the organic carbon available for export from the polynya euphotic zone. Nutrient-deficient and oxygen-rich waters were observed merging with the southward flowing East Greenland Current, suggestive of possible export, however, the ultimate fate of organic carbon produced within the polynya requires further study.
38378097
The 2007 Bering Strait oceanic heat flux and anomalous Arctic sea‐ice retreat
[1] To illuminate the role of Pacific Waters in the 2007 Arctic sea-ice retreat, we use observational data to estimate Bering Strait volume and heat transports from 1991 to 2007. In 2007, both annual mean transport and temperatures are at record-length highs. Heat fluxes increase from 2001 to a 2007 maximum, 5–6 × 1020 J/yr. This is twice the 2001 heat flux, comparable to the annual shortwave radiative flux into the Chukchi Sea, and enough to melt 1/3rd of the 2007 seasonal Arctic sea-ice loss. We suggest the Bering Strait inflow influences sea-ice by providing a trigger for the onset of solar-driven melt, a conduit for oceanic heat into the Arctic, and (due to long transit times) a subsurface heat source within the Arctic in winter. The substantial interannual variability reflects temperature and transport changes, the latter (especially recently) being significantly affected by variability (> 0.2 Sv equivalent) in the Pacific-Arctic pressure-head driving the flow.
24739701
Phytoplankton in the Marginal Ice Zone of the Greenland Sea during summer, 1984
SummaryPhytoplankton biomass and species composition were studied in transects through the ice edge region of the Greeland Sea from 19 July to 8 August 1984. Biomass was estimated by vertical in situ chlorophyll fluorescence and pigment extraction of discrete samples. Preserved material was used for identification of phytoplankton species and calculation of their relative abundances. The results suggest that the various geographical regions of the Greenland Sea differ considerably in their phytoplankton development. Autotrophic biomass and species composition were closely associated with the extent of the annual and seasonal ice cover, hydrographic conditions, nutrient availability and the water masses typical of the different domains. In the NE Greenland polynya a deep mixed layer inhibited the development of a phytoplankton bloom, whereas greatest biomass concentrations were associated with a receding ice edge on the E Greenland Shelf. In the Fram Strait, the position of the relatively stationary ice edge is controlled by frontal dynamics, currents and wind. Due to rapidly changing physical and chemical conditions, phytoplankton biomass showed great variability between stations. High chlorophyll a concentrations may develop locally where melting ice causes stratification or can result from passive accumulation in eddies. In July/August 84 the Fram Strait area was dominated by a typical summer population of flagellates and large diatom species.
25664684
Relationships of food uptake and body components of Calanus finmarchicus, C. glacialis and C. hyperboreus to particulate matter and water characteristics in Fram Strait
SummaryDuring MIZEX'83 and MIZEX'84 food composition and food uptake by three Calanus species were investigated in the northern Greenland Sea. Samples were obtained from open water, the marginal ice zone, the pack ice region and the East Greenland shelf polynya. Food uptake of Calanus spp. was determined in ship-board incubation experiments under in situ conditions and volume of particulate matter in the upper 300 m of the water column was measured. Principal components analysis was used for data evaluation. Under the pack ice strongly reduced amounts of particulate matter in the euphotic zone were found while concentrations were elevated in the marginal ice zone and the East Greenland shelf polynya. Food uptake of C. finmarchicus was correlated to food concentration. In the pack ice region ingestion was close to zero for all species investigated. Likewise body weights were significantly lower than in MIZ or polynya. Principal components analysis of physical data shows a clustering of MIZ station groups at high temperature and salinity, clearly separated from pack ice and polynya stations. Analysis of biological data results in the same grouping of stations demonstrating a strong influence of hydrographic conditions on plankton development. It is concluded that herbivorous copepods cannot sustain themselves in the pack ice region but only at places of high productivity like marginal ice zone and East Greenland shelf polynya.
55779012
Near-ubiquity of ice-edge blooms in the Arctic
Abstract. Ice-edge blooms are significant features of Arctic primary production, yet have received relatively little attention. Here we combine satellite ocean colour and sea-ice data in a pan-Arctic study. Ice-edge blooms occur in all seasonally ice-covered areas and from spring to late summer, being observed in 77–89% of locations for which adequate data exist, and usually peaking within 20 days of ice retreat. They sometimes form long belts along the ice-edge (greater than 100 km), although smaller structures were also found. The bloom peak is on average more than 1 mg m−3, with major blooms more than 10 mg m−3, and is usually located close to the ice-edge, though not always. Some propagate behind the receding ice-edge over hundreds of kilometres and over several months, while others remain stationary. The strong connection between ice retreat and productivity suggests that the ongoing changes in Arctic sea-ice may have a significant impact on higher trophic levels and local fish stocks.
130014954
Primary productivity and new production in the Northeast Water (Greenland) Polynya during summer 1992
The primary productivity and rates of new production were assessed in the Northeast Water Polynya during July–August 1992 by using 14C and 15N tracer techniques. The average rate of primary production for the entire region, including an approximate correction for the effects of ice cover, was 0.21 g C m−2 d−1, with the maximum observed rate being slightly over 1.1 g C m−2 d−1. Rates of new production (uncorrected for effects of ice cover) averaged 3.08 mmol N m−2 d−1. Surface f ratios (the ratio between nitrate uptake and the total inorganic nitrate uptake) averaged 0.63, and depth-integrated f ratios equaled 0.69. It appeared that the water column in general was bilayered, in that f ratios were reduced near the surface in low (less than 2 μM) nitrate waters and increased deeper in the euphotic zone. Ammonium concentrations and uptake were consistently low throughout the region. Growth rates were modest, with surface growth rates averaging 0.33 per day. A simple relationship among the attenuation of solar radiation by sea ice (and its associated snow cover and microbial community), the percentage of open water, ice thickness, water column attenuation, and phytoplankton photosynthesis is described. The relationship is nonlinear, but, in general, nutrient-replete water column photosynthesis are largely a function of the percentage of open water rather than ice thickness. Both irradiance and nutrient fields exert strong influences on phytoplankton productivity and ultimately result in a mosaic of biomass within the polynya.
140146366
Nutrients and organic nitrogenous compounds in the marginal ice zone of the Fram Strait
Abstract During the summer of 1988 the distribution of nutrients and organic nitrogenous substances were studied in the Fram Strait area as part of the Greenland Sea project. The marginal ice zone with the Polar and Arctic Front was clearly determined by the hydrography and nutrient distribution. In the surface layer of the Arctic and Atlantic Water, nitrate was depleted. In the nutricline which was at about 30 to 50 m and below, ammonium maxima occurred. In the surface layer of the ice-covered Polar Water, nitrate was still available with about 4 μM/l. Particulate organic nitrogen was restricted to the nitrate depleted upper-water layer with values of about 3 μM/l. Concentrations of dissolved organic nitrogen (DON) were enriched in the surface layer with more than 5 μM/l but were not significantly different in the water masses. In contrast, the free amino acids followed much closer the frontal situation but contributed only less than 3% to the DON. The proportion of total dissolved amino acids was much higher with about 20% of DON. In the deeper layers below 500 m the concentrations and compositions were more uniform. High nitrate values and only about half of the DON compared to the surface layer were found. Total amino acids were low or around the detection limit. The results show that DON plays an important role in budget calculations and that a considerable part belongs to a DON fraction which may maintain a certain phytoplankton stock during nitrate depletion.
84667285
Reproduction of the Arctic copepod Calanus glacialis in Fram Strait
Egg production rates of Calanus glacialis (Jaschnov) were measured in the laboratory (in 1985) and in the field (in 1983–1984). In the laboratory, daily egg production was studied over one month at alternating feeding and fasting conditions. Spawning ceased after 3 d of starvation and started as soon as females were reintroduced to food. Egg production increased stepwise at 3-d intervals. Females survived more than nine months in captivity. In the field, egg production was measured during PREMIZEX 1983 and MIZEX 1984 at 5 and 16 stations, respectively. High egg production was found in polynyas on the East Greenland Shelf, where melt water induced stratification which supported a spring bloom. Highest egg production was converted into 6.1% body carbon female-1 d-1. Under thick pack-ice no eggs were spawned. Spawning was induced in females from a station with low food abundance by feeding them on board ship. These results from both experiments and field studies show that egg production in C. glacialis is closely related to food availability. Thus, C. glacialis exhibits a reproductive behavior similar to that of C. finmarchicus, but not C. hyperboreus, the other two dominant species in this region.
84720741
Egg production of the Arctic copepod Calanus glacialis: laboratory experiments
Egg production of single female Calanus glacialis Jaschnov fed with Thalassiosira antarctica at super-abundant concentrations (>300 μg C l-1) was determined over several weeks. Experiments were performed directly after collection from the East Greeland Current in June 1987 and 1988, and during resumed feeding after long-term starvation over 4 (October 1988), 4.5 (October 1987) and 6.5 (January 1988) mo. In addition, in June 1987, short-term starvation experiments of 5 and 15 d were conducted. Egg production was closely related to feeding in all experiments. While directly after collection eggs were produced within a few days, it took 2 wk (October 1987 and 1988) and 10 d (January 1988), respectively, to resume egg production after long-term starvation. During long-term starvation periods eggs were not laid. The decrease in total egg production with duration of starvation was due to decreasing clutch size and increasing spawning interval. In contrast, short-term starvation experiments only affected spawning interval. Interannual variability in egg production was high, with much higher clutch sizes in 1988. Average production rates in June 1988 correponded to 5% body C female-1 d-1, the maximum was 7.4% (1 274 eggs in 23 d). Carbon content of eggs was 0.40 μg egg-1. C. glacialis is well adapted to pulsed food events in the Arctic by its longevity; its ability to preserve its reproductive potential over several months; its rapid mobilization of ovaries; and by its high egg production rates. The implication of prolonged spawning capacity on life cycle studies is discussed.
