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 Bølling-Allerød, 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.
Records of Neoglacial glacier activity in the Arctic constructed from moraines are often incomplete due to a preservation bias toward the most extensive advance, often the Little Ice Age. Recent warming in the Arctic has caused extensive retreat of glaciers over the past several decades, exposing preserved landscapes complete with in situ tundra plants previously entombed by ice. The radiocarbon ages of these plants define the timing of snowline depression and glacier advance across the site, in response to local summer cooling. Erosion rapidly removes most dead plants that have been recently exposed by ice retreat, but where erosive processes are unusually weak, dead plants may remain preserved on the landscape for decades. In such settings, a transect of plant radiocarbon ages can be used to construct a nearcontinuous chronology of past ice margin advance. Here we present radiocarbon dates from the first such transect on Baffin Island, which directly dates the advance of a small ice cap over the past two millennia.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.