Reconstructing late Pleistocene deglaciation and Holocene glacial advance using lacustrine sediments and beryllium-10 exposure dating, Brooks Range, Arctic Alaska.

摘要

The Arctic is among the most sensitive locations to climate change, where feedback mechanisms involving the cryosphere result in climate amplification. Because of their sensitivity to summer temperature and winter precipitation, glaciers can be used as proxies for climate change and reconstructions of past glacier fluctuations provide details about paleoclimate. Here, a chronology of late Pleistocene deglaciation and Neoglacial growth is constructed for two valleys in the north-central Brooks Range, Arctic Alaska. Cosmogenic 10Be exposure dating was used on ice-sculpted valley-bottom bedrock outcrops and boulders from Holocene moraine crests. Both valleys show evidence of retreat from the range front ∼16--15 ka, and retreat into individual cirques by ∼14 ka. There is no evidence for a standstill or re-advance during Late Glacial (14--11 ka) time. Neoglaciation was underway during the middle Holocene, constrained by a moraine dated to 4.6+/-0.5 ka. Using this moraine age, and another moraine dated at 2.7+/-0.2 ka, this project confirms the accuracy of the previously established lichen growth curve to estimate moraine ages. This project also confirms that glaciers during early Neoglaciation had equal or larger extents than during the Little Ice Age (1200--1900 AD). Sediments collected from a proglacial lake downvalley of modern cirque glaciers reveal episodic sediment deposition from which it is difficult to isolate a signal of glacier advance. Comparing the lake sediment data to the moraine chronology suggests that Upper Kurupa Lake, based on the measured proxies, does not record glacial advances. Several conditions within the lake's catchment likely obscures any glacial signal. Further, more detailed measurements on the lake sediment might reveal additional clues on glacier activity. Despite the apparent lack of recording changes in glacial length, sediment characteristics suggest a period of stable deposition since 1300 AD, possibly attributed to cooling during the Little Ice Age.