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

Discordant cosmogenic nuclide exposure ages derived from ¹⁰Be, ²⁶Al, and ¹⁴C 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 ¹⁴C records the duration of exposure during the present interglaciation; any previously acquired ¹⁴C decayed below detection limits beneath thick LIS during the last glaciation. The in situ ¹⁴C 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 ¹⁰Be and ²⁶Al 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 400 kyr suggests that the LIS was frozen to its bed across much of Baffin Island throughout the Middle and Late Quaternary.