COSMOGENIC NUCLIDE INSIGHTS INTO QUATERNARY LANDSCAPE EVOLUTION AND ICE SHEET HISTORY OF CENTRAL-WEST AND SOUTHWEST GREENLAND

Constraining the long-term history of the Greenland Ice Sheet (GIS) is important for improving our understanding of ice sheet dynamics and landscape evolution processes. We analyzed in situ cosmogenic ¹⁰Be and ²⁶Al in 26 rock samples from two landscapes of differing character in Uummannaq and Sukkertoppen, western Greenland. The Uummannaq landscape is a marine-terminating setting, where the margin of the GIS extends into a series of large fjords, while the Sukkertoppen landscape is a large terrestrial fringe outboard of the current land-terminating portion of the southwestern GIS margin (~200 km to east). We targeted landscapes for sampling with the potential to preserve old, relict bedrock surfaces adjacent to cold-based portions of contemporary ice caps (indicated by preservation of fragile, dead vegetation emerging from beneath presently retreating ice margins). These ice caps are currently isolated from the main GIS, but would likely have been incorporated into the ice sheet as it grew during glacial periods.

Paired isotope calculations on all samples yielded differing total histories between the two research areas. Many surfaces in the Uummannaq region have minimum exposure durations up to ca. 300 kyr, but with no significant burial (within uncertainties). Most sampled surfaces in the Sukkertoppen region, however, yield complex exposure histories with minimum cumulative exposure durations up to ca. 100 kyr and minimum cumulative burial durations up to ca. 400 kyr, yielding minimum total histories up to 500 kyr. These findings suggest that parts of the Uummannaq landscape have been essentially continuously exposed throughout much of the late Quaternary, while high-altitude surfaces in the Sukkertoppen region were largely preserved beneath non-erosive, cold-based ice during the same period. Data from the Uummannaq region thus stand in contrast to other sites surrounding Baffin Bay. We hypothesize that surfaces in this region may have remained as nunataks above Last Glacial Maximum (LGM) Greenland ice due to large amounts of ice surface drawdown in the Uummannaq Ice Stream System (UISS).