Stepwise Cooling Events in the Western Arctic at 8.2 and 4.2 ka: Proxy Development and Application

Abstract

Hydroxylated glycerol dialkyl glycerol tetraether (GDGT)­based proxies have recently been proposed for reconstructing sea surface temperatures (SSTs) in polar oceans, but their reliability has not yet been sufficiently validated. We investigated the spatial distribution of hydroxylated GDGTs in surface sediments from the western Arctic Ocean and the Bering Sea to evaluate the reliability of these proxies and apply them to a sediment core from the Chukchi inner shelf to reconstruct Holocene SST variability. Among the four tested proxies, the RI­OH’ index shows the strongest correlation with annual mean SST, marking it the most reliable and well­calibrated SST proxy for this region. The RI­OH’­based SST reconstruction reveals two major cooling events at 9.1？8 ka and 4.6？3.7 ka. The earlier event coincides with intensified inflow of cold Pacific Winter Water into the Chukchi Sea, while the latter event is linked to expanded sea ice cover and advance of Alaskan glaciers, likely driven by regional shifts in atmospheric and oceanic circulation. A brief SST decline at 8.3 ka, concurrent with the well­known 8.2 ka event, is observed for the first time in the western Arctic Ocean. The latter cooling episode aligns with the 4.2 ka climate event across the Northern Hemisphere, suggesting that the Arctic climate dynamics contributed to the broader Holocene climatic transition.