129046891
Copepods in Fram Strait in summer: Distribution, feeding and metabolism
A summer study of zooplankton in the Fram Strait area of the Greenland Sea showed elevated abundances of herbivorous copepods in the marginal ice zone or ice-edge compared with copepod communities under the pack ice cover. Several physical factors contributed to this, including the large-scale current systems which deliver both North Atlantic and Arctic plankton to the ice-edge and the effect of melting ice and eddies in increasing primary productivity and standing stocks of phytoplankton. The potential importance of the ice-edge in secondary production was observed directly as increased numbers of juvenile copepods. Indirectly, it can be inferred from observations that copepods under ice-cover were ingesting only enough to meet daily metabolic demands, were metabolizing protein, and were not storing lipid. Copepods were not undertaking diel vertical migration. Abundances of female copepods at the ice-edge were largely a function of currents, while growth of juveniles was dependent on food supply which even at the ice-edge fell short of the calculated requirements of the dominant copepods.
128420028
Circulation and water masses of the East Greenland shelf
The water masses and circulation over the northern Greenland continental shelf are described based on two cruises to the region during the summers of 1979 and 1984. The cold Polar Water over the shelf was found to increase notably in salinity toward the shelf break and the East Greenland Polar Front. A colder, more saline, and relatively isolated fraction of the Polar Water was identified just above the Atlantic Intermediate Water of the front. A middepth layer, stable in time, indicates little vertical heat exchange. Warm Atlantic Intermediate Water was found to intrude close to the coast via a newly defined system of troughs in the shelf. The Polar Water was found to circulate over the shelf in a clockwise gyre. Baroclinic transports, northward near the coast with 0.58-Sv mean flow and southward elsewhere with 1.47-Sv mean flow, yielded a net southward transport in the East Greenland Current of 0.89 Sv.
129712595
Distribution, reproduction and development of Calanus species in the Northeast water in relation to environmental conditions
Abstract The vertical and horizontal distribution of mesozooplankton biomass and its composition, together with the reproduction and development of the three dominant herbivorous copepods Calanus finmarchicus, C. glacialis and C. hyperboreus , were studied in the Northeast Water between the end of May and end of July, 1993. Biomass varied between 0.15 and 10.6 g m −2 and was lower on the shallow banks. Highest biomass was found on the shelf slope and in the entrances to Belgica and Westwind Troughs. There was no seasonal trend during the study period. Among the zooplankton taxa, copepods were dominant, with 84% biomass of all other taxa, followed by chaetognaths with 14%. The large Calanus species made up 91% of copepod biomass. The most abundant species, C. glacialis , inhabited areas of low current speeds on Belgica and Ob Bank, C. hyperboreus dominated shelf slope and trough stations, while C. finmarchicus was most abundant in the Return Atlantic Current along the shelf slope and also eastern Belgica Trough. C. glacialis was the only Calanus species spawning during this period, but young copepodites of the other species were also abundant. Egg production of C. glacialis was at a maximum by our arrival and continued to at least mid August. According to the results from starvation experiments, its egg production was fuelled by food uptake, but was decoupled from phytoplankton chlorophyll until July, indicating ice-algae and microzooplankton as an alternative food source. Only when the polynya approached its maximum extent was a close relationship to phytoplankton established. Due to both spatial and temporal heterogeneity of the occurrence of young copepodite stages it was impossible to follow the growth of cohorts of developmental stages. Herbivorous carbon requirements estimated from egg production rates were mostly less than one third of the phytoplankton stock. From egg production and the distribution of young stages, the outer Westwing Trough seems to be the centre of biological activities. This may be related to the formation of young ice in winter in this area, which was found to carry a large mass of under-ice algae. High biomass but low production in Belgica Trough indicate this as an advective and expatriated community of C. finmarchicus and C. hyperboreus , where grazing is negligible, at least during early summer.
129669038
The Northeast Water Polynya during summer 1992: Distribution and aspects of secondary production of copepods
Zooplankton ecology in the Northeast Water Polynya was investigated from July 15 to August 15, 1992. The initial hypotheses were that the polynya would be a site of enhanced secondary production and that the copepod community would be composed of varying proportions of North Atlantic and Arctic species advected onto the Greenland shelf through the Northern and Southern Troughs. Striking contrasts were observed between the northern and southern regions of the shelf. The southern region was dominated numerically by the North Atlantic species Calanus finmarchicus, while species of Arctic origin (C. glacialis, C. hyperboreus, Metridia longa) dominated in the northern region. The polynya itself contained few of the herbivorous Calanus species but, instead, was dominated by the omnivore M. longa. Secondary production of C. glacialis, represented by egg production rates, was high in all regions (55–88 eggs/female/day). However, because of low abundances of the large bodied Calanus species within the polynya, it is estimated that the herbivorous copepods were not significant consumers of primary production in the polynya. Fundamentally different pathways for the cycling of carbon may exist in the northern and southern regions. Copepod communities may utilize much of the primary production in the south but only a small proportion of the primary production in the polynya, where significant proportions may be unconsumed.
129032202
Distribution of zooplankton in the Northeast Water Polynya during summer 1992
Abstract The distribution and abundances of zooplankton in the Northeast Water (NEW) Polynya during the summer of 1992 have been determined from samples collected with Bongo (this study) and MOCNESS (earlier analysis) plankton net tows. The initial hypothesis was that the troughts of the Greenland Shelf in the region of the NEW polynya would be conduits for the infusion of zooplankton species of Arctic and North Atlantic origin on to the shelf. Analysis of MOCNESS tows indicated instead that advection of zooplankton onto the shelf in the polynya region was limited, resulting in low abundances of the large herbivores in the polynya. The distribution of zooplankton determined from the 43 Bongo tows reported here strengthen this finding. Low abundances of the large herbivorous copepods and of other primarily herbivorous zooplankton taxa were observed throughout the ice-free region, in contrast to higher abundances observed further to the east in Westwind Trough or in the south in Belgica Trough. Cluster analysis was used to identify groups of co-occurring zooplankton taxa and groups of stations with similar relative compositions of zooplankton taxa. The community composition of the Belgica Trough was distinctly different from that observed in northern regions, with high abundances of open ocean copepods ( Calanus finmarchicus and C. hyperboreus ). Two types of communities were identified in the northern regions: one typical of the eastern basin (Westwind Trough) and one typical of the western basin (Norske Trough) of the northern trough. The relationship between the different zooplankton communities and the water mass characteristics was not conclusive; however, it did appear that zooplankton populations had been advected in the upper water column into the Westwind Trough from north of the study area. The low abundances of herbivorous taxa in the ice free region supported previous estimates that meso-macro zooplankton may not be significant consumers of primary production in the polynya.
128473663
Distribution and exchange of water masses in the Northeast Water polynya (Greenland Sea)
On the basis of classical hydrographic and nutrient analysis, water masses and their spreading in the Northeast Water (NEW) Polynya were investigated from RV Polarstern ARK IX (1993) data. It is shown that a local water body, East Greenland Shelf Water, occupies the top layer in the NEW and that this water is different from Polar Water exported from the Arctic Polar Ocean. Polar Water, as well as the underlying and also imported Knee Water, follows a path crossing the broad East Greenland Shelf diagonally from northeast to southwest but both waters do not enter the NEW Polynya. Intermediate waters in the NEW are also modified locally. A local source of silicate, contributing to an intermediate silicate maximum in the trough system, is identified in the centre of the anticyclonic movement over Belgica Bank. Furthermore, it is confirmed that there is no one-directional through-flow of deeper waters in the trough system. Belgica Trough and Westwind Trough contain two different water types of Atlantic origin, which are not directly related to Return Atlantic Waters. The deeper waters in Norske Trough are supplied from Belgica Trough over a sill of about 250 m depth.
129616562
Summary of the Northeast Water Polynya formation and development (Greenland sea)
Abstract The mechanisms forming the Northeast Water Polynya (NEWP), located on the shelf northeast of Greenland, are elaborated for different sub-domains of the polynya for the years 1990–1993. Sea-ice formation, sea-ice melt and the horizontal divergence of ice-floe velocity owing to winds and currents are investigated for the sub-domains. Several shelf-ice barriers of different size extend perpendicular to prevailing currents and winds causing a divergence of the ice-field flow in their lee. In summer, winds are weak and the northwand flowing coastal current in combination with Norske Oer Shelf Ice (NOSI) constitutes the dominant forcing of the Northeast Water summer polynya forming in the southern part of the NEW area. During this season the polynya gradually increases its size towards the north since the air-sea heat budget is positive then and now ice-formation takes place. In winter, strong northerly wind outbreaks push newly formed sea-ice out of Ob Bank region in the northern NEW area which is sheltered by Ob Bank Shelf Ice (OBSI) and the eastern coast of Kronprins Christians Land. Since during the winter season the air-sea temperature difference can amount to up to 30°C new ice forms rapidly balancing the ice export.
84806215
Exploratory data analysis of the interactions among physics, food web structure, and function in two Arctic polynyas
Polynyas are areas of open water in ice-covered seas, characterized by high biological productivity. The NEW (Northeast Water) and NOW (North Water) polynyas, located off the east and west coasts of Greenland, were extensively sampled in 1993 and 1998, respectively. We used principal component analysis to explore the seasonal covariations among physical, chemical, and ecological characteristics in these polynyas. In both polynyas, the most explanatory eigenvector revealed the expected seasonal development of the bloom (nutrient consumption and biomass increases) associated with declining ice cover, warming, and mixed-layer shallowing. This seasonal pattern, however, was much weaker in NEW than in NOW. No connections between the structure of the food web and recycling processes were apparent in either polynya. The analysis points to much stronger and richer interactions between the mesoplankton (i.e., diatoms–zooplankton) and microbial food webs in NOW than in NEW. The differences between the polynyas may ...
