A chronology of late Quaternary southwestern Greenland ice sheet retreat using terrestrial and marine records

This dissertation examines forcings of southwestern Greenland ice sheet (GrIS) retreat, and the time-scale of ice response to these drivers. Using sediment grain size analyses, planktic foraminifera Neogloboquadrina pachyderma (s) delta18O, and planktic foraminifera 14C for southeastern Davis Strait sediment core HU87033-008, early last deglaciation ice retreat is reconstructed. A peak in sediment flux 19-18 ka suggests a southwestern GrIS margin at or near the continental shelf break. Rapid retreat to the middle or inner shelf occurred by 17 ka. This timing, prior to deglacial warming in the region, points to sea level rise as the primary forcing on southwestern GrIS retreat from the outer shelf, over ~1,000 years. Following this early deglacial retreat, the southwestern GrIS maintained a shelf position until withdrawing inland of the modern coastline at 12-11 ka. Ice thinning rates at the coastline from high to low elevations, and retreat inland to the modern ice margin, are calculated using 10Be surface exposure dates from boulders along four transects. Three transects experienced strong marine influence due to extensive fjord systems, whereas the fourth transect experienced weak marine influence. Data from this dissertation demonstrates that thinning and retreat occurred quickly at the sites with marine-terminating ice between 12 and 10.5 ka, concurrent with the rise in Labrador Sea temperatures from glacial-like to interglacial-like conditions. Slow retreat rate at the land-terminating ice margin suggests that warming ocean waters were the dominant forcing on late deglacial retreat of marine-terminating outlet glaciers, which occurred over centuries to ~1,000 years. After the last deglaciation, the GrIS continued to retreat inland, then readvanced during the cooler climate of 4-0.1 ka. The maximum ice position of this late Holocene period is generally considered to be during the Little Ice Age (0.6-0.1 ka). However, 10Be surface exposure dating of boulders associated with the Narsarsuaq moraine in southern Greenland places the maximum ice extent of the Kiagtut sermiat glacier at 1.5 ka. In combination with nearby paleoclimate records, this suggests that southern Greenland may have experienced different temperature trends than that of western Greenland or northwestern Europe, driving ice response on a centennial-scale.