Controls on glacial erosion rates revealed by cosmogenic nuclide measurements in southeastern Alaska

Glaciers play an important role in shaping landscapes because of efficient bedrock erosion at their base. Understanding the contribution of glacial erosion to landscape evolution and the associated feedbacks between climate, erosion, and tectonics requires identifying the factors controlling glacial erosion. However, measuring glacial erosion rates is difficult due to the multifaceted combination of erosional processes occurring in glacial environments. Empirical validation of proposed controls on glacial erosion rates usually rely on indirect measurements of basin-wide sediment yields, which may include remobilized sediment and nonglacial sources of erosion that can obscure the contribution of glacial erosion. Here, we investigate glacial erosion using an alternative proxy: measurements of cosmogenic nuclides in bedrock samples (n = 28) at a glacier in southeastern Alaska. We leverage the spatial arrangement of paired in situ ¹⁴C-¹⁰Be measurements in bedrock to simultaneously determine the Holocene history of glacial cover and bedrock erosion rates. Measurements of erosion from a glacial landform suggest that quarrying rates are locally five times greater than abrasion rates. The observed spatial variability in abrasion rates (0.01 to 0.44 mm/y) supported by numerical ice-flow model results suggests that glacial erosion depends on a combination of sliding velocity and basal shear stress ("basal power"). Millennial-scale cosmogenic nuclide-derived erosion rates are an order of magnitude lower than sediment-derived erosion rates, which may suggest that sediment-derived values of bedrock erosion are overestimated due to timescale biases and/or contributions from nonglacial sources of sediment.