DECIPHERING ICE-SHEET EROSION IN THE EASTERN CANADIAN ARCTIC ON MILLION-YEAR TIME SCALES

The application of terrestrial cosmogenic nuclide (TCN) tools has yielded new insights into ice-sheet erosion and fiord development during the last glaciation. Owing to the generally erosive nature of ice sheets, however, few archives contain evidence of glacial erosion patterns during earlier glaciations. We compile both new and previously-published TCN and geochemical data to decipher spatial patterns of basal thermal regimes across Baffin Island on million-year time scales and present a conceptual model of fiord and landscape evolution.

Ice from the Foxe Dome of the Laurentide Ice Sheet (LIS) flowed across Baffin Island, through deep fiords in the Arctic Rim, terminating in calving margins along Baffin Bay. While highly erosive ice carved fiords and cold-based ice covered intervening highlands during the last glaciation, the broad interior plateaux were covered by a patchwork of cold- and warm-based ice. TCN concentrations in bedrock and till inland of major fiords, as well as in clasts in basal ice of the last remnant of the LIS, require >3 m of bedrock erosion during the last glaciation alone. Conversely, TCN concentrations in bedrock and till from fiord rims, interfluves between fiord onset zones, and upland surfaces suggest minimal or no erosion over the past ca. 1.5 Myr. This interpretation is supported by geomorphic features and till geochemical weathering indices.

We suggest that the evolution of basal thermal regime patterns over million-year time scales was controlled by the early Quaternary development of major fiord systems that provided highly efficient conduits for ice discharge. This focusing of flow reduced the ice flux into adjacent fiords, resulting in an increase in the area of cold-based ice present farther inland. We also suggest that some small, cold-based ice caps mantled the plateau highlands during the earliest stages of ice-sheet inception, and that this ice remained frozen to the bed for most or all of the subsequent glaciation.