Millennial scale variability of denudation rates for the last 15 kyr inferred from the detrital 10 Be record of Lake Stappitz in the Hohe Tauern massif,Austrian Alps

Abstract

Reconstructing paleo-denudation rates over Holocene timescales in an Alpine catchment provides a unique opportunity to isolate the climatic forcing of denudation from other tectonic or anthropogenic effects. Cosmogenic ¹⁰Be on two sediment cores from Lake Stappitz (Austrian Alps) were measured yielding a 15-kyr-long catchment-averaged denudation record of the upstream Seebach Valley. The persistence of a lake at the outlet of the valley fixed the baselevel, and the high mean elevation minimizes anthropogenic impacts. The ¹⁰Be record indicates a decrease in the proportion of paraglacial sediments from 15 to 7 kyr cal. BP after which the ¹⁰Be concentrations are considered to reflect hillslope erosion and thus can be converted to denudation rates. These ones significantly fluctuated over this time period: lower hillslope erosion rates of ca. 0.4 mm/year dated between 5 and 7 kyr cal. BP correlate with a stable climate, sparse flooding events and elevated temperatures that favoured the widespread growth of stabilizing soils and vegetation. Higher hillslope erosion rates of ca. 0.8 mm/year over the last ~4 kyr correlate with a variable, cooler climate where frequent flooding events enhance denudation of less protected hillslopes. Overall, our results suggest a tight coupling of climate and hillslope erosion in alpine landscapes as it has been observed in other parts of the Alps.