Collaborative Research: The NE Sector of the Laurentide Ice Sheet: Dating Outlet and Local Glacier Moraines at Clyde with Cosmogenic Isotopes

Investigator: Gifford H. Miller gmiller@colorado.edu  (Principal Investigator current)          Eric J. Steig  (Co-Principal Investigator current)

Abstract

Abstract Miller OPP- 0004466

This is a collaborative proposal with the Universities of Vermont and Colorado and Bentley College. Our view of the Laurentide Ice Sheet has changed from a thick monolithic dome with a relatively stable central core to a thinner, multi-domed and more dynamic ice system with inherent instabilities.  The role of the ice sheet in the climate system includes perturbations to atmospheric flow as its height increased, and altering the planetary energy balance due to albedo changes.  In addition, through massive ice-berg and meltwater discharges, the ice sheet was a determinant on North Atlantic thermo-haline circulation. Primary information on the timing and style of continental glaciation has played a key role in this conceptual evolution.  Along the northeastern margin of the Laurentide Ice Sheet, extensive series of moraines provide a direct record of past ice-sheet behavior.  Early studies were limited by an inability to date these deposits directly.  Consequently, arguments were advanced for both a similar timing and magnitude of glacial advances along all margins of the ice sheet, and for fundamentally asynchronous responses between different sectors of the former ice sheet.  With the development of cosmogenic exposure dating, it is now possible to date the moraines directly and resolve much of this debate.  Recent studies by the Principal Investigators  have established the utility of the method by dating glacial features on southern Baffin Island and demonstrated that this region was completely glaciated at the last glacial maximum. However, they also have evidence that the northeastern coast was less intensively glaciated and preserves a much longer glacial history. The Principal Investigators will conduct a one-year study in the Clyde region which is the type site for the NE Laurentide Ice Sheet. Building on the extensive Baffin Island field experience of Miller and Davis, and the cosmogenic expertise of Bierman and Steig, they will map glacial deposits, ice-flow characteristics, and systematic changes in the glacial geomorphology, and collect samples for cosmogenic and radiocarbon dating.  Their results will establish the suitability of cosmogenic exposure dating in this region, the optimum sample type, and address the first-order question: are the extensive moraines preserved on the forelands of last glacial maximum age or do they represent much older glaciations?  The cosmogenic and radiocarbon data, linked to direct mapping of glacial deposits in the field and on aerial photographs, will allow them to better define the style and timing of glaciation, and the nature of the inception phase of a glacial cycle.