THE LAST DEGLACIATION OF ALASKA (Invited Presentation)

This presentation provides an overview of available glacier chronologies of the last deglaciation in Alaska. Throughout Alaska’s many centers of glaciation, moraines spanning between LGM terminal moraines and late Holocene moraines provide a detailed archive of the last deglaciation. However, few detailed moraine sequences have been dated extensively, although the number of sites with reliable chronologies is growing. The available record 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 snowline depressions being generally smaller. Some glacier re-advances and standstills during Heinrich Stadial 1 (18-15 ka) in Alaska raise the possibility of far-field effects of Atlantic meridional overturning circulation. On the other hand, some evidence for significant up-wind influence by the Laurentide Ice Sheet points to another potent forcing mechanism influencing glacier history in Alaska. The majority of glaciers scrutinized (9 out of 14 available records) were up-valley of their late Holocene glacier extents during the Younger Dryas (12.9-11.7 ka). Most of the sites with evidence for relatively extensive glaciers during the Younger Dryas are in southern Alaska, such as in the Ahklun Mountains, SW Alaska, where a well-dated moraine record points to middle-Younger Dryas glacier culmination. In addition to reviewing the above, this presentation will also include new chronologies from ongoing work in the western Alaska Range and in SE Alaska.