Insights into the last deglaciation of Alaska from 10Be dating a moraine sequence deposited in the western Alaska Range

Abstract:

Mountain glacier moraines in the Arctic have not been as rigorously dated as those in lower latitudes. As such, there is uncertainty regarding which climatic factors were most important for driving mountain glacier change in the Arctic following the Last Glacial Maximum (LGM). Alaska provides an opportunity to study past mountain glacier fluctuations in the Arctic since deposits throughout the state are abundant and well-preserved. We report new cosmogenic ¹⁰Be ages from a sequence of moraines deposited in a valley in the western Alaska Range following the LGM. 24 new ¹⁰Be ages from 5 distinct moraine crests range from 18.9 – 12.3 ka (with a few likely outliers). The outermost moraine was deposited at 18.6 ± 0.4 ka, overlapping with a previously dated moraine in a neighboring valley (17.7 ± 0.5 ka). Moraines deposited approximately mid-way between the outermost dated moraine and the modern glacier terminus range between 15.9 – 14.3 ka. Additionally, an average age of 12.8 ± 0.3 ka from one moraine approximately 1 km down-valley from the modern terminus, and immediately beyond a series of late Holocene moraines, suggests that either the glacier advanced during the earliest stages of the Younger Dryas cold period (12.8 – 11.7 ka) or possibly at the culmination of the Antarctic cold reversal (14.5 – 12.8 ka). We hypothesize that while there was possibly a climatic teleconnection between the North Atlantic and Alaska – middle Younger Dryas moraines have previously been confirmed at least at one site in Alaska – it is possible that some glaciers in Alaska follow a more global, less North-Atlantic, climate pattern. Furthermore, regional climatic factors may also play an important role in late Pleistocene glacier change in Beringia.