Holocene glacier fluctuations in south-central Alaska reflect hydroclimate changes in a region strongly influenced by large-scale features of North Pacific climate. Glacier fluctuations over the past approximately 2300 years were inferred from multiple geophysical and geochemical properties of a new 13-m-long sediment core from proglacial Skilak Lake. The chronology is based on annual-layer (varve) counting, supported by radiocarbon ages and the identification of the 1912 CE Katmai tephra. Sediment density and accumulation rate show two prominent century-scale increases, one near the base of the cored sequence (around 270-370 BCE) and one near the top (around 1600–1900 CE, Little Ice Age). These two peaks, and the absence of such increases between them, coincide with sedimentation-rate changes as previously measured in multiple cores from Eklutna Lake, located 130 km northeast of Skilak Lake. The similarity between the two sedimentary sequences, despite their contrasting geomorphic settings and spatial scales, implies that regional climate change is the overriding control. Sediment with high bulk density and thick varves was deposited concurrently with the expansion of glaciers in the catchment and elsewhere in the region during the Little Ice Age. We likewise attribute the deposits with similar characteristics to expanded glaciers centered around 320 BCE, and the absence of such sediment during the intervening 1800 years to the lack of a major glacier advance. Climatologically, both periods of high sediment accumulation rate correspond with times of intensified Aleutian Low pressure, as recently reconstructed based on regional syntheses of oxygen-isotope records for the earlier period, and on sea-salt concentration in two Alaskan ice cores for the later period. Both periods also coincide with pronounced multi-decadal downturns in combined solar and volcanic global radiative forcing. The massive buildup of glaciers during the Little Ice Age might reflect the increased frequency of these downturns combined with millennial-scale decrease in orbitally driven insolation. Glaciolacustrine records from these two lakes add a new perspective on the multi-century variability of glaciers and hydroclimate in the North Pacific region.
Bibliographical noteFunding Information:
This project was funded by National Science Foundation award 1602106 to DSK and by Research Foundation- Flanders ( FWO ) grant G042812N to MDB.
This project was funded by National Science Foundation award 1602106 to DSK and by Research Foundation-Flanders (FWO) grant G042812N to MDB.We appreciate the helpful suggestions from Greg Wiles and two anonymous viewers, and the invaluable assistance in the field from Koen De Rycker, Thomas Mestdagh, Adrian Bender, and Peter Haeussler. Varves of core SK-2 were counted by: Anouk Verwimp, C?cile-Marie Lissens, Elke Ghyselbrecht, Flore Van Maldeghem, Frie Van Bauwel, Goedroen Lamote, Hendrik Plas, Jasper Withoeck, Joke De Paepe, Lotte Hermans, Marlies Wermersche, Maxim Steurbaut, Robbe Pauwels, Sarah Williamson, Sien Thys, Stijn Albers, Elke Vandekerkhove, Inka Meyer, Katleen Wils, Jasper Moernaut and co-authors NP and MVD. Katleen Wils and Evelien Boes helped sample the organic material for 14C analysis. We thank Rik Achten for the use of the medical CT scanner at the Ghent University Hospital, and the U.S. Geological Survey and U.S. Fish and Wildlife Service for their support of this project.
© 2021 Elsevier Ltd
- Glaciolacustrine sediment
- North Pacific region
- Sediment accumulation rate
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