The Impact of Basal Roughness on Inland Thwaites Glacier Sliding

• Published in: Geophysical research letters Vol. 49; no. 14; pp. e2021GL096564 - n/a
• Main Authors: Hoffman, Andrew O., Christianson, Knut, Holschuh, Nicholas, Case, Elizabeth, Kingslake, Jonathan, Arthern, Robert
• Format: Journal Article
• Language: English
• Published: United States John Wiley & Sons, Inc 28.07.2022
• Subjects: Bed roughness; Drag; Flow; Friction; Glaciation; Glacier flow; Glacier mapping; glacier sliding; Glaciers; Hills; Ice; ice sheet modeling; Ice sheets; Modelling; Parameterization; Radar; Resolution; Roughness; Sheet modelling; Sliding; Slip; Slip resistance; Slumping; Spatial discrimination; Spatial resolution; Technology; Valleys; Wavelength; glacier sliding; ice sheet modeling; ice sheets
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2021GL096564

Swath radar technology enables three‐dimensional mapping of modern glacier beds over large areas at resolutions that are higher than those typically used in ice‐flow models. These data may enable new understanding of processes at the ice‐bed interface. Here, we use two densely surveyed swath‐mapped topographies (<50 m2 resolution) of Thwaites Glacier to investigate the sensitivity of inferred basal friction proxies to bed roughness magnitude and orientation. Our work suggests that along‐flow roughness influences inferred friction more than transverse‐flow roughness, which agrees with analytic form‐drag sliding theory. Using our model results, we calculate the slip length (the ratio of internal shear to basal slip). We find excellent agreement between the numerically derived slip lengths and slip lengths predicted by analytic form‐drag sliding theory, which suggests that unresolved short wavelength bed roughness may control sliding in the Thwaites interior. Plain Language Summary Ice‐sheet model simulations used to predict sea‐level rise require estimates of the slipperiness at the ice‐sheet base. The slipperiness is typically inferred from observations of the ice‐sheet surface; however, these inferences depend critically on how well the selected model domain resolves bumps, hills, and valleys that make up the landscape beneath the ice sheet. Over large regions, these small‐scale features are not well mapped, but new ice‐penetrating radar technology is making this more possible. Using a unique high‐resolution map of the landscape beneath a large glacier in Antarctica, we unravel how the size of bumps and hills beneath the ice affect the parameterization of the resistance field used in ice‐sheet models to simulate flow. We find that the hills, valleys, and bumps that create roughness in the landscape beneath the ice sheet influence the inferred resistance field below the spatial resolution of models and observations. We also find that bumps that block the flow of the glacier affect the inferred resistance/slipperiness of the glacier bed more than bumps that align with the flow direction. Key Points We infer high‐resolution basal resistance on Thwaites Glacier using a 3D, full‐stress model with 3D radar swath‐mapped basal topographies Drag due to material properties and flow around obstacles remain entangled below the spatial resolutions of standard models High‐wavenumber (short wavelength) basal roughness parallel to ice flow has the largest effect on the model inferred basal flow resistance