Assimilation of surface velocities acquired between 1996 and 2010 to constrain the form of the basal friction law under Pine Island Glacier

• Published in: Geophysical research letters Vol. 43; no. 19; pp. 10,311 - 10,321
• Main Authors: Gillet‐Chaulet, F., Durand, G., Gagliardini, O., Mosbeux, C., Mouginot, J., Rémy, F., Ritz, C.
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 16-10-2016; American Geophysical Union
• Subjects: Acceleration; Assimilation; Deformation; Drainage basins; Earth Sciences; Freshwater; Friction; Glacial basal ice; Glacier velocities; Glaciers; Glaciohydrology; ice flow modeling; Ice sheet models; inverse modeling; Islands; Mathematical models; Pine; Plastic deformation; Plastics; Sciences of the Universe; Sea level; Sediments; Slip; subglacial conditions; Surface velocity; Transient response; Pine Island; Antarctica, Ellsworth Land, Pine Island Glacier; inverse modeling; ice flow modeling; subglacial conditions
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1002/2016GL069937

In ice‐sheet models, slip conditions at the base between the ice and the bed are parameterized by a friction law. The most common relation has two poorly constrained parameters, C and m. The basal slipperiness coefficient, C, depends on local unobserved quantities and is routinely inferred using inverse methods. While model results have shown that transient responses to external forcing are highly sensitive to the stress exponent m, no consensus value has emerged, with values commonly used ranging from 1 to
∞ depending on the slip processes. By assimilation of Pine Island Glacier surface velocities from 1996 to 2010, we show that observed accelerations are best reproduced with m≥5. We conclude that basal motion, in much of the fast flowing region, is governed by plastic deformation of the underlying sediments. This implies that the glacier bed in this area cannot deliver resistive stresses higher than today, making the drainage basin potentially more sensitive to dynamical perturbations than predicted with models using standard values m = 1 or 3.
Key Points
Assimilate Pine Island Glacier surface velocities to constrain basal friction changes
Observed accelerations are consistent with a plastic deformation of subglacial sediments
The response of ice streams to perturbations could be underestimated by most ice‐sheet models