Dating of raised marine and lacustrine deposits in east Greenland using beryllium-10 depth profiles and implications for estimates of subglacial erosion

摘要

Here we combine ~(10)Be depth profile techniques applied to late glacial ice-contact marine and lacustrine deltas, as well as boulder exposure dating of associated features in the Scoresby Sound region, east Greenland, to determine both the surface age and the magnitude of cosmogenic nuclide inheritance. Boulder ages from an ice-contact delta in northern Scoresby Sund show scatter typical of polar regions and yield an average age of 12.8±0.5ka - about 2ka older than both our average profile surface age of 10.9±0.7ka from three depth profiles and a radiocarbon-based estimate. On the other hand, boulder exposure ages from a set of moraines in southern Scoresby Sund show excellent internal consistency for polar regions and yield an average age of 11.6±0.2ka. The profile surface age from a corresponding ice-contact delta is 8.1±0.9ka, while a second delta yields an age of 10.0±0.4ka. Measured ~(10)Be inheritance concentrations from all depth profiles are internally consistent and are between 10% and 20% of the surface concentrations, suggesting a regional cosmogenic inheritance signal for the Scoresby Sound landscape. Based on the profile inheritance concentrations, we explore the first-order catchment-averaged bedrock erosion under the Greenland ice sheet, yielding estimates of total erosion during the last glacial cycle of the order of 2-30m.