129937044
Autotrophic flagellates and diatoms in the Northeast Water polynya, Greenland: summer 1993
Copyright (c) 1996 Elsevier Science B.V. All rights reserved. Abundance, biomass and distribution of autotrophic flagellates, autotrophic dinoflagellates and diatoms were measured in the Northeast Water (NEWr Polynya during summer, 1993, using epifluorescence microscopy (EFMr and high-pressure liquid chromotography (HPLCr. Numerous discrepancies existed between results from EFM and HPLC. Phytoplankton communities determined microscopically at the depth of the chlorophyll maximum consisted primarily of flagellates in various size classes (average 1.3×10 7 cells l −1 , 8.5 μg C l −1 r and the small diatom Chaetoceros socialis (average 5×10 6 cells l −1 , 52 μg C l −1 r, with subsurface maxima of both groups usually occurring close to the nitricline. A wide variety was observed in the composition of the phytoplankton community with respect to biomass of individual taxa. The biomass of autotrophic flagellates represented on average 23% of the total autotrophic biomass in all regions of the study area as defined by water mass type. Based on carbon units derived from pigment concentrations (HPLCr, prasinophytes and haptophytes each contributed 24% to total flagellate (non-dinoflagellater biomass and chrysophytes contributed 52%. In the northeast quadrant, influenced by the East Greenland Current, haptophyte contribution dropped to 9%. Most of the biomass of autotrophic flagellates was in cells <8 μm in diameter; of diatoms, in cells <10 μm in diameter. Highest picoplankton biomass (cells <2 μmr occurred in ice-free water at moderate stability. The average contribution of autotrophic dinoflagellates to total autotrophic biomass was 6% (3 μg C l −1 , 1.7×10 5 cells l −1 r. Ratios of microscopically measured autotrophic carbon to fluorometric chlorophyll a (i.e. community C:chl ar ranged from 11−265 (avg. 61r, with maximum ratios attributable to regions dominated by C. socialis. Although differences between four areas of the NEW with respect to physical characteristics of the water column were observed, few corresponding biological differences could be verified. Similarly, phytoplankton community composition was weakly if at all correlated with physical or chemical characteristics of the water column. Future investigations should examine food web dynamics (i.e. grazingr and small-scale circulation to account for the mosaic pattern of phytoplankton features.
25838054
The Northeast Water polynya, Greenland Sea
During a pilot study in June 1991 meso-and macrozooplankton investigations were carried out in the region of the Northeast Water (NEW), a polynya located off Northeast Greenland at about 80°N. The mesozooplankton collected by bongo net was dominated by the large herbivorous copepods Calanus glacialis, C. hyperboreus and C. finmarchicus. At most stations the Calanus populations consisted of overwintering stages, except for an ice-free site in the northwestern corner of the study area, where young copepodids of C. hyperboreus and C. glacialis occurred. Young C. finmarchicus were only found at stations influenced by Atlantic water masses, whereas C. glacialis was the prevailing species on the East Greenland shelf. Egg production of this species was variable, but spawning activity appeared to be related to ambient chlorophyll a concentrations. Carbon requirements of herbivorous Zooplankton were estimated from egg production rates of C. glacialis. Due to low mesoplankton biomass, a mean of only 10% (ranging from <1% to 53%) of the phytoplankton carbon were grazed. Macrozooplankton was collected at three stations by a Rectangular Midwater Trawl (RMT 1+8). Major components were chaetognaths, hyperiid amphipods and large copepods. Macroplankton biomass was extremely low (1–3 mg AFDW m−3), about one order of magnitude less than that of the mesoplankton. Based on these limited data we hypothesize that macroplankton plays only a minor role as food for higher trophic levels and as predators controlling mesoplankton in the NEW polynya. These findings seem todisprove the concept of a rich pelagic community in the polynya amongst “a desert of ice”. They do, however, fit well with the notion of strong pelago-benthic coupling of primary production supporting a rich benthos within the polynya area.
84060596
Pathways of carbon cycling in the euphotic zone: the fate of largesized phytoplankton in the Northeast Water Polynya
The fate of large-sized phytoplankton and pathways of carbon cycling in surface waters, i.e. recycling within or export out of the euphotic zone, were investigated in the Northeast Water (NEW) Polynya (77-81 °N) from 23 May to 17 August 1993. Sampling represented a wide range of ice, hydrographic and nutrient conditions. Phytoplankton and zooplankton abundances, and phytoplankton production rates were determined in the field, whereas potential rates of grazing by copepods, dinoflagellates and appendicularians were calculated from abundances and temperature, using assumptions from the literature. The potential downward and lateral export of phytoplankton was also calculated by resolving a carbon budget for the euphotic zone. The present study suggests that, in the NEW, different pathways for the cycling of carbon existed in seasonally ice-free (in the polynya) and continuously ice-covered areas (outside the polynya). Outside the polynya, the fate of large-sized phytoplankton could not be assessed because the heterotrophic community presumably grazed on a variety of food items, including ice algae, microzooplankton and large-sized phytoplankton. In the polynya, the fate of large-sized phytoplankton production was to be mostly recycled at the beginning of sampling and to be mostly exported downward or laterally as the bloom of large-sized phytoplankton developed. Generally, copepods mostly contributed to recycling, but sometimes dinoflagellates or appendicularians alone recycled most of the large-sized phytoplankton production.
129647979
Flux of particulate matter through copepods in the Northeast water polynya
Particulate organic carbon (POC) and nitrogen (PON) production by large calanoid copepods was investigated on the northeast Greenland shelf during August 1992 and May to August 1993. Both Calanus hyperboreus and C. glacialis females, when suspended in seawater collected from the chlorophyll maximum, produced about 40 pellets per day, which contained a carbon and nitrogen content equivalent to 8% and 6% of body carbon, respectively, and 2% of body nitrogen. In experiments, the carbon:nitrogen (C:N) ratio by weight of suspended particulates, C. hyperboreus, and fecal pellets was 6.7, 7.7 and 28.5, respectively. The unusually high C:N ratio for pellets, in part, may be attributed to elevated ratios of > 20μm size fractions of particulate organic matter, the size fraction more common in the diet of these large copepods and the fraction dominated by diatoms according to microscopic and pigment data. The implied elevated C:N ratios of large phytoplankton cells were probably due to nitrogen deficiency, as shown by other studies in this region. In addition, female C. hyperboreus appeared to be more efficient in assimilating nitrogen than carbon, which also would have contributed to high C:N ratios in egested pellets. Unfractionated POC concentrations explained 54% of the variability in carbon egestion and 70% of the variability in nitrogen egestion in copepods, whereas copepod body content accounted for little of the variation on the short time scales of the experiments. Carbon egestion by C. hyperboreus was positively correlated with POC concentrations at the depth of the chlorophyll maximum, while nitrogen egestion was negatively correlated with PON concentrations in the euphotic zone. Estimates of potential community egestion rates for the upper water column indicate that copepods represent a major pathway of organic carbon transformation in this Arctic shelf system. On average, copepods may have ingested 45% of the primary production and egested fecal matter equivalent to 20% of the carbon and 12% of the nitrogen particulate flux sedimenting from the surface layer. However, several lines of evidence suggest that pellets were remineralized in the water column and, hence, may have contributed little organic carbon and nitrogen to the benthos.
129701936
Wind triggered events of phytoplankton downward flux in the Northeast Water Polynya
Phytoplankton carbon fluxes were studied in the Northeast Water (NEW) Polynya, off the eastern coast of Greenland (79� to 81� N, 6� to 17� W), during summer 1993. The downward flux of organic particles was determined during 54 days using a sediment trap moored at a fixed location, below the pycnocline (130 m). The hypothesis of the present study is that wind events were ultimately responsible for the events of diatoms downward flux recorded in the trap. Wind conditions can influence the vertical transport of phytoplankton by affecting (1) the environmental conditions (e.g. hydrostatic pressure, nutrient concentrations, and irradiance) encountered by phytoplankton during their vertical excursion, and (2) the aggregation and disaggregation of phytoplankton flocs. The first mechanism affects the physiological regulation of buoyancy, whereas the second one affects the size and shape of settling particles. Using field data (wind velocity, density profiles and phytoplankton abundance), we assessed the potential aggregation and the vertical excursion of phytoplankton in surface waters. The results show that, upstream from the trap, wind and hydrodynamic conditions were sometimes favourable to the downward export of phytoplankton. Lag-correlation between time series of wind and phytoplankton downward flux shows that flux events lagged wind events by ca. 16 days. Given that the average current velocity in the top 100 m was ca. 10 cm s � 1 , a lag of 16 days corresponded to a lateral transport of ca. 130 km, upstream from the sediment trap, where phytoplankton production was lower than at the location of the trap. According to that scenario, 21% to 60% of primary production was exported to depth during wind events. If we had assumed instead a tight spatial coupling between the material collected in the trap and the relatively high phytoplankton production at the location of the trap, we would have concluded that <7% of primary production was exported to depth. The difference between the two scenarios has great implications for the fate of phytoplankton. Our results stress the importance of investigating the spatial coupling between surface and trap data before assessing the pathways of phytoplankton carbon cycling. D 2002 Elsevier Science B.V. All rights reserved.
