A Deglacial Ice Sheet Retreat Chronology for the Southwest Greenland Coast

Kelsey Winsor and Anders E. Carlson

9:15 am, April 27th, Room 140, Weeks Hall

During the last deglaciation, the Greenland Ice Sheet (GIS) retreated inland due to increases in insolation, surface air temperature, and ocean temperature. However, the rate and timing of this retreat is uncertain, making comparison between the forcings of ice sheet retreat and the behavior of the GIS difficult. To quantify retreat chronology, we analyze cosmogenic 10Be in boulder samples from four fjords in southwest Greenland (62°N to 67°N). Samples were collected from a range of elevations along coastal mountains, and record both initial land surface exposure as well as ice thinning rates down-slope. Preliminary data show average thinning rates of ~150-300m/kyr in all localities, with a possibility of instantaneous thinning. These rates are comparable to modern thinning rates along the GIS margin. Onset of surface exposure and full deglaciation occurred between 18 ka and ~14.5 ka in the northernmost site and at 11 to 10 ka in the three more southern locations. The observed variation in site chronologies is likely due to local factors such as fjord geometry, fjord orientation, and distance from Last Glacial Maximum ice margin. A comparison to reconstructed sea surface temperatures in the Labrador Sea shows that peak ocean warming occurred synchronous with greatest thinning rates in three of four fjords. This suggests that ocean temperatures and ice retreat were similarly forced, and is consistent with modern observations showing that warm ocean waters enhance outlet glacier thinning.

2011 UW-Madison Geoscience Graduate Symposium