Basal slip accounts for a large part of the flow of ice streams draining ice from Antarctica and Greenland into the ocean. Therefore, an appropriate representation of basal slip in ice flow models is a prerequisite for accurate sea level rise projections. Various friction laws have been proposed to describe basal slip in models. Here, we compare the influence on grounding line (GL) dynamics of four friction laws: the traditional Weertman law and three effective pressure-dependent laws, namely the Schoof, Tsai and Budd laws. It turns out that, even when they are tuned to a common initial reference state, the Weertman, Budd and Schoof laws lead to thoroughly different steady-state positions, although the Schoof and Tsai laws lead to much the same result. In particular, under certain circumstances, it is possible to obtain a steady GL located on a reverse slope area using the Weertman law. Furthermore, the predicted transient evolution of the GL as well as the projected contributions to sea level rise over a 100-year time horizon vary significantly depending on the friction law. We conclude on the importance of choosing an appropriate law for reliable sea level rise projections and emphasise the need for a coupling between ice flow models and physically based subglacial hydrological models.
Read more: Brondex, J., O. Gagliardini, F. Gillet-Chaulet and G. Durand, 2017. Sensitivity of grounding line dynamics to the choice of the friction law, Journal of Glaciology, 63(241), 854-866, doi:10.1017/jog.2017.51.
In this study, we present a two-step reconstruction approach for mapping glacier thickness that solves mass conservation over single or several connected drainage basins. The approach is applied to a variety of test geometries with abundant thickness measurements including marine- and land-terminating glaciers as well as an ice cap on Svalbard. In the first step, a geometrically controlled, non-local flux solution is converted into thickness values relying on the shallow ice approximation (SIA). In a second step, the thickness field is updated along fast-flowing glacier trunks on the basis of velocity observations. Both steps account for available thickness measurements. Each thickness field is presented together with an error-estimate map based on a formal propagation of input uncertainties. For Vestfonna ice cap, a previous ice volume estimate based on the same measurement record as used here has to be corrected upward by 22 %. We also find that a 13% area-fraction of the ice cap is in fact grounded below sea level. The former 5%-estimate from a direct measurement interpolation exceeds the aggregate error range of 6–23%.
Read more: Fürst, J. J., F. Gillet-Chaulet, T. J. Benham, J. A. Dowdeswell, M. Grabiec, F. Navarro, R. Pettersson, G. Moholdt, G., C. Nuth, B. Sass, K. Aas, X. Fettweis, C. Lang, T. Seehaus and M. Braun, 2017. Application of a two-step approach for mapping ice thickness to various glacier types on Svalbard, The Cryosphere, 11, 2003-2032, doi:10.5194/tc-11-2003-2017.
We are organizing two Elmer/Ice courses this fall:
- A 2-day beginner Elmer/Ice course will take place the 23rd and 24th of October 2017 at the University of Stockholm (Sweden, local organising committee: Nina Kirchner), just before the Nordic Branch IGS meeting held in Uppsala. This 2-day course is dedicated to students or researchers aiming to start working with Elmer/Ice. It is sponsored by the University of Stockholm, CSC, IGE, eSTICC and the Labex OSUG@2020.
- A 3-day advanced Elmer/Ice workshop will take place the 22nd, 23rd and 24th of November 2017 at IGE (Grenoble, France). This 3-day course is dedicated to students or researchers having already an experience using Elmer/Ice. It is sponsored by IGE, CSC and the Labex OSUG@2020.
For both courses, the number of places is limited to 20, and will be given on the basis of first registered, first served.To register, send an email to Olivier Gagliardini with your name, affiliation, position and few lines of motivations to attend the course. Don't forget to specify which course you want to register to. There will be no registration fees, but students will have to take care of their own travel and lodging and attend the course with their own laptop (preferentially with Elmer/Ice installed). More information will be given later on the Elmer/Ice website.