129848999
Sediment community biomass and respiration in the Northeast water polynya, Greenland: a numerical simulation of benthic lander and spade core data
Sediment community metabolism (oxygen demand) was measured in the Northeast Water (NEW) polynya off Greenland employing two methods: in situ benthic chambers deployed with a benthic (GOMEX) lander and shipboard laboratory Batch Micro-Incubation Chambers (BMICs) utilizing ‘cores’ recovered from USNEL box cores. The mean benthic respiration rate measured with the lander was 0.057 mM O2 m−2 h−1 (n = 5); whereas the mean measured with the BMICs was 0.11 mM O2 m−2 h−1 (n = 21; p < 0.01 that the means were the same). In terms of carbon fluxes (14 and 27 mg C m−2 d−1), these respiration rates represent ca. 5–15% of the average net primary production measured in the euphotic zone in 1992. The biomass of the bacteria, meiofauna and macrofauna were measured at each location to quantify the relationship between total community respiration and total community biomass (mean 1.42 g C m−2). Average carbon residence time in the biota, calculated by dividing the biomass by the respiration, was on the order of 50–100 days, which is comparable to relatively oligotrophic continental margins at temperate latitudes. 
 
The biomass and respiration data for the aerobic heterotrophic bacteria, the infaunal invertebrates (meiofauna and macrofauna), and the epifaunal megabenthos (two species of brittle stars) are summarized in a ‘steady-state’ solution of a sediment food chain model, in terms of carbon. This carbon budget illustrates the relative importance of the sediment-dwelling invertebrates in the benthic subsystem, compared to the bacteria and the epibenthos, during the summer open-water period in mud-lined troughs at depths of about 300 m. The input needed to drive heterotrophic respiratory processes was within the range of the input of organic matter recorded in moored, time-sequencing sediment traps. 
 
A time-dependent numerical simulation of the model was run to investigate the potential responses of the three size groups of benthos to abrupt seasonal pulses of particulate organic matter. The model suggests that there is a time lag in the increase in bottom community biomass and respiration following the POC pulse, and provides hypothetical estimates for the potential carbon storage in the summer (open water), followed by catabolic losses during each ensuing winter (ice covered). 
 
This sequence of storage and respiration may contribute to the process of seasonal CO2 ‘rectification’ (sensu Yager et al., 1995) in some Arctic ecosystems.
128638899
Benthic community patterns reflect water column processes in the Northeast Water polynya (Greenland)
Abstract Benthic community patterns were investigated in the Northeast Water polynya (Greenland) during the summers of 1992 and 1993 to elucidate to what extent the bottom fauna is influenced by the dynamics of the overlying water. Five different fractions of the benthos (foraminiferans, nematodes, polychaetes, peracarid crustaceans, and epibenthic megafauna), ranging in average adult body size over 6 orders of magnitude (from about 100 μm to about 10 cm), were sampled quantitatively at 69 stations in water depths from 40 to 515 m. Total abundances of nematodes, polychaetes and peracarid crustaceans were found to be primarily correlated with parameters characterizing the potential benthic food supply (water column pigment and nitrate concentrations, sediment bound pigments and sediment biological activity), whereas abundances of foraminiferans and megabenthos were largely associated with seabed properties. Four benthic zones were distinguished by separately analyzing the faunistic composition and distribution of the five community fractions for Ob Bank, Western Westwind Trough, Eastern Westwind Trough, and Belgica Trough. This pattern was shown principally to reflect pelagic regimes differing in surface water hydrography, ice cover and euphotic productivity. This is the first time that a synoptic study of several benthic community portions spanning such a range in sizes and life styles has been performed in a polar shelf ecosystem. Our results indicate that abundances as well as composition of Arctic benthos are largely influenced by mesoscale pelagic processes, and thus provide further evidence for the importance of the benthic-pelagic coupling in high latitude seas.
55959160
Peracarid fauna (Crustacea, Malacostraca) of the Northeast Water Polynya off Greenland: documenting close benthic-pelagic coupling in the Westwind Trough
Composition, abundance, and diversity of peracarids (Crustacea) were investigated over a period of 3 mo in the Northeast Water Polynya (NEW), off Greenland. Samples were collected from May to July 1993 during expeditions ARK IX/2 and 3 using an epibenthic sledge on RV 'Polarstern' Within the macrobenthic community peracarids were an important component of the shelf fauna and occurred in high abundance in this area together with polychaetes, molluscs and brittle stars. A total of 38322 specimens were sampled from 22 stations. Cumacea attained the highest total abundance and Amphipoda the highest d~versity. Isopoda were of medium abundance, Mysidacea less abundant, and Tanaidacea least abundant. In total 229 species were found. Differences in composition, abundance and diversity do not reflect bathymetric gradients, but mainly the availability of food (phytoplankton and especially ice algae) and, hence, the temporal and spatial opening of the polynya. Thus primary production and hydrographic condit~ons (lateral advection due to the ant~cyclonic gyre around Belgica Bank) are the main biological and physical parameters influencing the peracarid crustacean community, documenting a close coupling between primary production and the benthic community in the eastern Westwind Trough. The high abundance of Peracarida, which are also capable of burrowing in the upper sediment layers, indicates their importance for benthic carbon cycling.
24205726
Abundance, diversity and community patterns of epibenthic- and benthic-boundary layer peracarid crustaceans at 75°N off East Greenland
Abstract During an expedition of RV Polarstern in 1994, a vertical transect (about 200-, 300-, 450-, 800-, 1,500- and 2,200-m depth) and a horizontal transect (of three stations at about 800-m depth) were sampled at 75°N off Greenland with an epibenthic sledge in order to obtain information on the abundance, diversity and community patterns of epi- and suprabenthic peracarid crustaceans, which are known to be an important component of the macrofauna along the Greenland continental shelf and slope. We wanted to scrutinize whether a hypothesized enhanced primary production along the ice edges would reflect upon benthic biomass. Within the peracarid community a total of 14,784 individuals were collected at these locations, while an additional 2,425 specimens were sampled at a 500-m station at 79°N, in an area where samples had been also taken in 1993. For reasons of comparison, numbers of peracarids found at any one station were calculated for 1,000-m trawled distance. These calculations accounted for 55,633 specimens on both transects. Of these, the order Isopoda was the most numerous taxon with 28,650 specimens, followed by the Amphipoda with 15,025 specimens, Cumacea with 7,868, Tanaidacea with 2,454 and the suprabenthic Mysidacea with 1,636 individuals collected at all stations during this expedition, respectively. Interestingly the highest number of individuals was sampled at 1,525-depth (23,098 individuals); however, at about 2,680-m depth the number of peracarids collected (13,557) was still much higher than at comparatively shallower stations, for example, in 317-m depth (6,792). Possible reasons for these findings are discussed.
83689740
Distribution, abundance, biomass, and mineralization potential of the epibenthic megafauna of the Northeast Greenland shelf
The epibenthic megafauna of the high-Arctic Northeast Greenland shelf was investigated by means of seafloor photography and Agassiz trawl catches. At 54 stations in water depths between 40 and 770 m, sequences of color slides, each depicting about 1 m2 of the seafloor, were obtained along photographic transects of about 100 to 600 m length. The photographs were quantitatively analyzed for abundance of epibenthic organisms identified by comparison with specimens collected from trawl catches. Megabenthic biomass was estimated by multiplying density values with averge body mass figures. For five dominant brittle star species, the population oxygen uptake and, thus, organic carbon mineralization potential were approximated by applying individual respiration rates of average-sized specimens to density figures. Multivariate analyses of the megabenthic species distribution revealed a distinct depth zonation. Shallow shelf banks (<150 m), characterized by coarse sediments, many stones and boulders as well as negative bottom water temperatures, housed a rich epifauna (30 to 340 ind m−2, 1.8 to 10.5 g AFDW m−2), strongly dominated (80 to 98% by numbers) by the brittle stars Ophiocten sericeum and Ophiura robusta. The oxygen uptake by brittle stars ranged from 0.4 to 95 μmol O2 m−2 h−1 (i.e., assuming a respiratory quotient of 0.8, an organic carbon mineralization of 0.1 to 21.9 mg C m−2 d−1). At the bank flanks sloping to the shelf troughs (100 to 580 m), finer sediments prevailed, stones were rare, and bottom water temperatures were positive due to the inflow of Atlantic water. Compared to bank sites, total epibenthic abundances as well as carbon mineralization by brittle stars were roughly ten times and total biomass about four times smaller. In deep shelf depressions as well as at the continental slope (200 to 770 m), stones were completely lacking, and sediments very fine. Epibenthic standing stock and carbon mineralization were one to two orders of magnitude lower than on the banks. The estimation of brittle star oxygen uptake indicates that a considerable portion of the organic carbon produced in the polynya and partitioned to the benthos may be remineralized by epibenthic bank assemblages.
140601053
Summer distribution and ecological role of seabirds and marine mammals in the Norwegian and Greenland seas (June 1988)
Abstract During the ARK V /2 expedition of RV Polarstern in the Norwegian and Greenland seas in June 1988, 380 half hour counts for marine vertebrates (seabirds, pinnipeds and cetaceans) were carried out. Results are presented as total numbers encountered and then converted into density and food intake. Mean food intake was 2.2 kg fresh weight per km2 per day for seabirds, with a higher value in Atlantic water (2.5) lower values in polar water and the pack ice (1.7 and 1.9), and an intermediate value at the ice edge. The main species were the alcids (1.5, primarily Little Auk, Alle alle and Brunnich's Guillemot, Urea Iomvia) ,the Fulmar, Fulmarus glacialis (0.5), and the Kittiwake, Rissa tridactyla (0.2). The ecological role of cetaceans was clearly lower, with a mean value of 0.2 and a maximum of 0.7 in Atlantic water (rough evaluation, due to the low number of contacts). The food intake by pinnipeds was 0.55 kg/km2 day at the ice edge and 0.4 in the pack ice; they were mainly harp, Phoca groenlandica and hooded seals, Cystophora cristata, in one main concentration each and ringed seals, Phoca hispida, scattered on the pack. Data for July 1988 show a great similarity with these results, except for a lower density of alcids, which probably reflects that Little Auk, Brunnich's Guillemot and Common Guillemot, Uria aalge already had started to leave the region.
