High-resolution proxy record of Holocene climate from a loess section in Southwestern Nebraska, USA
Abstract Multi-proxy analysis was used to produce a high-resolution paleoclimatic record from an exceptionally thick section of the Holocene Bignell Loess near Wauneta, Southwestern Nebraska, in the central Great Plains. The Wauneta section has excellent age control, based on optically stimulated luminescence (OSL) and radiocarbon dating, and records multiple episodes of rapid loess deposition alternating with slower deposition and soil formation. The lowermost and uppermost OSL ages obtained from the Bignell Loess are 10,250 ± 610 years (5.9 m depth) and 100 ± 10 years (0.1 m depth), respectively. As a result, the Holocene has been temporally confined. Stratigraphically, the Bignell Loess overlies the Late Pleistocene Peoria Loess (deposited ∼ 21–14 ka), and the two units are separated by the Brady Soil which is distinguished by its color and other pedogenic features. L ⁎ a ⁎ b ⁎ color parameters and organic carbon content of Bignell Loess are sensitive proxies to differentiate drought-induced aeolian sediment layers from the intercalated soil horizons. Soil organic carbon-derived δ 13 C data suggest that the C 3 -dominated floral environment during Peoria Loess deposition shifted dramatically to a C 4 -dominated environment during Brady Soil formation in response to a warming trend. Even greater C 4 abundance characterized the late Holocene. High-resolution δ 13 C data support the contention that C 3 vs. C 4 vegetation change in the Holocene reflects ecosystem response to frequent vegetation disturbance under arid conditions. Time series analysis reveals that δ 13 C and color parameters display high frequency variation with periodicities of 103–118 years and 103 years, respectively. Similar periodicities were also reported in studies of North Dakota lakes, though the physical mechanism responsible is uncertain. Comparison of Bignell Loess color and tropical Pacific sea surface temperatures (SSTs) allows evaluation of a proposed teleconnection between drought in the Great Plains and La Nina-like conditions in the tropical Pacific. The loess color index and eastern tropical Pacific SST display broad similarities through the late Pleistocene and Holocene that are consistent with this teleconnection. On the other hand, drought centered at 3800 years ago is not consistent with the teleconnection, and the end of early Holocene aridity at the Wauneta section, around 6500 years ago, is much earlier than the corresponding rise in SST and increase in El Nino frequency in the eastern tropical Pacific.