LATE PLEISTOCENE GLACIAL HISTORIES FROM THE NW AND NE CORNERS OF NORTH AMERICA

We have recently investigated the late Pleistocene glacial history of the northeastern Laurentide Ice Sheet (LIS) on Baffin Island and of various alpine glaciers across the state of Alaska. Cosmogenic exposure dating, supplemented with radiocarbon dating, has constrained the timing of advance and retreat of glaciers during marine isotope stage (MIS) 2. In the northeast corner of North America, the LIS outlet glacier that filled Clyde Fiord expanded sometime after ~34 ka to its terminal position on the continental shelf of Baffin Bay, it retreated from its terminal position ~13 ka, fluctuated in the outer fiord until 10 ka, retreated rapidly to the fiord head by 9 ka, and finally receded from the fiord head ~8 ka. In the northwest corner of North America, we have constrained the timing of deglaciation from terminal MIS 2 moraines in six regions across the state of Alaska; the advance phase is constrained at three of these sites. Alpine glaciers generally began to advance between 30 and 25 ka, reaching terminal positions between ~27 and ~21 ka. Glaciers retreated from their local MIS 2 maxima: ~22 ka in the Ahklun Mountains (SW Alaska); ~16-18 ka in the Chuilnuk Mountains (SW Alaska); ~20 ka in the western Alaska Range (central Alaska); ~24-27 ka in the Kokrines Hills (west-interior Alaska); ~21-23 ka in the Yukon Tanana Upland (east-interior Alaska); and ~24-26 ka in the northeastern Brooks Range (NE Alaska). Overall, glacier retreat in Alaska was concurrent with the peak of the last global glacial maximum, probably in response to limited moisture availability. On the other hand, the retreat of the northeastern LIS occurred late during global deglaciation, possibly because this sector of the LIS was sustained for some time by local increases in precipitation during climate amelioration. The records from these areas stress the importance of local factors in influencing the details of glacier histories.