39180046
Summer at-sea distribution of little auks Alle alle and harp seals Pagophilus (Phoca) groenlandica in the Fram Strait and the Greenland Sea: impact of small-scale hydrological events
Among the most numerous seabird and pinniped species of the Fram Strait and the Greenland Sea, little auks Alle alle and harp seals Pagophila (Phoca) groenlandica are very abundant in the mixed Polar/Arctic Waters at the front between the two water masses. This must reflect the presence of very high concentrations of their food, Arctic zooplankton and nekton, massively attracting their predators. Such a high biological production seems to be depending on new primary production based on upwelling and high nutrient concentration. This usually takes place at the ice edge (e.g. July 2005), but hydrological conditions such as eddies can modify its position, east of the front in open water as caused by a subsurface eddy (August 2005), or in ice-covered areas if westerly winds push the pack ice to the east, eventually covering an eddy and causing very high concentrations of little auks and harp seals (July 2008). On the other hand, a dramatic decrease of pack ice coverage can move this water mass farther north and west, making it inaccessible to little auks during their breeding season, and apparently causing breeding failure in Jan Mayen in July 2005. In future years, if a much stronger diminution in sea ice coverage will take place, similar to the retreat in 2005 and 2007, the failure might affect the whole Spitsbergen population, as well as other seabird species feeding mainly at the ice edge.
86780562
Estimation of harp seal (Pagophilus groenlandicus) pup production in the North Atlantic completed: results from surveys in the Greenland Sea in 2002
From 14 March to 6 April 2002 aerial surveys were carried out in the Greenland Sea pack ice (referred to as the “West Ice”), to assess the pup production of the Greenland Sea population of harp seals, Pagophilus groenlandicus. One fixed-wing twin-engined aircraft was used for reconnaissance flights and photographic strip transect surveys of the whelping patches once they had been located and identified. A helicopter assisted in the reconnaissance flights, and was used subsequently to fly visual strip transect surveys over the whelping patches. The helicopter was also used to collect data for estimating the distribution of births over time. Three harp seal breeding patches (A, B, and C) were located and surveyed either visually or photographically. Results from the staging flights suggest that the majority of harp seal females in the Greenland Sea whelped between 16 and 21 March. The calculated temporal distribution of births were used to correct the estimates obtained for Patch B. No correction was considered necessary for Patch A. No staging was performed in Patch C; the estimate obtained for this patch may, therefore, be slightly negatively biased. The total estimate of pup production, including the visual survey of Patch A, both visual and photographic surveys of Patch B, and photographic survey of Patch C, was 98 500 (s.e. = 16 800), giving a coefficient of variation of 17.9% for the survey. Adding the obtained Greenland Sea pup production estimate to recent estimates obtained using similar methods in the Northwest Atlantic (in 1999) and in the Barents Sea/White Sea (in 2002), it appears that the entire North Atlantic harp seal pup production, as determined at the turn of the century, is at least 1.4 million animals per year.
1751301
Nitrogen uptake in two frontal areas in the Greenland Sea
SummaryDuring late spring, 1987, observations were made of nitrate and ammonium uptake in two regions of the Greenland Sea, the Arctic Front and the Polar Front. In the area of the Arctic Front, mixed layers were relatively deep (generally below 100m), and the 1% isolume averaged 35 m. Ambient nitrate concentrations were always greater than 6 μM, whereas ammonium levels were always less than 0.6 μM. Surface nitrate and ammonium specific uptake rates averages 4.4 and 2.3×10−3 h−1, respectively. The Polar Front generally coincided spatially with the location of the ice edge, and vertical mixed layers were shallow (pycnocline depth ranged from 8–14 m), and the 1 % isolume averaged 37 m. Nitrate concentrations were somewhat lower than in the Arctic Front, but remained above 3 μM at all times. Ammonium levels reached 1.2 μM. Nitrate and ammonium specific uptake rates at the surface averaged 4.8×10−3 and 10×10−3 h−1, respectively. Integrated water column f-ratios for the Arctic and Polar Front regions averaged 0.63 and 0.31, and the ammonium relative preference indices at all depths within each study area were always greater than 8, indicating that ammonium remained the preferred nitrogen source for phytoplankton. New production in the two regions was approximately equal, but the Polar Front had a substantially greater amount of regenerated production, and hence total production as well. Irradiance (and not nutrient concentration) seems to be the most important environmental factor in controlling nitrogen uptake. The spatial variability observed within the Greenland Sea suggest that inclusion of this region in global carbon models will require increased spatial resolution of both the models and the data included.
128534794
New Production in the Northeast Water Polynya: 1993
The Northeast Water Polynya has been suggested as acting as a sink for carbon, especially during the spring and summer when phytoplankton growth is active. During 1993 the polynya was sampled for the entire growing period (late May through mid-August) in order to more accurately assess the magnitude, controls and patterns of new and total (ammonium, nitrate and urea) nitrogen production. This represents the first assessment of new production throughout an entire season in the Arctic. We found that, in 1993, new production, based on 15N-tracer techniques and integrated over the euphotic zone, was 0.141 mmol N m−2 h−1 (0.361 g C m−2 d−1 when converted using observed C/N ratios). Measured f ratios averaged 0.65 and demonstrate that the system, to a great extent, was using nitrate as a nitrogen source. In general f ratios were greatest early in the season and minimal in mid-summer. Urea uptake was highly variable and contributed slightly less than ammonium to phytoplankton nitrogen demand. Nitrate uptake at stations with low (< 0.5μM) nitrate concentrations was significantly reduced, implying that nitrate concentrations limited phytoplankton growth late in the growing season. Long-term new production rates calculated from nutrient depletion patterns from the polynya as a whole as well as a time-series constructed from a single location were ca. 0.144-0.281 g C m−2 d−1. The relationship between new production as measured by incubations and nutrient depletion budgets suggests that phytoplankton growth is the dominant factor influencing the nitrogen budget of the polynya. The amount of material available for removal from the euphotic zone is limited and constrains the degree to which the polynya can act as a regional carbon sink.
54697118
Environmental forcing of phytoplankton community structure and function in the Canadian High Arctic: contrasting oligotrophic and eutrophic regions
We assessed phytoplankton dynamics and its environmental control across the Canadian High Arctic (CHA). Environmental (hydrographic, atmospheric, sea ice conditions) and biological variables (phytoplankton production, biomass, composition) were measured along 3500 km transects across the Beaufort Sea, the Canadian Arctic Archipelago, and Baffin Bay during late summer 2005, early fall 2006 and fall 2007. Phytoplankton production and chlorophyll a (chl a) biomass were measured at 7 optical depths, including the depth of subsurface chl a maximum (ZSCM). Phytoplankton taxonomy, abundance, and size structure were determined at the ZSCM. Redundancy analyses and non-metric multidimensional scaling were used to assess relationships between phytoplankton composition in relation to biological and environmental variables. In late summer/fall, the CHA was characterized by (1) an oligotrophic flagellate-based system extending over the eastern Beaufort Sea, the peripheral Amundsen Gulf, and the central region of the Canadian Arctic Archipelago; and (2) a eutrophic diatom-based system located in Baffin Bay, Lancaster Sound, and in a hotspot in the central Amundsen Gulf. The oligotrophic regions were characterized by low production and biomass of large phytoplankton cells (>5 μm) and relatively high abundance of eukaryotic picophytoplankton (<2 μm) and unidentified nanoflagellates (2−20 μm). The eutrophic regions were characterized by high production and biomass of large cells and relatively high abundance of centric diatoms, mainly Chaetoceros spp. The distinction between the 2 regimes was explained by differences in stratification (density gradient) and nitrate concentrations at the ZSCM. This study demonstrates the key role of vertical mixing and nutrient input in shaping the structure and function of phytoplankton communities in the CHA, showing how ongoing environmental changes have the capacity to alter the diversity of biogeographic regions in the CHA.
128932493
Distribution and composition of suspended biogenic particles in surface waters across Subarctic and Arctic Seas
[1] Suspended biogenic particles were examined across Subarctic and Arctic Seas during the Canada-Three-Oceans (C3O) program in the summers of 2007 and 2008. Particulate organic carbon (POC) and nitrogen (PON), biogenic silica (bSiO2), and size-fractionated chlorophyll a (chl a) concentrations were measured within the euphotic zone throughout five domains: Eastern Subarctic North Pacific (ESNP), Bering and Chukchi Seas (BE-CH), Southern Beaufort Sea and Canada Basin (BS-CB), Canadian Arctic Archipelago (CAA), and Baffin Bay and Labrador Sea (BB-LS). Despite large variability along the sampling transect and vertically throughout the euphotic zone, domain averages of depth-integrated POC and PON were relatively invariant across the ESNP, BE-CH, CAA, and BB-LS, ranging from 546 to 670 mmol m−2 (POC) and 101 to 154 mmol m−2 (PON), but were much lower in BS-CB (199 and 78 mmol m−2, respectively). In contrast, depth-integrated bSiO2 averages were highest in BE-CH and CAA (>100 mmol m−2), intermediate in ESNP and BB-LS (34–48 mmol m−2), and low in BS-CB (6 mmol m−2). Similarly to the bSiO2 distribution, the biomass of the >5 μm chl a size-fraction averaged 68–69% of total chl a in BE-CH and CAA, 56% in BB-LS, and 22–23% in ESNP and BS-CB. Ratios of bSiO2:PON averaged 1.10–1.30 in BE-CH and CAA, 0.30–0.34 in ESNP and BB-LS, and 0.08 in BS-CB. This study highlights the relative importance of siliceous phytoplankton such as diatoms in BE-CH and CAA, smaller nonsiliceous cells in BS-CB and ESNP, and a mixed assemblage of variably sized phytoplankton with a less siliceous component in BB-LS.
