In situ 10Be modeling and terrain analysis constrain subglacial quarrying and abrasion at Jakobshavn Isbræ, Greenland

Glacial erosion creates diagnostic landscapes and vast amounts of sediment. Yet, knowledge about the rate by which glaciers erode and sculpt bedrock and the proportion of quarried (plucked) versus abraded material is limited. To address this, we quantify subglacial erosion rates and constrain the ratio of quarrying to abrasion during the 19th/20th century overriding of a bedrock surface fronting Jakobshavn Isbræ, Greenland, by combining 10Be analyses, a digital terrain model, and field observations. Cosmogenic 10Be measurements along a 1.2-m-tall quarried bedrock step reveal a triangular wedge of quarried rock. Using individual 10Be measurements from abraded surfaces across the study area, we derive an average abrasion rate of 0.13±0.08 mm yr-1. By applying this analysis across a ~1.33 km2 study area, we estimate that the Greenland Ice Sheet quarried 378±45 m3 and abraded 322±204 m3 of material at this site. These values result in an average total erosion rate of 0.26±0.16 mm yr-1 with abrasion and quarrying contributing in roughly equal proportions within uncertainty. Additional cosmogenic 10Be analysis and surface texture mapping indicate that many lee steps are relict from the prior glaciation and were not re-quarried during the recent overriding event. These new observations of glacier erosion in a recently exposed landscape provide one of the first direct measurements of quarrying rates and indicate that quarrying accounts for roughly half of total glacial erosion in representative continental shield lithologies.