Journal cover Journal topic
The Cryosphere An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/tc-2017-30
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
17 Mar 2017
Review status
A revision of this discussion paper is under review for the journal The Cryosphere (TC).
Application of a two-step approach for mapping ice thickness to various glacier types on Svalbard
Johannes Jakob Fürst1, Fabien Gillet-Chaulet2, Toby J. Benham3, Julian A. Dowdeswell3, Mariusz Grabiec4, Francisco Navarro5, Rickard Pettersson6, Geir Moholdt7, Christopher Nuth8, Björn Sass1, Kjetil Aas8, Xavier Fettweis9, Charlotte Lang9, Thorsten Seehaus1, and Matthias Braun1 1Institute of Geography, University of Erlangen-Nuremberg, Wetterkreuz 15, 91058 Erlangen, Germany
2University of Grenoble Alpes, CNRS, IRD, Institut des Géosciences de l’Environnement (IGE), CS 40 700, Grenoble, France
3Scott Polar Research Institute, University of Cambridge, Lensfield Road, Cambridge CB2 1ER, UK
4Faculty of Earth Sciences, University of Silesia in Katowice, ul. Bankowa 12, 40-007 Katowice, Poland
5Departamento de Matemática Aplicada a las Tecnologías de la Información y las Comunicaciones, desp. A302-4, ETSI de Telecomunicación. Universidad Politécnica de Madrid, Av. Complutense 30, 28040 Madrid, Spain
6Department of Earth Sciences, Uppsala University, Geocentrum, Villav. 16, 752 36 Uppsala, Sweden
7Norwegian Polar Institute, Fram Centre, Postbox 6606 Langnes, 9296 Tromsø, Norway
8Department of Geosciences, University of Oslo, Postboks 1047, Blindern, 0316 Oslo, Norway
9Department of Geography, University of Liège, Quartier Village 4, Clos mercator 3, 4000 Liège, Belgium
Abstract. The basal topography is largely unknown beneath most glaciers and ice caps and many attempts have been made to estimate a thickness field from other more accessible information at the surface. Here, we present a two-step reconstruction approach for ice thickness that solves mass conservation over single or several connected drainage basins. The approach performs well for a variety of test geometries with abundant thickness measurements including marine- and land-terminating glaciers as well as a 2400 km2 ice cap on Svalbard. Input requirements for the first step are comparable to other approaches that have already been applied world-wide. In the first step, a geometrically controlled, non-local flux solution is converted into thickness values relying on the shallow ice approximation. In a second step, the thickness reconstruction is improved along fast-flowing glacier trunks on the basis of velocity observations. In both steps, thickness measurements are assimilated as internal boundary conditions. Each thickness field is presented together with a map of error estimates which stem from a formal propagation of input uncertainties. These estimates point out that the thickness field is least constrained near ice divides or in other stagnant areas. The error-estimate map also highlights key regions for future thickness surveys as well as a preference for across-flow acquisition. Withholding parts of the thickness measurements indicates that error estimates show a tendency to overestimate actual mismatch values. For very sparse or non-existent thickness information, our reconstruction approach indicates that we have to accept an average uncertainty of at least 25 % in the reconstructed thickness field. For Vestfonna, previous ice volume estimates have to be corrected upward by 22 %. We also find that a 12 % area fraction of the ice cap are in fact grounded below sea-level as compared to the previous 5 %-estimate.

Citation: Fürst, J. J., Gillet-Chaulet, F., Benham, T. J., Dowdeswell, J. A., Grabiec, M., Navarro, F., Pettersson, R., Moholdt, G., Nuth, C., Sass, B., Aas, K., Fettweis, X., Lang, C., Seehaus, T., and Braun, M.: Application of a two-step approach for mapping ice thickness to various glacier types on Svalbard, The Cryosphere Discuss., https://doi.org/10.5194/tc-2017-30, in review, 2017.
Johannes Jakob Fürst et al.
Johannes Jakob Fürst et al.
Johannes Jakob Fürst et al.

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Short summary
For the large majority of glaciers and ice caps, there is no information on the thickness of the ice cover. Any attempt to predict glacier demise under climatic warming and to estimate the future contribution to sea-level rise is limited as long as the glacier thickness is not well constrained. Here, we present a two-step mass-conservation approach for mapping ice thickness. Measurements are naturally reproduced. The reliability is readily assessible from a complementary map of error estimates.
For the large majority of glaciers and ice caps, there is no information on the thickness of the...
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