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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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Simultaneous inversion of basal friction and bed elevation

Written by Olivier Gagliardini on .

mosbeux gmd2016Ice flow models are now routinely used to forecast the ice sheets’ contribution to 21st century sea-level rise. For such short term simulations, the model response is greatly affected by the initial conditions. Data assimilation algorithms have been developed to invert for the friction of the ice on its bedrock using observed surface velocities. A drawback of these methods is that remaining uncertainties, especially in the bedrock elevation, lead to non-physical ice flux divergence anomalies resulting in undesirable transient effects. In this study, we compare two different assimilation algorithms based on adjoints and nudging to constrain both bedrock friction and elevation. Using synthetic twin experiments with realistic observation errors, we show that the two algorithms lead to similar performances in reconstructing both variables and allow the flux divergence anomalies to be significantly reduced.

More informations: Mosbeux, C., F. Gillet-Chaulet and O. Gagliardini, 2016. Comparison of adjoint and nudging methods to initialise ice sheet model basal conditions, Geosci. Model Dev., 9, 2549-2562, doi:10.5194/gmd-9-2549-2016.

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