COSMOGENIC NUCLIDES AND PALEOGLACIOLOGY IN THE EASTERN CANADIAN ARCTIC

Cosmogenic nuclide measurements provide quantitative data on the form of past ice sheets and processes at their beds, information that was previously often difficult or impossible to acquire. Exposure data have helped to define firmly the location and timing of former ice streams or outlet glaciers, which in past studies were based often on quasi-quantitative information. The techniques have played a key role in constructing a new paradigm for the glacial history of passive continental margins around the North Atlantic Ocean, especially for Arctic Canada, during the last glacial period. Although only a small part of the ice sheet in terms of areal extent, low gradient ice provides a mechanism for highly dynamic ice sheets, despite frigid ice-age Arctic conditions, that interacted with the adjacent sea including during Heinrich Events. Exposure data have also helped to improve our understanding of former bed conditions, including basal thermal regime and the amount of glacial erosion. As an example, in the Cumberland Sound region, southern Baffin Island, ¹⁰Be and ²⁶Al ages show major changes in glacial erosion rate associated with both cold and warm-based ice. A simple analysis of 13 ¹⁰Be measurements, even from areas that show strong evidence of recent glacial scouring, indicates 10³-10⁴ isotope concentrations that cannot be explained with a Holocene exposure duration and reflect inheritance from exposure prior to the last glaciation. Assuming ~constant exposure during the last interglacial, followed by ~100,000 yrs of ice coverage, the diverse concentrations observed in the samples can be explained with ~25cm to >2 meters of glacial erosion (2.5 to >20 mm/ka) during the last glaciation.