Centennial- and Orbital-Scale Erosion Beneath the Greenland Ice Sheet Near Jakobshavn Isbræ

Erosion beneath glaciers and ice sheets is a fundamental Earth-surface process dictating landscape development, which in turn influences ice-flow dynamics and the climate sensitivity of ice masses. The rate at which subglacial erosion takes place, however, is notoriously difficult to observe because it occurs beneath modern glaciers in a largely inaccessible environment. Here, we present (a) cosmogenic-nuclide measurements from bedrock surfaces with well constrained exposure and burial histories in front of Jakobshavn Isbræ in western Greenland to quantify centennial-scale erosion rates since ∼1850 CE, and (b) a new method combining cosmogenic-nuclide measurements in a shallow bedrock core with cosmogenic-nuclide modeling to determine orbital-scale erosion rates across the same landscape. Twenty-seven ¹⁰Be measurements in surficial bedrock constrain the erosion rate during historical times to 0.4–0.8 mm yr⁻¹. Seventeen ¹⁰Be measurements in a 4-m-long bedrock core yield a centennial-scale erosion rate of 0.3–0.6 mm yr⁻¹, corroborating the results from our surface samples, and reveal that ¹⁰Be concentrations below ∼2 m depth are greater than what is predicted by an idealized production-rate depth profile. We utilize this excess ¹⁰Be at depth to constrain orbital-scale erosion rates at Jakobshavn Isbræ to 0.1–0.3 mm yr⁻¹. The broad similarity between centennial- and orbital-scale erosion rates suggests that subglacial erosion rates have remained relatively uniform throughout the Pleistocene adjacent to Jakobshavn Isbræ.