A major objective of ice sheet and climate research is to understand the responses of ice sheets to climate change. Ascertaining the past rates of ice-sheet retreat and contributions to sea-level rise under climate that was naturally warmer than present provides context for the future Greenland Ice-Sheet response to global warming. Here, this research team proposes to improve the deglacial chronologies and investigate retreat rates of the Laurentide (LIS) and Scandinavian (SIS) Ice Sheets during the early to mid-Holocene (<11.7 ka), a period of time that provides an excellent natural experiment where these terrestrial ice sheets deglaciated under a climate warmer than present but potentially similar to the end of this century. This project proposes to directly date the retreat of the southeastern and eastern LIS margins and the southern, eastern, and northern SIS margins during the early to mid-Holocene using in situ cosmogenic surface exposure ages, significantly improving the chronology for the largest of the LIS domes and the majority of the SIS. The resulting chronologies will be combined with already existing cosmogenic chronologies from western Quebec, northeastern Labrador and southern Finland, and existing minimum limiting radiocarbon dates and varve records. These data will allow calculations of LIS and SIS retreat rates and sea-level rise contributions during the early to mid-Holocene, with the remainder of sea-level rise largely attributable to the Antarctic Ice Sheet. The results will provide estimates of the natural rates at which ice sheets can melt under radiative forcing that may be analogous to the climate of the end of this century.
Broader Impacts Given that the greatest uncertainty in predicting future sea-level rise in response to global warming are the contributions from the remaining ice sheets, it is critical to constrain melt rates under warmer than present climates. Results of this research will provide climate scientists with estimates of the retreat rates and attendant sea-level rise contributions from terrestrial ice sheets under a climate naturally warmer than present. The information gained from this research will be of significant importance for policy decisions and of interest to a broad range of earth scientists and the public in general. This research proposal will support 2 Ph.D. students who will be exposed to a multi-disciplinary scientific approach that includes paleoclimatology, glacial geology, cosmogenic isotope geochemistry and paleoceanography. It will also provide support for an untenured, early career Assistant Professor furthering his academic career.
