Climate and relief-induced controls on the temporal variability of denudation rates in a granitic upland.

How soil erosion rates evolved over the last about 100 ka and how they relate to environmental and climate variability is largely unknown. This is due to a lack of suitable archives that help to trace this evolution. We determined in situ cosmogenic beryllium-10 (Be-10) along vertical landforms (tors, boulders and scarps) on the Sila Massif to unravel their local exhumation patterns to develop a surface denudation model over millennia. Due to the physical resistance of tors, their rate of exhumation may be used to derive surface and, thus, soil denudation rates over time. We derived soil denudation rates that varied in the range 0-0.40 mm yr(-1). The investigated boulders, however, appear to have experienced repositioning processes about 20-25 ka bp and were therefore a less reliable archive. The scarps of the Sila upland showed a rapid bedrock exposure within the last 8-15 ka. Overall, the denudation rates increased steadily after 75 ka bp but remained low until about 17 ka bp. The exhumation rates indicate a denudation pulse that occurred about 17-5 ka bp. Since then the rates have continuously decreased. We identify three key factors for these developments - climate, topography and vegetation. Between 75 and 17 ka bp, climate was colder and drier than today. The rapid changes towards warmer and humid conditions at the Pleistocene-Holocene transition apparently increased denudation rates. A denser vegetation cover with time counteracted denudation. Topography also determined the extent of denudation rates in the upland regime. On slopes, denudation rates were generally higher than on planar surfaces. By determining the exhumation rates of tors and scarps, soil erosion rates could be determined over long timescales and be related to topography and particularly to climate. This is key for understanding geomorphic dynamics under current environmental settings and future climate change.