Limited ice-sheet erosion and complex in situ cosmogenic 10Be, 26Al, and 14C on Baffin Island, Arctic Canada

Discordant cosmogenic nuclide exposure ages derived from Be-10, Al-26, and C-14 extracted from quartz in rocky summits along the eastern rim of the central Baffin Island plateau provide constraints on the efficiency of erosion by the Laurentide Ice Sheet (LIS) and on the timing and duration of ice-free conditions in the eastern Canadian Arctic. In situ C-14 records the duration of exposure during the present interglaciation; any previously acquired C-14 decayed below detection limits beneath thick LIS during the last glaciation. The in situ C-14 exposure ages for two samples adjacent to a cold-based local ice cap are significantly less than for a nearby ice-free summit, suggesting that an expanded local ice cap shielded the ice-adjacent sites for at least 800 years, longer than the duration of the Little Ice Age. Disequilibrium between Be-10 and Al-26 concentrations in the same samples can be realistically explained by brief (ca. 10 kyr) intervals of exposure during peak interglacials (MIS 11, 9, 7, 5e, and 1), separated by long (ca. 50-100 kyr) intervals of complete shielding by the LIS. The lack of glacial erosion for at least the past 400kyr suggests that the LIS was frozen to its bed across much of Baffin Island throughout the Middle and Late Quaternary. (C) 2006 Elsevier Ltd. All rights reserved.