Quantifying Sub-Glacial Abrasion at Jakobshavn Isbræ: A Novel Approach Using In Situ 10Be Measurements

Abstract:

Warm-based ice sheets and glaciers incontrovertibly erode and modify the terrain that they

mantle; yet precise estimates of the rate and magnitude of sub-glacial erosion are rare.

Estimates of sub-glacial erosion occurring beneath ice sheets, such as the Greenland Ice

Sheet, are particularly important because they can provide key insights into sediment

availability at ice-sheet margins that influences ice-sheet stability. Furthermore, estimates

of sub-glacial erosion can help inform predictive geophysical ice-sheet models that

incorporate a basal sliding parameter. Here, we take advantage of a detailed ice-margin

history at Jakobshavn Isbræ over the last ~7,500 years, combined with in situ 10Be

measurements from strategic bedrock locations, to quantify the rate of sub-glacial abrasion

beneath Jakobshavn Isbræ’s land-based margins. Our bedrock samples are from 1)

locations that deglaciated ~7,500 years ago and have remained ice-free through present

day, and 2) locations that also deglaciated ~7,500 years ago, but were re-occupied by the

ice-margin during the last few hundred years. After accounting for the slightly different

exposure histories between bedrock locations, and despite the short duration in ice-cover,

initial 10Be measurements reveal a detectable difference in 10Be concentrations between the

two bedrock surfaces. We hypothesize that the offset in 10Be concentrations reveals the

magnitude of sub-glacial abrasion beneath Jakobshavn Isbræ’s land-terminating margins.