Topographical evolution and glaciation history of South Greenland constrained by paired 26Al/10Be nuclides
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The pattern of cosmogenic nuclide inheritance within bedrock surfaces in previously glaciated regions can be used to assess the efficiency of glacial erosion and constrain topographic evolution. Here, we present fifty new in-situ cosmogenic 10Be and 26Al pairs in bedrock and boulder erratics from South Greenland. The data demonstrate rapid retreat of the South Greenland Ice Sheet in the early Holocene and a clear gradient in cosmogenic nuclide inheritance in bedrock with elevation. Sites <800m above sea level (m a.s.l.) generally show limited or no nuclide inheritance (exposure from before the last glaciation). In contrast, the nuclide inheritance in samples from sites at higher elevations varies from negligible to >90kyr of exposure before the last glaciation, depending on the topographic setting. Our results suggest that steering of ice into troughs led to substantial erosion (>2.6m) in the troughs over the last glacial cycle, even at elevations above 1500 m a.s.l., while bedrock on summit flats at similar elevations experienced much less erosion. Inverse Markov-Chain Monte Carlo (MCMC) modelling of the nuclide inventories further indicates that selective linear erosion developed >1Myr ago at the summit flat closest to the present ice margin, and effectively limited the subsequent erosion to <2.6m. Erosion of the Redekammen Ridge some 40 km from the present ice margin was slightly more efficient over the last 1 Myr, indicating that selective linear erosion is less pronounced, or developed later, here than at the summit flats. Long-term ice-cover histories are generally less well-constrained than the erosion histories. The results suggest that the summit flats were possibly ice-covered during large parts of the last 1 Myr and experienced minimal erosion during this interval, but it is also possible that they were only covered by ice during the coldest parts of the glacial periods and that a cover of regolith or overlying rock was stripped off during one of the latest major glaciations. Although inverse modelling cannot distinguish between these scenarios, we identify the more likely ice-cover scenarios for each site based on the geological setting and surface characteristics.
|Journal||Earth and Planetary Science Letters|
|Publication status||Published - 15 Jul 2020|
- cosmogenic nuclides, deglaciation, glacial erosion, glaciation history, Greenland Ice Sheet, landscape evolution