129031232
Effects of future climate change on primary productivity and export fluxes in the Beaufort Sea
[1] We present projections of future primary production for the Canadian Beaufort Shelf of the Arctic Ocean, using simulations of future climate change from the Canadian Global Climate Model (CGCM2) to force a coupled sea ice-ocean-biological one-dimensional model. We compare three 18 year simulations, 1975–1992, 2042–2059, and 2082–2099, to describe the impacts of a reduction in sea ice cover duration and thickness and an increase in surface freshwater fluxes. Our results show an increase in average annual primary production of 6% between the period 1975–1992 and the period 2042–2059 and an increase of 9% between 1975–1992 and 2082–2099. The relative contribution of the ice algal and spring phytoplankton blooms to the annual primary production is reduced in the future runs owing to a reduction in the length of the ice algal growth season (resulting from earlier snow and ice melt) and to a reduction in the replenishment of nutrient to the mixed layer in winter. The duration of the summer subsurface phytoplankton bloom increases, which favors the development of the main copepod species and leads to an increase in export production (16% between 1975–1992 and 2082–2099) that is greater than the increase in primary production.
86754862
Prevalence, structure and properties of subsurface chlorophyll maxima in Canadian Arctic waters
Comprehensive investigations of the Canadian Arctic during late summer and early fall revealed the widespread occurrence of long-lived subsurface chlorophyll maxima (SCM) in season- ally ice-free waters. The vertical position of the SCM corresponded with the depth of the subsurface biomass maximum (SBM), at least in Baffin Bay, suggesting that SCM could be an important source of carbon for the food web. Most of these SCM were located well below the pycnocline in close association with the nitracline, implying that their vertical position was driven mainly by a shortage of inorganic nitrogen in the upper euphotic zone. The diversity of SCM configurations with respect to physical properties of the water column complicates the estimation of euphotic-zone chlorophyll and primary production from surface properties. High photosynthetic yields (Fv/Fm) showed the phyto- plankton to be photosynthetically competent and well acclimated to conditions of irradiance and nutrient supply near the surface and at the SCM. A well-defined primary nitrite maximum was associated with the SCM in the southwest Canadian Arctic, but not in the northeast where nitrite concentrations were highest much below the euphotic zone. This contrast is consistent with differences in vertical stratification, the light-dark cycle and, possibly, the physiological state and taxonomic composition of the phytoplankton community at the SCM. This study demonstrates that the SCM, once regarded as anecdotal due to under-sampling, are a dominant feature of the Arctic Ocean that should be considered in remote sensing studies and biogeochemical models.
129729499
Synthesis of integrated primary production in the Arctic Ocean: II. In situ and remotely sensed estimates
Abstract Recent warming of surface waters, accompanied by reduced ice thickness and extent may have significant consequences for climate-driven changes of primary production (PP) in the Arctic Ocean (AO). However, it has been difficult to obtain a robust benchmark estimate of pan-Arctic PP necessary for evaluating change. This paper provides an estimate of pan-Arctic PP prior to significant warming from a synthetic analysis of the ARCSS-PP database of in situ measurements collected from 1954 to 2007 and estimates derived from satellite-based observations from 1998 to 2007. Vertical profiles of in situ chlorophyll a (Chl a ) and PP revealed persistent subsurface peaks in biomass and PP throughout the AO during most of the summer period. This was contradictory with the commonly assumed exponential decrease in PP with depth on which prior satellite-derived estimates were based. As remotely sensed Chl a was not a good predictor of integrated water column Chl a , accurate satellite-based modeling of vertically integrated primary production (IPP sat ), requires knowledge of the subsurface distribution of phytoplankton, coincident with the remotely sensed ocean color measurements. We developed an alternative approach to modeling PP from satellite observations by incorporating climatological information on the depths of the euphotic zone and the mixed layer that control the distribution of phytoplankton that significantly improved the fidelity of satellite derived PP to in situ observations. The annual IPP of the Arctic Ocean combining both in situ and satellite based estimates was calculated here to be a minimum of 466 ± 94 Tg C yr −1 and a maximum of 993 ± 94 Tg C yr −1 , when corrected for subsurface production. Inflow shelf seas account for 75% of annual IPP, while the central basin and Beaufort northern sea were the regions with the lowest annual integrated productivity, due to persistently stratified, oligotrophic and ice-covered conditions. Although the expansion of summertime ice retreat should stimulate photosynthesis by exposing more of the AO to solar irradiance, total PP is ultimately limited by nutrient availability. Therefore, changes in AO PP will be forced by the balance between stratification and mixing, the effects of which are not yet quantified.
18418493
An annual study of inorganic and organic nitrogen and phosphorus and silicic acid in the southeastern Beaufort Sea
[1] Water column samples from the Mackenzie Shelf, the Beaufort Sea, and the Amundsen Gulf were obtained during 2003–2004 to investigate nutrient dynamics in an Arctic ecosystem influenced by a large river and flaw lead polynya. Nutrient inventories in the upper water column showed a significant seasonal drawdown of nitrate (NO3−) and silicic acid (Si(OH)4) (1:1.75 mol/mol) and subsequent accumulation of nitrite (NO2−) and ammonium (NH4+). Dissolved organic nitrogen and phosphorus concentrations (DON and DOP) were elevated in surface waters during the time of peak phytoplankton growth (bloom and postbloom phases) and covaried in a 17:1 molar ratio. Vertical profiles showed the typical middepth maxima in NO3−, PO43−, and Si(OH)4 at salinity 32–33.1. The concentration of DOP (0.76 ± 0.27 μmol P L−1) was also 2 times higher in this layer compared to the surface average and inversely correlated with the water mass tracer N* [N* = (NO3− − 16 × PO43− + 2.9) × 0.87], suggesting that Pacific-derived waters were a source of the enrichment. Below the mixed layer, DON was generally constant with depth, although averaged profiles (like those of urea) suggested the presence of subsurface maxima at 50 m and between 250 and 300 m. Regeneration ratios varied with depth and were approximately 9.0 mol −O2/mol NO3− and 122.5 mol −O2/mol PO43− in shallow Pacific-derived waters (halocline layer) and 17.4 and 193.5 in deep Atlantic waters (Atlantic layer), respectively. Deep waters of the Amundsen Gulf contained an excess of 1.7 μmol NO3− L−1, 0.12 μmol PO43− L−1, and 6.2 μmol Si(OH)4 L−1 and a deficit in O2, relative to waters of similar density in the Beaufort Sea, in proportions consistent with the remineralization ratios derived from oxygen-nutrient regressions. Enhanced export of particulate matter from the overlying polynya and subsequent remineralization at depth are hypothesized to create this nutrient enrichment.
55739595
Climatic and biological forcing of the vertical flux of biogenic particles under seasonal Arctic sea ice
ABSTRACT: Ice algae, phytoplankton, zooplankton and the vertical fluxes of chloropigments andparticulate organic carbon (POC) were monitored from May to June/July of 1992, 1994 and 1995under the ice of Barrow Strait (Canadian Arctic Archipelago). Large interannual differences in thetiming, magnitude and nature of vertical fluxes were driven by meteorological events that controlledsnow cover and by differences in zooplankton assemblages. In 1992, ice algae released from the icematrix were intensely recycled by the exceptionally abundant calanoid Pseudocalanus acuspes . Thepersistent snow cover delayed the phytoplankton bloom until after the ice break-up in July. Ice algaewere abruptly released and sank rapidly to depth following early rain in late May 1994 and a heat-wave in early June 1995. In both years, the early removal of snow triggered an under-ice phyto-plankton bloom and strong downward fluxes of POC and chloropigments (13.7 gC m –2 , 381 mgchloropigments m –2 in 1994). In the absence of nutrient limitation, under-ice fluxes represented anet addition to the annual flux of POC. The analysis of local climate from 1950 to 1995 suggests thatstrong and early under-ice fluxes of biogenic carbon in spring may become more frequent under theclimatic conditions anticipated by general circulation models.KEY WORDS: Sea ice · Carbon flux · Climate forcing · Copepod grazing · Arctic
129789530
Variability in oceanographic and ecological processes in the Canadian Arctic Archipelago
This paper brings together unpublished historical data sets and published literature to review the role of climatic, oceanographic and ecological processes in the marine ecosystem of the eastern Canadian Archipelago. Physical data include characteristics of the water masses, circulation patterns, sea ice conditions, and climatic records from 1950s onward. Biological data include unpublished data sets on nutrients, primary and secondary production, and sedimentation, which were collected during the 1980–1990s in the eastern Canadian Archipelago. These results show high year-to-year variability in nutrient inventories and ratios, the magnitude of the ice algae and phytoplankton bloom, the timing of ice algae sedimentation in the spring, and the composition of the zooplankton community. The significance of this high interannual variability and its effect on pelagic–benthic coupling processes is discussed in the context of climatic and oceanographic forcing, with emphasis on recent (past decade) Arctic changes. An estimate of total primary production in the Archipelago is also presented, along with published production estimates for other Arctic shelves, showing that the Archipelago may support up to 32% of the total primary production of Arctic shelves. The high year-to-year variability in production and carbon transfer pathways (e.g. pelagic versus benthic) in the Archipelago suggest that the system might be resilient to the increased variability in climatic conditions occurring in the past decade. However, this increased variability combined with directional change in climatic and oceanographic conditions might also modify the existing balance of ecological processes. For example, shifts in the timing of events appear to have already occurred in the past decade, with potential cascading effects throughout the ecosystem.
