Journal
CRYOSPHERE
Volume 11, Issue 5, Pages 2003-2032Publisher
COPERNICUS GESELLSCHAFT MBH
DOI: 10.5194/tc-11-2003-2017
Keywords
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Funding
- German Research Foundation (DFG) [FU1032/1-1]
- DFG [1158, BR2105/9-1]
- Helmholtz Association of the German Research Centres (HGF) Alliance on Remote Sensing and Earth System Dynamics
- Spanish RD projects [C11093001, C150954001]
- Polish National Centre for RD [NCBiR/PolarCLIMATE-2009/2-2/2010]
- Polish Ministry of Science and Higher Education [IPY/269/2006]
- Polish-Norwegian funding through the AWAKE project [PNRF-22-AI-1/07]
- EU FP7 ice2sea programme [226375]
- Leading National Research Centre (KNOW)
- European Research Council [320816]
- ESA [4000109873/14/I-NB]
- Norwegian Research Council [255331]
- European Research Council (ERC) [320816] Funding Source: European Research Council (ERC)
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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 landterminating glaciers as well as a 2400 km(2) 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.
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