Changes in volume and geometry of the Austre Dahlfonna glacier (Spitsbergen island) in 2008–2019

Previously published geodetic mass balance data indicate glacier shrinkage in the Barentsburg area of Svalbard since the beginning of the 20th century on the decadal time scale. However, observations for shorter time spans allowing one to compute the inter-annual variability of the mass balance are scarce. The study presents results of ground-based GNSS and the GPR surveys of the Austre Dahlfonna glacier (2 sq km) located on Spitsbergen island, south of the town of Barentsburg. According to the GPR survey of spring 2019 at 50 MHz frequency, the area-averaged ice thickness was equal to 82 m, while the maximum was 170 m. The results confirm the polythermal structure of the glacier, with a layer of underlying temperate ice. Since the end of the Little Ice Age, the area of Austre Dahlfonna has halved. By comparing the GNSS survey results (the end of the melt season of 2019) with the co-registered archived remote sensing data (ArcticDEM strip of 2013 and S0 Terrengmodell of 2008), it was computed that, within the last 12 years (2008–2019), Austre Dahlfonna lost 16 % of its volume, which corresponds to a geodetic mass balance of –12.05 ± 0.85 m w. e. The mass loss in 2008–2013 (5.22 ± 0.37 m w. e.) was lower than in 2013–2019 (6.83 ± 0.48 m w. e.), which is in agreement with the ongoing direct measurements on the neighboring Austre Grønfjordbreen glacier and with the archipelago-wide mass-balance patterns. We demonstrate that the less intensive glacier mass loss, which occurred in 2005–2012 and was detected previously for the whole archipelago, definitely took place in the Barentsburg area as well. This time interval is characterized by the prevalence of a negative NAO phase (65 % of recurrence), which may indicate more frequent intrusions of colder Arctic air masses. This fact proves that the mass-balance variability of the Barentsburg area glaciers is governed in time spans of 5–10 years by regional-scale factors, presumably by shifts in the atmospheric circulation regimes.