128874051
Recent Arctic Ocean sea ice loss triggers novel fall phytoplankton blooms
Recent receding of the ice pack allows more sunlight to penetrate into the Arctic Ocean, enhancing productivity of a single annual phytoplankton bloom. Increasing river runoff may, however, enhance the yet pronounced upper ocean stratification and prevent any significant wind-driven vertical mixing and upward supply of nutrients, counteracting the additional light available to phytoplankton. Vertical mixing of the upper ocean is the key process that will determine the fate of marine Arctic ecosystems. Here we reveal an unexpected consequence of the Arctic ice loss: regions are now developing a second bloom in the fall, which coincides with delayed freezeup and increased exposure of the sea surface to wind stress. This implies that wind-driven vertical mixing during fall is indeed significant, at least enough to promote further primary production. The Arctic Ocean seems to be experiencing a fundamental shift from a polar to a temperate mode, which is likely to alter the marine ecosystem.
59037253
Seasonal contributions of phytoplankton and fecal pellets to the organic carbon sinking flux in the North Water (northern Baffin Bay)
The downward export of organic material was assessed during the productive period (late spring to early autumn) in the North Water polynya area (NOW; northern Baffin Bay). Free- drifting short-term particle interceptor traps were deployed at 3 depths below the euphotic zone (50, 100 and 150 m) for 12 to 24 h at 19 stations from June to July in 1998 and at 12 stations during August and September in 1999. The sinking material was analyzed for particulate organic carbon (POC) and pigments (chlorophyll a and pheopigments), and for phytoplankton and fecal pellet enumerations. POC and pigment sinking fluxes at 50 m averaged 337 and 8 mg m -2 d -1 , respectively. The maximum sinking fluxes of organic matter (ca. 554 mg C m -2 d -1 and 14 mg pigments m -2 d -1 ) were observed in June, after which they decreased and remained relatively constant (ca. 219 to 240 mg C m -2 d -1 and 3.9 to 4.1 mg pigments m -2 d -1 ). Phytoplankton carbon flux decreased while fecal carbon flux increased during the study. In June, intact diatom cells and fecal pellets made up 50 and 4% of the total POC sinking flux, respectively. During the following months, they made up ≤10% (diatoms) and 30 to 50% (fecal pellets) of the total POC flux. A rapid increase in sinking cell numbers and fecal pellets at the end of the sampling season points to a late summer-early autumn bloom in the NOW. The dominant pathway of carbon cycling changed during the study, from export in spring to reten- tion afterwards. From July on, the retention of particulate organic matter in the upper 100 m of the water column was favored by the low sinking velocities of POC and chlorophyll a, which averaged ≤1. 3md -1 . Over the whole sampling period, 35% of the particulate phytoplankton production was exported through sinking, while 65% was recycled or remained suspended in the euphotic zone. The organic carbon produced in the euphotic zone was, thus, mainly available to pelagic grazers rather than being exported to the benthic community. These results are in agreement with the abundance of higher trophic level pelagic organisms observed in this region.
128826281
The annual cycle of particulate organic carbon export in Franklin Bay (Canadian Arctic): Environmental control and food web implications
[1] As part of the Canadian Arctic Shelf Exchange Study (CASES), we assessed the importance of new production and resuspension in determining the nature and magnitude of the deep (210 m) particulate organic carbon (POC) flux from October 2003 to September 2004 in central Franklin Bay. In spring and summer, phytoplankton production was nutrient-limited in the stratified surface layer and the initial spring bloom evolved into a subsurface chlorophyll maximum (SCM) at the nutricline. Large herbivorous calanoid copepods intercepted little of the initial bloom but grazed intensely on the SCM. The phytoplankton and fecal pellet fluxes culminated simultaneously in July–August (24 and 23 mg C m−2 d−1, respectively). The detrital POC flux peaked in September (52 mg C m−2 d−1), coincident with wind-induced resuspension of recently settled POC. In the fall, detrital POC fluxes increased again to 22 mg C m−2 d−1, following the off-shelf transport of terrigenous POC carried by the Mackenzie River plume and POC resuspended by wind on the shelf. In winter, the relatively weak POC fluxes (2–7 mg C m−2 d−1, detrital at 90%) resulted from the settling down of resuspended sediments. We propose a conceptual model in which the ecosystem of Franklin Bay shifts from an algal to a detrital mode according to seasonal changes in the relative importance of fresh and old POC supplies. On the basis of this model, the ecosystem of southeastern Beaufort Sea could evolve toward a less productive equilibrium dominated by sediment resuspension in response to the ongoing reduction of the ice cover.
42068843
The spatial distribution of solar radiation under a melting Arctic sea ice cover
[1] The sea ice cover of the Chukchi and Beaufort Seas is currently undergoing a fundamental shift from multiyear ice to first-year ice. Field observations of sea ice physical and optical properties were collected in this region during June–July 2010, revealing unexpectedly complex spatial distributions of solar radiation under the melt-season ice cover. Based on our optical measurements of first-year ice, we found the under-ice light field in the upper ocean to be spatially heterogeneous and dependent on wavelength, ice thickness, and the areal and geometric distribution of melt ponded and bare ice surfaces. Much of the observed complexity in radiation fields arose because the transmission of light through ponded ice was generally an order of magnitude greater than through bare, unponded ice. Furthermore, while many sites exhibited a consistent, exponential decay in light transmission through both ponded and bare ice surfaces, light transmission under bare ice was also observed to increase with depth (reaching maximum values ∼5–10 m below the bottom of the ice). A simple geometric model shows these transmission peaks are a result of scattering in the ice and the interspersion of bare and ponded sea ice surfaces. These new observations of complex radiation fields beneath melt-season first-year sea ice have significant implications for biological production, biogeochemical processes, and the heat balance of sea ice and under-ice ocean waters and should be carefully considered when modeling these sea ice-related phenomena.
41193464
Albedo evolution of seasonal Arctic sea ice
[1] There is an ongoing shift in the Arctic sea ice cover from multiyear ice to seasonal ice. Here we examine the impact of this shift on sea ice albedo. Our analysis of observations from four years of field experiments indicates that seasonal ice undergoes an albedo evolution with seven phases; cold snow, melting snow, pond formation, pond drainage, pond evolution, open water, and freezeup. Once surface ice melt begins, seasonal ice albedos are consistently less than albedos for multiyear ice resulting in more solar heat absorbed in the ice and transmitted to the ocean. The shift from a multiyear to seasonal ice cover has significant implications for the heat and mass budget of the ice and for primary productivity in the upper ocean. There will be enhanced melting of the ice cover and an increase in the amount of sunlight available in the upper ocean.
67802281
The isotopic signature of particulate organic C and N in bottom ice: Key influencing factors and applications for tracing the fate of ice-algae in the Arctic Ocean
[1] The isotopic, taxonomic, and nutrient dynamics of protist communities at the bottom of first-year sea ice were studied for a wide range of ice conditions during the spring-summer transition in the southeast Beaufort Sea. In bottom ice, total protist abundance ranged from 0.07 to 9.94 × 109 cells m–2 and chlorophyll a biomass ranged from 0.33 to 110 mg m–2. Both variables were positively related to the concentrations of nitrate, silicic acid, and phosphate at the ice-water interface, with r2 values between 0.63 and 0.79. Results showed that the δ13C of sympagic (ice-associated) particulate organic matter (POM) (–27.1 to –11.4‰) was mainly influenced by ice protist stocks and dissolved inorganic carbon availability. Flagellated cells maintained a low δ13C relative to diatoms. The δ15N of POM (3.9 to 9.4‰) could not be explained by any of the variables considered and showed considerable overlap with the pelagic δ15N-POM (0.0 to 10.3‰). Detailed analyses of δ13C-POM through size fractionation and settling experiments along with a short temporal study of the interaction between sympagic and pelagic communities confirmed or demonstrated that (1) the analysis of stable C isotopes is a valuable tool to trace the flow of ice-derived matter, (2) sympagic POM contributes substantially to suspended pelagic biomass during release episodes, and (3) ice-grown autotrophic flagellated cells have a strong potential to interact with the pelagic biota in the coastal Arctic Ocean. This study highlights the need to carefully evaluate stable isotope dynamics before assessing food web interactions or the fate of POM in seasonally ice-covered waters.
128901169
Photosynthetic characteristics of sinking microalgae under the sea ice
The photosynthetic characteristics of sinking a microalgal community were studied to compare with the ice algal community in the sea ice and the phytoplankton community in the water column under the sea ice at the beginning of the light season in the first-year sea ice ecosystem on the Mackenzie Shelf, in the western Canadian Arctic. The phytoplankton community was collected using a water bottle, whereas the sinking algal community was collected using particle collectors, and the ice algal community was obtained by using an ice-core sampler from the bottom portion of ice core. Photosynthesis versus irradiance (P-E) incubation experiments were conducted on deck to obtain the initial slope (αB) and the maximum photosynthetic rate (PmB) of the three algal communities. The αB and the PmB of the light saturation curve, and chlorophyll a (Chl a) specific absorption coefficient (āph*) between the sinking microalgal community and the ice algal community were similar and were distinctly different from the phytoplankton community. The significant linear relationship between αB and PmB, which was obtained among the three groups, may suggest that a photo-acclimation strategy is common for all algal communities under the low light regime of the early season. Although the sinking algal community could be held for the entire duration of deployment at maximum, this community remained photosynthetically active once exposed to light. This response suggests that sinking algal communities can be the seed population, which results in a subsequent phytoplankton bloom under the sea ice or in a surface layer, as well as representing food for the higher trophic level consumers in the Arctic Ocean even before the receding of the sea ice.
