Our motivation for this research has been to gain better understanding of how the Greenland Ice Sheet (GIS) responded to the very large atmospheric and ocean forcing during the last deglaciation, which involved enormous mass losses and sea-level rise, so as to assist predictions of how the GIS will respond to modern climate warming.  Using a multi-proxy approach the research successfully addressed all of its original goals, greatly improving the understanding of the past extent of the large ice streams draining into Baffin Bay from central west Greenland and also learning how the ice streams responded to the forcing of warm ocean water at its grounding line.  We learned that two central west Greenland ice streams both retreated from the shelf edge under the influence of shoaling, warm Atlantic Water that lurked initially at depths below the ice grounding lines.  We found that the deeper of the two systems retreated first, but that the ice sheet was protected from accelerating mass loss (calving) by a projecting ice shelf and by uphill bathymetry on the outer shelf.  Calving retreat was delayed until c. 15.2 cal ka BP, during another interval of ocean warming.  Another important finding is that the other ice sheet margins draining into Baffin Bay periodically released cold, fresh water that enhanced sea ice formation and slowed melting of the GIS.  This is especially apparent in the formation of a large grounding zone wedge in the Uummannaq Trough that formed when the ice margin stabilized, prior to and during the Younger Dryas cold period (12.8-11.6 cal ka BP).  At this time, the central West Greenland records document strong cooling, lack of GIS meltwater, and an increase in glacigenic sediments (ice berg rafted material) from northern Baffin Bay.  The ice sheet remained in the cross-shelf troughs until the early Holocene, when is retreated rapidly by calving and strong melting under the influence of atmosphere and ocean warming and a steep reverse slope toward the deep fjords.  One of the key cores of this study, 2008029-12PC, provided additional important information on the environment that existed in Baffin Bay during the Last Glacial Maximum (LGM).  Because we were able to obtain multiple radiocarbon dates from this core on the Disko Trough Mouth Fan, we can use multiple lines of evidence of biological activity in Baffin Bay that there was no full ice shelf formed from advance of the Hudson Strait Ice Stream that grounded on the Davis Strait and filled Baffin Bay.  That result calls into question the modeling studies that use such an ice shelf to explain the mechanics of Heinrich events. 

This project is an international effort that has drawn together researchers and students from the US, UK, Canada and Denmark. It provided materials and travel funding for two US MS students, both of whom have gone on for PhDs internationally.  Over the course of the grant it provided employment and training for 7 undergraduate students. Several of the students were women and two of the young men were veterans.  These students enjoyed working on their own projects from the beginning and also working collaboratively on a poster that they made and presented at the GSA meeting in Denver, 2013. We also used concepts and materials from this grant to provide hands-on activities for hundreds of middle school children who took our lab tour during the INSTAAR Open House.  This project has greatly advanced our understanding of the history of the GIS, especially the timing and drivers of retreat from the LGM position at the shelf edge.  The result that ocean forcing was involved in ice retreat can be used by modelers to help understand the contribution of the GIS to past sea levels and the rate at which it responded to past atmospheric warming and ocean forcing

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