Elmer/Ice News

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Form of the basal friction law under PIG

Written by Olivier Gagliardini on .

PIG Fabien2016In 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 infinity 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.

More informations: Gillet-Chaulet, F., G. Durand, O. Gagliardini, C. Mosbeux, J. Mouginot, F. Rémy, and C. Ritz, 2016. Assimilation of surface velocities acquired between 1996 and 2010 to constrain the form of the basal friction law under Pine Island Glacier, Geophys. Res. Lett., 43, doi:10.1002/2016GL069937.

 

 

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Sensitivity of Barnes Ice Cap to climate state and internal dynamics

Written by Olivier Gagliardini on .

gilbert2016Barnes Ice Cap is a remnant of the Laurentide Ice Sheet, which covered much of northern North America during the Last Glacial Maximum. Barnes reached a quasi-equilibrium state ~2000 years ago and has remained similar in size since then, with a small increase during the Little Ice Age. In this study, we combine historical observations (1960–1980) with more recent satellite and airborne data (1995–2010) to drive a mass balance model coupled to a transient thermomechanical model with an adaptive mesh geometry. The model is used to characterize the current state of the ice cap and to investigate its stability as a function of climate and its own internal dynamics. On millennial time scales we show that ice flow is influenced by adjustment of an unsteady shape, by gently sloping bedrock, and by contrasting viscosities between the Pleistocene and Holocene ice. On shorter time scales, Barnes is affected by surge activity. Sensitivity tests reveal that Barnes experienced climate conditions which enabled its stability 2000 to 3000 years ago but will disappear under current climate conditions in the next millennium.

More information : Gilbert, A., G. E. Flowers, G. H. Miller, B. T. Rabus, W. Van Wychen, A. S. Gardner, and L. Copland, 2016. Sensitivity of Barnes Ice Cap, Baffin Island, Canada, to climate state and internal dynamics, J. Geophys. Res. Earth Surf., 121(8), 1516–1539, doi:10.1002/2016JF003839.

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New Beginner Elmer/Ice course this fall

Written by Olivier Gagliardini on .

We are organizing a 3-day beginner Elmer/Ice course from Monday October 31 to Wednesday November 2, 2016, at the University of Oslo (the week after the IGS Nordic Branch meeting which will be held at the Fram Centre in Tromsø, Norway, from Wednesday October 26 to Friday October 28).

This 3-days course is dedicated to students or researchers aiming to start working with Elmer/Ice. During the course, you will learn how to set up a simple ice flow problem for a flow line geometry as well as for a real mountain glacier. The third day will be dedicated to more advanced topics like the coupling of ice flow and temperature or inverse methods. For those interested, this last day might also be dedicated to start setting up your own problem with our help. 

The course is sponsored by the Department of Geosciences of the University of Oslo, the eScience tools for investigating climate change (eSTICC), CSC, LGGE and the Labex OSUG@2020.

The number of places is limited to 20, and will be given on the basis of the first registered, first served. To register, send an email to Olivier Gagliardini with you name, affiliation, position and few lines of motivations to attend the course. There will be no registration fees, but students will have to take care of their lodging and attend the course with their own laptop. More information will be given later on the Elmer/Ice website.

Elmer/Ice teachers: Adrien Gilbert, Fabien Gillet-Chaulet, Thomas Zwinger and Olivier Gagliardini
Local organising committee: Thomas V. Schuler

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