The last deglaciation of Alaska

Abstract

We review available chronologies that constrain the timing of glacier fluctuations during the last deglaciation in Alaska. We address three questions relating to the last glacial termination: (i) How did the timing of glacier recession relate to buildup of global CO2, such as during the onset of CO2 rise at ~18 ka? (ii) Did glaciers fluctuate in synchrony with Heinrich Stadial 1 (18-14.6 ka)? And, (iii) what is the spatio-temporal pattern of glacier change during the climatically turbulent late glacial interval (14.6-11.7 ka)? The existing record is incomplete, yet reveals that most Alaskan glaciers experienced significant retreat (~40% of their Last Glacial Maximum lengths) prior to the onset of CO2 rise ~18 ka. This points to stronger insolation forcing of Alaskan glaciers compared to mid-latitude glaciers. Despite some glacier re-advances and standstills during Heinrich Stadial 1, most glaciers continued to recede. This suggests that glaciers in Alaska were relatively immune to the far-field effects of Atlantic meridional overturning circulation. Finally, the majority of glaciers (9 out of 14 available records) were up-valley of their late Holocene glacier extents during the Younger Dryas. Most of the sites with evidence for relatively extensive glaciers during the Younger Dryas are in southern Alaska, which may relate to moisture changes associated with the flooding of Bering Strait as much as it does to changes in North Atlantic Ocean circulation.