Bed conditions of Pine Island Glacier, West Antarctica

• Published in: Journal of Geophysical Research: Earth Surface
• Main Authors: Brisbourne, Alex M., Smith, Andy M., Vaughan, David G., King, Edward C., Davies, D., Bingham, R.G., Smith, E.C., Nias, I.J., Rosier, Sebastian H.R.
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Geophysical Union 2017
• Subjects: West Antarctica; Pine Island Glacier; Antarc*; Antarctica; Antarctica Journal; Ice Sheet; Pine Island
• Online Access: http://nora.nerc.ac.uk/id/eprint/513935/; https://nora.nerc.ac.uk/id/eprint/513935/1/Brisbourne.pdf; http://onlinelibrary.wiley.com/wol1/doi/10.1002/2016JF004033/full

Although 90% of Antarctica's discharge occurs via its fast-flowing ice streams, our ability to project future ice sheet response has been limited by poor observational constraints on the ice-bed conditions used in numerical models to determine basal slip. We have helped address this observational deficit by acquiring and analyzing a series of seismic reflection profiles to determine basal conditions beneath the main trunk and tributaries of Pine Island Glacier (PIG), West Antarctica. Seismic profiles indicate large-scale sedimentary deposits. Combined with seismic reflection images, measured acoustic impedance values indicate relatively uniform bed conditions directly beneath the main trunk and tributaries, comprising a widespread reworked sediment layer with a dilated sediment lid of minimum thickness 1.5 ± 0.4 m. Beneath a slow-moving intertributary region, a discrete low-porosity sediment layer of 7 ± 3 m thickness is imaged. Despite considerable basal topography, seismic observations indicate that a till layer at the ice base is ubiquitous beneath PIG, which requires a highly mobile sediment body to maintain an abundant supply. These results are compatible with existing ice sheet models used to invert for basal shear stress: existing basal conditions upstream will not inhibit further rapid retreat of PIG if the high-friction region currently restraining flow, directly upstream of the grounding line, is breached. However, small changes in the pressure regime at the bed, as a result of stress reorganization following retreat, may result in a less-readily deformable bed and conditions which are less likely to maintain high ice-flow rates.