Application of a two-step approach for mapping ice thickness to various glacier types on Svalbard
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.; Braun, M. (2017). Application of a two-step approach for mapping ice thickness to various glacier types on Svalbard. Cryosphere 11(5): 2003-2032. https://dx.doi.org/10.5194/tc-11-2003-2017 In: The Cryosphere. Copernicus: Göttingen. ISSN 1994-0416; e-ISSN 1994-0424, more |   |
| Authors | | Top | - 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., more
- Lang, C., more
- Seehaus, T.
- Braun, M.
|
| 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. |
|
