¹⁰Be measurements in bedrock constrain erosion beneath the Greenland Ice Sheet margin

Abstract

Glacial erosion is a key process driving landscape evolution, but it remains unclear what factors dictate the rate at which subglacial erosion occurs. Moreover, estimates of subglacial erosion that do not rely on sediment flux techniques are rare. Here, we present in situ 10Be measurements from bedrock surfaces in western Greenland with well‐constrained ice‐cover histories to quantify the erosion rate beneath the Greenland Ice Sheet margin during historical times. We calculate an abrasion rate of 0.72 ± 0.35 mm yr−1 and a likely total basin‐wide erosion rate (abrasion + quarrying) of ~1–1.8 mm yr−1, which are at least 1 order of magnitude higher than typical subglacial erosion rates in other polar landscapes. A compilation of published 10Be data suggests that the southwestern Greenland Ice Sheet acts as a particularly effective erosional agent within the broader Baffin Bay‐Greenland region over millennial to glacial‐interglacial timescales, suggestive of a basal ice sheet thermal regime controlled by regional climate.

Recent Advances in Our Understanding of the Role of Meltwater in the Greenland Ice Sheet System

“…However, given that meltwater volumes, ice thicknesses and rates of ice (basal) motion are typically at least an order of magnitude greater in Greenlandic as opposed to alpine glacial catchments, there seems little reason not to expect their erosion rates to at least be comparable. Furthermore, an extensive network of 32 boreholes revealed hard subglacial bed conditions [78] while airborne radar surveys observe erosional subglacial landscapes [77] that mimic the exposed proglacial landscape characterised by scoured bedrock surfaces [99]; these findings point towards the ability of the ice sheet to effectively erode the underlying bedrock, as evidenced by the bedrock erosion estimates (1-1.8 mm year −1 ) of Young et al [97].…”

“…Investigations of fjord sediment deposits in east Greenland led to the assertion that the GrIS must be characterised by very low (~0.01 mm year −1 ) erosion rates [95]. However, two recent studies from west Greenland report much higher rates of erosion:~5 mm year −1 , derived from sediment flux calculations from a large ice sheet catchment [96] and 1-1.8 mm year −1 from cosmogenic dating of exposed glaciated bedrock [97]. Cowton et al [96] argued that large volumes of meltwater accessing the glacier bed, in conjunction with fast hydraulically competent (in terms of sediment transport) drainage routing, large ice thicknesses (100-> 1000 m) and rapid motion (~100 m year −1 ) provide the ideal conditions for both generating and evacuating large volumes of subglacial sediment [98].…”

Deglaciation of coastal south‐western Spitsbergen dated with in situ cosmogenic 10Be and 14C measurements

“…In settings dominated by warm-based and erosive ice, this assumption is typically valid, but at high-latitude locations, minimally erosive polythermal and cold-based ice can result in cosmogenic nuclide datasets that are influenced by isotopic inheritance (e.g. Håkansson et al, 2008;Balco et al, 2014;Young et al, 2016). Isotopic inheritance occurs when ice is unable to erode through the $2-3 m of rock required to reset the cosmogenic clock between periods of surface exposure and the resulting nuclide concentration is an aggregate of two or more distinct periods of exposure.…”

Bedrock mega-grooves in glaciated terrain: A review

“…Fourth, numerical modelling could be used to test scenarios of groove formation and help gain insight into boundary conditions for rates of erosion. Cosmogenic nuclide dating could help constrain differential erosion between the groove base and the adjacent ridge (Briner and Swanson, 1998;Young et al, 2016). Not least, the increasing amount of data retrieved from modern subglacial environments is likely to help refine our understanding of processes at the ice -bedrock interface and thus support research into the origin of mega-grooves.…”