Elmer/Ice News


Investigating spatial and temporal variations in sliding of a tidewater glacier

Written by Thomas Zwinger on .


Kronebreen slidingThe variability – temporal as well as spatial - in basal friction for Kronebreen, Svalbard, a fast-flowing tidewater glacier is evaluated. This is done by inverting surface velocity data over a period of 3 years (2013–15). Due to the excellent data coverage, this is achieved at a high temporal resolution of about 11 days.  Results clearly show that sliding behaviour of Kronebreen seasonally is strongly influenced by changes in water input patterns as well as a strong inter-annual variability. Results lead to the conclusion that a physical description of the sliding of a tidewater glacier needs to exceed the complexity of a simple fixed parameter description. Basal sliding may not only be governed by local processes such as basal topography or summer melt, but also be mediated by factors that vary over a larger distance and over a longer time period such as subglacial hydrology organisation, ice-thickness changes or changes in calving front geometry.

Read more: Vallot, D., R. Pettersson, A. Luckman, D. Benn, T. Zwinger, W.J.J. van Pelt, J. Kohler, M. Schäfer, B. Claremar and N.R.J. Hulton, 2017. Basal dynamics of Kronebreen, a fast-flowing tidewater glacier in Svalbard: Non-local spatio-temporal response to water input, Journal of Glaciology, 1-13, doi:doi:10.1017/jog.2017.69.



Sensitivity of grounding line dynamics to the choice of the friction law

Written by Olivier Gagliardini on .


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.



Reconstructing glacier thickness for test geometries on Svalbard

Written by Olivier Gagliardini on .

furst2017In 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.


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