The last deglaciation of Alaska and a new benchmark 10Be moraine chronology from the western Alaska Range

We report 50 new and 22 previously published Be-10 ages from 15 distinct moraine crests in the western Alaska Range spanning from the Last Glacial Maximum (LGM) terminal moraine to a latest Pleistocene moraine immediately down valley from late Holocene moraines. Moraines were deposited between 21.3 +/- 0.8 ka and 12.8 +/- 0.6 ka and conform morphostratigraphically, giving us high confidence in the chronology. Our record, and the key records reviewed in our compilation from across Alaska indicate a culmination of the regional LGM between ca. 21-19 ka. Our chronology, unmatched in resolution from a single valley in Alaska, indicates that steady glacier recession from ca. 21-18 ka was punctuated by accelerated retreat from ca. 17-16 ka, followed by a period of prolonged moraine deposition between ca. 16 and 15 ka. After ca. 15 ka rapid glacier retreat was punctuated by a re-advance ca. 12.8 ka. Other chronologies across Alaska show further evidence of moraine deposition between ca. 16-15 ka and ca. 13-12 ka. The emerging pattern of glacier retreat through the last deglaciation in Alaska is compared to several global, regional, and local climate proxies to assess what climate factors controlled the timing and pace of glacier retreat in Alaska. We hypothesize that warming caused by rising boreal summer insolation drove initial and steady deglaciation from the LGM terminal moraine position until ca. 18 ka, after which time global warming from rising CO2 concentrations accelerated retreat. Subsequent periods of moraine deposition in Alaska coincide with decreasing trends in the NGRIP ice core record, at the culmination of Heinrich Stadial 1 (ca. 16-15 ka), and during the early Younger Dryas between 13 and 12.5 ka. While comparisons are made between alpine glacier records and the timing of other geologic events that may have impacted local-to-regional climate (e.g., the opening of the Bering Strait, the saddle collapse between the Laurentide and Cordilleran Ice sheets, and post-LGM Bering Sea dynamics), the relationship between our record and these geologic events are ambiguous. We suggest glaciers across Alaska were possibly more sensitive to other regional and global climate forcing mechanisms, mainly rising insolation, global CO2 rise, and Northern Hemisphere Ocean circulation forcing through deglaciation. (C) 2022 Elsevier Ltd. All rights reserved.

Automated summary

The study reports the chronology of moraine crests in the western Alaska Range, indicating the culmination of the regional Last Glacial Maximum around 21-19 ka. The retreat of glaciers in Alaska experienced periods of steady recession and accelerated retreat, influenced by various climate factors. The findings suggest that glacier retreat in Alaska was sensitive to factors such as warming, global warming, and ocean circulation.