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Application of a two-step approach for mapping ice thickness to various glacier types on Svalbard
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 is applied to 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. The input requirements are kept to a minimum for the first step. In this 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. These error estimates point out that the thickness field is least constrained near ice divides or in other stagnant areas. Withholding a share of the thickness measurements, error estimates tend to overestimate mismatch values in a median sense. We also have to accept an aggregate uncertainty of at least 25 % in the reconstructed thickness field for glaciers with very sparse or no observations. For Vestfonna ice cap (VIC), 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 an aggregate maximum range of 6–23 % as inferred from the error estimates here.
- Norwegian Polar Institute Norway
- Faculty of Earth Sciences Poland
- Université de Liège (ULiège) Belgium
- University of Liège Belgium
- University of Oslo Norway
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Aas, K., Dunse, T., Collier, E., Schuler, T., Berntsen, T., Kohler, J., and Luks, B.: The climatic mass balance of Svalbard glaciers: a 10-year simulation with a coupled atmosphereglacier mass balance model, The Cryosphere, 10, 1089-1104, https://doi.org/10.5194/tc-10-1089-2016, 2016. [OpenAIRE]
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Bishop, M., Olsenholler, J., Shroder, J., Barry, R., Raup, B., Bush, A., Copland, L., Dwyer, J., Fountain, A., Haeberli, W., Kääb, A., Paul, F., Hall, D., Kargel, J., Molnia, B., Trabant, D., and Wessels, R.: Global Land Ice Measurements from Space (GLIMS): Remote Sensing and GIS Investigations of the Earth's Cryosphere, Geocarto Int., 19, 57-84, https://doi.org/10.1080/10106040408542307, 2004.
Błaszczyk, M., Jania, J., and Hagen, J.: Tidewater glaciers of Svalbard: Recent changes and estimates of calving fluxes, Polish Polar Res., 30, 85-142, 2009. [OpenAIRE]
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Braun, M., Pohjola, V., Pettersson, R., Möller, M., Finkelnburg, R., Falk, U., Scherer, D., and Schneider, C.: Changes of glacier frontal positions of Vestfonna (Nordaustlandet, Svalbard), Geograf. Ann. A, , 93, 301-310, https://doi.org/10.1111/j.1468- 0459.2011.00437.x, 2011.
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Brinkerhoff, D. J., Aschwanden, A., and Truffer, M.: Bayesian Inference of Subglacial Topography Using Mass Conservation, Front. Earth Sci., 4, 1-15, https://doi.org/10.3389/feart.2016.00008, 2016.
- Norwegian Polar Institute Norway
- Faculty of Earth Sciences Poland
- Université de Liège (ULiège) Belgium
- University of Liège Belgium
- University of Oslo Norway
- Department of Geosciences University of Oslo Norway
- Universidad Politécnica de Madrid Spain
- Fram Centre Norway
- Friedrich-Alexander University Erlangen-Nürnberg Germany
- University of Silesia Poland
- UNIWERSYTET SLASKI W KATOWICACH Poland
- University of Cambridge United Kingdom
- UNIVERSITETET I OSLO Norway
- University of Erlangen-Nuremberg Germany
- Norwegian Film Institute Norway
- Grenoble Alpes University France
- French National Centre for Scientific Research France
- Friedrich-Alexander-Universität Erlangen-Nürnberg Germany
- University of Silesia in Katowice Poland
- Uppsala University Sweden
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 is applied to 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. The input requirements are kept to a minimum for the first step. In this 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. These error estimates point out that the thickness field is least constrained near ice divides or in other stagnant areas. Withholding a share of the thickness measurements, error estimates tend to overestimate mismatch values in a median sense. We also have to accept an aggregate uncertainty of at least 25 % in the reconstructed thickness field for glaciers with very sparse or no observations. For Vestfonna ice cap (VIC), 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 an aggregate maximum range of 6–23 % as inferred from the error estimates here.