53539005
Dark-Season Survival Strategies of Coastal Zone Zooplankton in the Canadian Arctic
For herbivorous zooplankton, surviving the arctic winter requires that sufficient energy be stored in summer to enable ten months or more of possible starvation. Energy and materials for reproduction may also be totally derived from stored lipid and bodily protein. The predominant storage products are wax esters, often visible as translucent droplets or a fusiform inclusion in the tissues. Lipid may constitute more than 50% of dry weight at the end of summer. Reproduction is synchronized with season and environmental conditions to enable offspring to exploit the brief period of intense primary production. So far as we know, fertilization occurs only once in the copepods studied here, which make up more than 98% of the total zooplankton by numbers, and males are short lived, but in one species ( Calanus hyperboreus ) females may survive into a second productive season, thereby storing sufficient reserves to spawn a second time. Several plaktonic species, including larval invertebrates, start growth early by utilizing algae that develop on the under-ice surface serveral months before the pelagic phytoplankton bloom. The minimum water temperature (-1.8 C) is constant and much warmer than the atmosphere, so overwintering should be less stressful for aquatic species than for terrestrial forms. Additional adaptations used by zooplankton in winter include seeking deeper water to escape predation, reducing swimming costs by regulating buoyancy, and further lowering metabolic rates by limiting synthesis of enzymes and increasing the fraction of lipid used in respiration. Key words: copepods, zooplankton, phytoplankton, ice-algae, fast ice, lipid, overwintering, survival strategies, growth, reproduction
128675095
Seasonal food web structures and sympagic–pelagic coupling in the European Arctic revealed by stable isotopes and a two-source food web model
Abstract We simultaneously followed stable carbon (δ13C) and nitrogen (δ15N) isotopes in a two-source food web model to determine trophic levels and the relative importance of open water- and ice-associated food sources (phytoplankton vs. ice algae) in the lower marine food web in the European Arctic during four seasons. The model is based upon extensive seasonal data from 1995 to 2001. Phytoplankton, represented by samples of particulate organic matter from open water (Pelagic-POM) and ice algae, represented by samples from the underside of the ice (Ice-POM), were isotopically different. Ice-POM was generally dominated by the typical ice diatoms Nitzschia frigida and Melosira arctica and was more enriched than Pelagic-POM in 13C (δ13C = −20‰ vs. −24‰), but less enriched in 15N (δ15N = 1.8‰ vs. 4.0‰). However, when dominated by pelagic algae, Ice-POM was enriched in 13C and 15N similarly to Pelagic-POM. The derived trophic enrichment factors for δ15N (ΔN = 3.4‰) and δ13C (ΔC = 0.6‰) were similar in both pelagic and sympagic (ice-associated) systems, although the ΔC for the sympagic system was variable. Trophic level (TL) range for zooplankton (TL = 1.8–3.8) was similar to that of ice fauna (TL = 1.9–3.7), but ice amphipods were generally less enriched in δ15N than zooplankton, reflecting lower δ15N in Ice-POM compared to Pelagic-POM. For bulk zooplankton, TLs and carbon sources changed little seasonally, but the proportion of herbivores was higher during May–September than in October and March. Overall, we found that the primary carbon source for zooplankton was Pelagic-POM (mean 74%), but depending on species, season and TL, substantial carbon (up to 50%) was supplied from the sympagic system. For bulk ice fauna, no major changes were found in TLs or carbon sources from summer to autumn. The primary carbon source for ice fauna was Ice-POM (mean 67%), although ice fauna with TL > 3 (adult Onisimus nanseni and juvenile polar cod) primarily utilized a pelagic food source.
85430549
Seasonal feeding strategies of Calanus in the high-Arctic Svalbard region
Abstract The feeding strategies of Calanus hyperboreus, C. glacialis, and C. finmarchicus were investigated in the high-Arctic Svalbard region (77–81 °N) in May, August, and December, including seasons with algal blooms, late- to post-bloom situations, and unproductive winter periods. Stable isotope and fatty acid trophic marker (FATM) techniques were employed together to assess trophic level (TL), carbon sources (phytoplankton vs. ice algae), and diet of the three Calanus species. In addition, population development, distribution, and nutritional state (i.e. storage lipids) were examined to estimate their population status at the time of sampling. In May and August, the vertical distribution of the three Calanus species usually coincided with the maximum algal biomass. Their stable isotope and fatty acid (FA) composition indicated that they all were essentially herbivores in May, when the algal biomass was highest. Their FA composition, however, revealed different food preferences. C. hyperboreus had high proportions of 18:4n3, suggesting that it fed mainly on Phaeocystis, whereas C. glacialis and C. finmarchicus had high proportions of 16:4n1, 16:1n7, and 20:5n3, suggesting diatoms as their major food source. Carbon sources (i.e. phytoplankton vs. ice algae) were not possible to determine solely from FATM techniques since ice-diatoms and pelagic-diatoms were characterised by the same FA. However, the enriched δ13C values of C. glacialis and C. finmarchicus in May indicated that they fed both on pelagic- and ice-diatoms. Patterns in absolute FA and fatty alcohol composition revealed that diatoms were the most important food for C. hyperboreus and C. glacialis, followed by Phaeocystis, whereas diatoms, Phaeocystis and other small autotrophic flagellates were equally important food for C. finmarchicus. During periods of lower algal biomass, only C. glacialis exhibited evidence of significant dietary switch, with a TL indicative of omnivory (mean TL=2.4). Large spatial variability was observed in population development, distribution, and lipid store sizes in August. At the northernmost station at the southern margin of the Arctic Ocean, the three Calanus species had similarly low lipid stores as they had in May, suggesting that they ascended later in the year. In December, relatively lipid-rich specimens had TL similar to those during the peak productive season (TL≈2.0), suggesting that they were hibernating and not feeding on the available refractory material available at that time of the year. In contrast, lipid-poor specimens in December had substantially high TL (TL=2.5), suggesting that they were active and possibly were feeding.
128667553
Consequences of changing sea-ice cover for primary and secondary producers in the European Arctic shelf seas: Timing, quantity, and quality
The Arctic ice cover poses severe limitations on the productive period of marine autotrophs that form the base of the marine food web. Sea-ice algae begin to grow in early spring within and underneath the ice, producing a substantial biomass despite very low light intensities. Pelagic algal blooms, in contrast, normally occur after ice breakup, at high latitudes as late as July–September. The timing of these blooms is crucial for the quantity and quality of primary and secondary production, and therefore for the transfer of energy and matter to higher trophic levels. Recent findings from Rijpfjorden, north-eastern Svalbard indicate that ice algae, rather than pelagic algae, trigger the reproduction of Arctic zooplankton around Svalbard. The key herbivore in Arctic shelf seas, the copepod Calanus glacialis, timed its seasonal migration, foraging, and reproduction to the ice algal bloom, which preceded the pelagic algal bloom by two months. The growth of this secondary producer’s offspring, however, was dependent on the later bloom of phytoplankton and higher sea-water temperatures. In 2007, reproduction and growth of C. glacialis and the primary production regime matched perfectly. The persistent ice cover in summer 2008, however, led to a mismatch between the pelagic algal bloom and the growth of the new copepod generation, resulting in a fivefold lower biomass of C. glacialis in August 2008 compared to 2007. The initiation of the ice algal bloom is mainly determined by the solar angle, whereas the pelagic algal bloom requires more light and is therefore governed to a larger degree by ice thinning and the unpredictable ice breakup. We conclude that both a too early as well as a too late ice breakup can cause a mismatch between primary and secondary producers, with negative consequences for the entire lipid-based Arctic marine food web.
16920911
Global imprint of climate change on marine life
Research that combines all available studies of biological responses to regional and global climate change shows that 81–83% of all observations were consistent with the expected impacts of climate change. These findings were replicated across taxa and oceanic basins. Past meta-analyses of the response of marine organisms to climate change have examined a limited range of locations1,2, taxonomic groups2,3,4 and/or biological responses5,6. This has precluded a robust overview of the effect of climate change in the global ocean. Here, we synthesized all available studies of the consistency of marine ecological observations with expectations under climate change. This yielded a meta-database of 1,735 marine biological responses for which either regional or global climate change was considered as a driver. Included were instances of marine taxa responding as expected, in a manner inconsistent with expectations, and taxa demonstrating no response. From this database, 81–83% of all observations for distribution, phenology, community composition, abundance, demography and calcification across taxa and ocean basins were consistent with the expected impacts of climate change. Of the species responding to climate change, rates of distribution shifts were, on average, consistent with those required to track ocean surface temperature changes. Conversely, we did not find a relationship between regional shifts in spring phenology and the seasonality of temperature. Rates of observed shifts in species’ distributions and phenology are comparable to, or greater, than those for terrestrial systems.
14407133
Climate forcing multiplies biological productivity in the coastal Arctic Ocean
[1] The effects of changing ice and atmospheric conditions on the upwelling of deep nutrient-laden waters and biological productivity in the coastal Beaufort Sea were quantified using a unique combination of in situ and remote-sensing approaches. Repeated instances of ice ablation and upwelling during fall 2007 and summer 2008 multiplied the production of ice algae, phytoplankton, zooplankton and benthos by 2 to 6 fold. Strong wind forcing failed to induce upward shifts in the biological productivity of stratified waters off the shelf.