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.
Institute of Geography, University of Erlangen-Nuremberg, Wetterkreuz 15, Erlangen, Germany; University of Grenoble Alpes, CNRS, IRD, Institut des Géosciences de l'Environnement (IGE), Grenoble, CS 40-700, France; Scott Polar Research Institute, University of Cambridge, Lensfield Road, Cambridge, United Kingdom; Faculty of Earth Sciences, University of Silesia in Katowice, ul. Bankowa 12, Katowice, Poland; Departamento de Matematica Aplicada A Las Tecnologias de la Informacion y Las Comunicaciones, ETSI de Telecomunicación, Universidad Politécnica de Madrid, Av. Complutense 30, Madrid, Spain; Department of Earth Sciences, Uppsala University, Geocentrum, Villav. 16, Uppsala, Sweden; Norwegian Polar Institute, Fram Centre, P.O. Box 6606 Langnes, Tromsø, Norway; Department of Geosciences, University of Oslo, P.O. Box 1047, Blindern, Oslo, Norway; Department of Geography, University of Liège, Quartier Village 4, Clos mercator 3, Liège, Belgium
Recommended Citation:
Jakob Fürst J,, Gillet-Chaulet F,, Benham T,et al. Application of a two-step approach for mapping ice thickness to various glacier types on Svalbard[J]. Cryosphere,2017-01-01,11(5)