Combined cosmogenic 10Be, in situ 14C and 36Cl concentrations constrain Holocene history and erosion depth of Grueben glacier (CH)

Surface exposure dating with a single cosmogenic nuclide relies on the assumption of simple constant exposure. In contrast, the combination of nuclides with different half-lives or production rate depth profiles allows constraining complex exposure histories. Here we present the systematics of how the combination of Be-10, in situ C-14 and Cl-36 can be used to understand both burial and erosion in a rock surface, in addition to yielding an exposure time. Concordant ages of all three nuclides characterize simple exposure. Apparently 'too young' C-14 ages or 'too old' Cl-36 ages indicate burial or erosion of the rock surface, respectively. We further report a first data set from a proglacial granite bedrock ridge in a small cirque in the Central Swiss Alps. Three samples were exposed for 9.6 +/- 0.3 ka during the Holocene. The use of same-sample Be-10, in situ C-14 and Cl-36 allowed us to quantitatively show that these rock surfaces experienced simple constant exposure with ae<currency>500 years of ice cover and ae<currency>6 cm of erosion. In addition, the fact that samples inside and outside the Little Ice Age (LIA) ice extent yield indistinguishable ages reinforces the hypothesis that Grueben glacier reached comparable dimensions only briefly during the Holocene. Notably, at sites just inside of the LIA extent, which do exhibit fresh glacial polish, concordant ages suggest that subglacial erosion there was minimal.