Collaborative Research: Laurentide Ice Sheet Dynamics: Applying Cosmogenic Exposure Dating to Constrain Chronology and Glacial Style in the Eastern Canadian Arctic

University Of Colorado At Boulder, Boulder CO

Investigators

Abstract

OPP-0138586 Miller This is a collaborative proposal by Principal Investigators at the University of Colorado and Bentley College. Over the past half century, the perception of the Laurentide Ice Sheet (LIS) has developed from a thick monolithic dome with a relatively stable central core, to a thinner, multi-domed and more dynamic 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, the greatest non-linearity in the climate system. 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 LIS, 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 establish the utility of the method at Clyde and provide the basis for two competing, but testable hypotheses of the glacial history. Hypothesis 1 predicts that one of the moraine systems preserved on the Clyde and Cape Aston forelands is the last glacial maximum (LGM) marginal position, and that highlands above the moraines and coastal forelands outside the moraines remained beyond the limit of continental ice throughout the LGM. Implicit is the recognition that more extensive glaciations occurred earlier in the last glacial cycle. For hypothesis 2, preliminary results suggest that an alternative model might also be plausible: complete inundation of the region by non-erosive ice early in the LGM followed by a reorganization of the ice sheet later to a configuration similar to that projected in Hypothesis 1. Resolving these two hypotheses is probably the single most important step to understand the behavior of the LIS through the last glaciation. In addition to resolving the LGM ice limits and glacial style, the Principal Investigators will produce a detailed chronology of dated moraines from Clyde and Inugsuin fiords.