Rapid and early deglaciation in the central Brooks Range, Arctic Alaska

Abstract

Alpine-style glaciation was rare in the Arctic during the last glaciation because ice sheets occupied most of the glaciated high latitudes. Due to the tight coupling of alpine-glacier fluctuations with climate, the geomorphic evidence of such fluctuations in the Brooks Range, Alaska (USA), presents a unique opportunity to study past climate changes in this portion of the Arctic. We use cosmogenic 10 Be exposure dating to directly date Last Glacial Maximum (LGM) terminal moraines and deglaciation in the central Brooks Range. 10 Be ages from moraine boulders indicate that the LGM culminated at ca. 21 ka and was followed by substantial retreat upvalley prior to a second moraine-building episode culminating at ca. 17 ka. Subsequent rapid deglaciation occurred between ca. 16 ka and 15 ka, when glaciers receded to within their Neoglacial limits. Initial deglaciation after the LGM was likely caused by ice sheet–induced atmospheric circulation changes and increasing insolation. Brooks Range glaciers largely disappeared during Heinrich Stadial 1, prior to significant warming in the North Atlantic region during the Bolling-Allerod, but coincident with global CO 2 rise. Glacier fluctuations during the late-glacial period, if any, were restricted to within their Neoglacial extents. This new chronology suggests that ice sheet–modulated atmospheric circulation and global CO 2 dominate glacial climate forcings in Arctic Alaska.