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

Abstract

AbstractErosion 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.