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

• Published in: Journal of geophysical research. Earth surface Vol. 126; no. 12
• Main Authors: Balter‐Kennedy, A., Young, N. E., Briner, J. P., Graham, B. L., Schaefer, J. M.
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 01-12-2021
• Subjects: Bedrock; Beryllium 10; Climate; Climate change; Climate sensitivity; Depth; Earth; Earth surface; Erosion rates; Glacial erosion; Glaciation; Glacier flow; Glaciers; Greenland ice sheet; Ice ages; Ice sheets; Landscape; landscape evolution; Pleistocene; Subglacial erosion; Topography; Valleys; Greenland
• ISSN: 2169-9003; 2169-9011
• DOI: 10.1029/2021JF006429

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.
Plain Language Summary
Glaciers and ice sheets are among the most powerful erosional forces on Earth, with the ability to alter topography and cut deep valleys into the landscape on relatively short timescales. The total amount of erosion and the pace at which it takes place affects how the glaciers flow and how they respond to climate changes. The pace of erosion beneath glaciers, however, is difficult to measure because it takes place in an environment that is difficult to access. Here, we use specialized chemical measurements that tell us how long the bedrock has been exposed at the Earth's surface when the landscape was ice‐free. These measurements also allow us to learn about the pace of erosion beneath the Greenland Ice Sheet (GrIS) over the last 2.7 million years when the Earth experienced repeated ice ages. We find that the pace of erosion beneath the GrIS has remained relatively consistent over the Pleistocene, a finding that helps us understand how the topography of Greenland has evolved through time.
Key Points
10Be measurements indicate that centennial‐scale erosion rates near Jakobshavn Isbræ were 0.3–0.8 mm yr−1
Orbital‐scale erosion rates derived from a 10Be depth profile in a bedrock core were 0.1–0.3 mm yr−1
Erosion rates beneath the Greenland Ice Sheet near Jakobshavn Isbræ remained relatively constant through the Pleistocene