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Title: Application of a two-step approach for mapping ice thickness to various glacier types on Svalbard
Authors: Furst, Johannes Jakob
Gillet-Chaulet, Fabien
Benham, Toby J.
Dowdeswell, Julian A.
Grabiec, Mariusz
Navarro, Francisco
Pettersson, Rickard
Moholdt, Geir
Nuth, Christopher
Sass, Bjorn
Aas, Kjetil
Fettweis, Xavier
Lang, Charlotte
Seehaus, Thorsten
Braun, Matthias
Keywords: Ice thickness; Mapping method
Issue Date: 2017
Citation: Cryosphere, Vol. 11, iss. 5 (2017), s. 2003-2032
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 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.
DOI: 10.5194/tc-11-2003-2017
ISSN: 1994-0416
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