THE HUNT FOR THE LAST GLACIAL MAXIMUM, NORTHEASTERN BAFFIN ISLAND: NEW COSMOGENIC EXPOSURE AGE CONSTRAINTS ON THE EXTENT OF THE LAURENTIDE ICE SHEET

A preliminary set of 24 cosmogenic exposure ages combined with new glacial mapping in the Clyde Inlet region (70°N, 70°W) provides a new understanding of the last glacial maximum (LGM) on northeastern Baffin Island. The extent and timing of Laurentide Ice Sheet advances throughout the eastern Canadian Arctic at the LGM have been poorly known largely due to a lack of LGM-age radiocarbon ages for glacial deposits. Recent approaches using lacustrine sediment cores and cosmogenic exposure dating have resulted in significant advances toward understanding Laurentide ice dynamics across southeastern Baffin Island (64° to 67°N, 62° to 68°W; Steig et al., 1998; Bierman et al., 1999; Miller et al., 1999; Marsella et al., 2000; Wolfe et al., 2000; Kaplan et al., 2001). However, unlike in southern Baffin Island where LGM ice left a limited moraine record, the wide coastal forelands of the Clyde region afford the opportunity to study a far more extensive LGM and pre-LGM moraine record.

Our ¹⁰Be and ²⁶Al ages range from 19 ka for a terminal moraine on the Clyde foreland, to 13 ka and 9 ka for morphostratigraphically younger foreland and fiord-wall lateral moraines and ice-sculpted bedrock islands within Clyde Inlet. This LGM ice limit is intermediate between earlier depictions of the LGM margin at the fiord head (>100 km inland; Miller and Dyke, 1974), and at the continental shelf break in Baffin Bay (80 km beyond; Hughes et al., 1977), and thus resolves a long-standing controversy. ¹⁰Be ages from a higher fiord-wall lateral moraine of 32 ka, along with yet undated terminal moraines on the coastal foreland beyond the 19 ka terminal moraine, indicate that the Laurentide was more extensive during pre-LGM times than during the LGM. We infer that there was relatively extensive ice at high latitudes early in the last glacial cycle, during relatively wet times, versus more restricted ice during the arid LGM (e.g., Miller et al., 1977; Miller et al., 1992); ongoing research will further test this hypothesis.