Date of Award

Spring 1-1-2010

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Atmospheric & Oceanic Sciences

First Advisor

Anne E. Jennings

Second Advisor

John Cassano

Third Advisor

Weiqing Han

Abstract

The Greenland Ice Sheet (GIS) is currently thinning and retreating. One of the focal points for present research on the GIS retreat is Jakobshavn Isbrae, the largest ice stream on Greenland’s West coast, which is retreating today at least in part from ocean subsurface warming (Holland et al., 2008). Jakobshavn is located in Disko Bay, which receives warm Atlantic water from the West Greenland Current (WGC). In this thesis we present multi-proxy data from four marine sediment cores that help constrain the timing of ice retreat from the continental shelf and identify the marine conditions that accompanied retreat. Cores were taken in a transect from the outer shelf to near the mouth of the isfjord and basal dates give minimum ages of retreat from the shelf, bay sill, and near shore of 11.4, 11.1, and 9.4 cal kyr BP.

Foraminiferal assemblages and IRD counts from these cores indicate that after rapid retreat of the GIS the region experience cold conditions. Atlantic waters, via the WGC were first felt in the bay sometime between 9 and 8.5 cal. kyr BP. A possible strengthening of the WGC is seen on the shelf at approximately 7.0 cal. kyr BP. A dramatic rise in calcareous fauna from 6.2 – 3.5 cal. kyr BP in all cores indicates a significant shift in the strength of the WGC, with warm, Atlantic associated fauna gradually increasing and peaking at 4.5 cal. kyr BP. This coincides with the believed retreat of Jakobshavn Isbrae behind its present margin (Weidick et al.,1990), suggesting that subsurface warming may have played a part in the ice stream’s retreat in the past. The region returns to colder conditions by 3.0 cal. kyr BP, indicating a late onset of neoglacial cooling.

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