LONG-TERM (104-105 YR) DIFFERENTIAL GLACIAL EROSION BENEATH POLYTHERMAL GLACIER ICE IN THE ATLANTIC AND ARCTIC CANADIAN HIGHLANDS

We use two terrestrial in situ cosmogenic nuclide (TCN) approaches to quantify the non-erosive character of eastern Canada highland glaciation. The first technique exploits variations in inherited TCN in 45 bedrock samples at different altitudes, and demonstrates a clear, inverse relationship between erosion rate and altitude in the Torngat Mountains, Labrador. Samples from tors on summits indicate maximum erosion rates as low as 1.6 m/Myr. Samples from streamlined bedrock protrusions a few meters above the valley floors have no inheritance (bedrock and erratic concentrations are equivalent) and consistently indicate erosion > 3 m during the last glaciation. The second approach uses the inherited TCN concentration measured in glacio-lacustrine deltaic sediment and till from north Baffin Island, Nunavut to calculate relative variations in the plateau-wide paleo-erosion rate and to qualitatively assess the duration of glacial transport and ice velocity. Deltaic sediment samples contain an inheritance equivalent to ca. 25 kyr. The erosion rates of the upland source areas at the time of delta deposition range from 8 to 15 m/Myr for maximum and minimum modeled ice cover, respectively. Based on preliminary measurements, we hypothesize that bouldery tills with monolithologic, angular clasts (“short distance tills”) that are sometimes associated with cold-based ice have relatively high TCN concentrations, whereas tills with a silty matrix and polylithologic, subrounded and striated clasts (“long distance tills”), contain little to no inherited TCN. We hope to use the distribution of till TCN inventories in concert with the University of Maine Ice Sheet Model (UMISM) with a basal temperature calculation to predict the distribution of stable, frozen-bed regions. Predicted distributions in northern Baffin grossly match zones of felsenmeer that cover the upland surfaces, as has been documented in the Torngat Mountains of Labrador.