Articles | Volume 11, issue 5
The Cryosphere, 11, 2003–2032, 2017
The Cryosphere, 11, 2003–2032, 2017

Research article 01 Sep 2017

Research article | 01 Sep 2017

Application of a two-step approach for mapping ice thickness to various glacier types on Svalbard

Johannes Jakob Fürst1, Fabien Gillet-Chaulet2, Toby J. Benham3, Julian A. Dowdeswell3, Mariusz Grabiec4, Francisco Navarro5, Rickard Pettersson6, Geir Moholdt7, Christopher Nuth8, Björn Sass1, Kjetil Aas8, Xavier Fettweis9, Charlotte Lang9, Thorsten Seehaus1, and Matthias Braun1 Johannes Jakob Fürst et al.
  • 1Institute of Geography, University of Erlangen-Nuremberg, Wetterkreuz 15, 91058 Erlangen, Germany
  • 2University of Grenoble Alpes, CNRS, IRD, Institut des Géosciences de l'Environnement (IGE), CS 40 700 Grenoble, France
  • 3Scott Polar Research Institute, University of Cambridge, Lensfield Road, Cambridge CB2 1ER, UK
  • 4Faculty of Earth Sciences, University of Silesia in Katowice, ul. Bankowa 12, 40-007 Katowice, Poland
  • 5Departamento de Matemática Aplicada a las Tecnologías de la Información y las Comunicaciones, desp. A302-4, ETSI de Telecomunicación, Universidad Politécnica de Madrid, Av. Complutense 30, 28040 Madrid, Spain
  • 6Department of Earth Sciences, Uppsala University, Geocentrum, Villav. 16, 752 36 Uppsala, Sweden
  • 7Norwegian Polar Institute, Fram Centre, P.O. Box 6606 Langnes, 9296 Tromsø, Norway
  • 8Department of Geosciences, University of Oslo, P.O. Box 1047, Blindern, 0316 Oslo, Norway
  • 9Department of Geography, University of Liège, Quartier Village 4, Clos mercator 3, 4000 Liège, Belgium

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.

Short summary
For the large majority of glaciers and ice caps, there is no information on the thickness of the ice cover. Any attempt to predict glacier demise under climatic warming and to estimate the future contribution to sea-level rise is limited as long as the glacier thickness is not well constrained. Here, we present a two-step mass-conservation approach for mapping ice thickness. Measurements are naturally reproduced. The reliability is readily assessible from a complementary map of error estimates.