Modelling present glacier dynamics on Svalbard - from inferring surface velocities to computing a flow-consistent bedrock map
Geodesy, Photogrammetry, Remote Sensing, Geoinformatics, Cartography
Final Report Abstract
The primary goal of this project was the reconstruction of ice-thickness maps for all 1668 glaciers on the Svalbard archipelago. For this purpose, an approach for mapping glacier ice thickness was implemented in the existing Elmer/Ice modelling framework. The initial plan was to pursue a 2D mass conserving inverse method that requires contemporaneous 2D information on surface mass balance, surface velocities and elevation changes as well as on the glacier geometry. This initial approach did participate in the first phase of the Ice Thickness Model Intercomparison Experiments (ITMIX), an activity of the International Association of Cryospheric Sciences (IACS). The approach convinced in the synthetic experiments for which the input field were perfectly consistent. Yet it was not ready for realworld application. The main obstacle was the insufficient quality and poor coverage of remotely sensed velocity information in areas of little glacier movement. On these grounds, it was decided to develop a two-step reconstruction approach that does not require velocity observations and guarantees glacier-wide applicability in its first step. A scaling relation between ice-flux and thickness that stems from a common ice-dynamic approximation was applied to cut this dependence. In the second step, thickness values are refined in sub-domains where velocity measurements are reliable. In both steps thickness measurements are readily assimilated. The performance of this two-step approach was then presented for well-surveyed ice caps as well as marine- and land-terminating glaciers on Svalbard. By gradually withholding more thickness measurements, the reliability of the reconstructed thickness maps was scrutinised with regard to measurement availability. The thickness product is complemented by an error estimate map that builds on stringent propagation of input uncertainties along the glacier flow. For the application of the approach to the whole of Svalbard, a regional map of glacier surface velocities for 2015/2016 was inferred from Sentinel-1 imagery by offset tracking. Moreover, an exceptional thickness record of more than one million point measurements was acquired from 18 international partners, compiled for utilisation and, in mutual agreement, submitted to the glacier thickness database (GlaThiDa3.01) of the World Glacier Monitoring Service. Finally, the reconstruction approach was automatized for regional applicability. Alongside the publication, the first Svalbard icefree topography (SVIFT1.0) map was made publically available via the Norwegian Polar Data Centre. This map showed unprecedented quality. Instead of the initial goal to prepare ice-dynamic forward simulations on Svalbard by inverting for the unknown basal conditions, priority was given to keep up with two activities of the IACS working group on glacier ice thickness estimation. The first activity was the participation in the second phase of ITMIX. The goal of ITMIX2 was to identify well-performing reconstruction approaches in the case that thickness measurements are available. Results have been submitted and a joint publication is planned. The second, more demanding activity was the global glacier thickness initiative (G2TI). The general aim was to provide a multi-model estimate of the thickness distribution of all glaciers worldwide. Only five approaches did participate. Results were meanwhile presented in Nature Geoscience and consensus thickness maps for all glaciers on Earth were made publically available. For the successful participation, further workflow automation and optimisation for high-performance computing was accomplished. Within G2TI, the novel reconstruction approach did produce thickness maps for more than 100’000 of the 215’000 glaciers worldwide. For Svalbard, the SVIFT map produced in this project replaced all other model results because of the abundant measurement record that has been compiled and assimilated but was not available to all participants. The newly developed reconstruction was the only approach that did reproduce available thickness measurements and that did not simplify the geometry complexity of the problem at some point. Yet for the majority of unsurveyed glaciers, no improved performance was found. Considering statistical properties of the G2TI model ensemble, the methodological independence with respect to the four other participant approaches, which show some degree of relation amongst each other, made the 2D mass-conserving approach a key contribution to the global consensus estimate.
Publications
- (2016) The safety band of Antarctic ice shelves, Nature Climate Change, 6, 479-482
J.J. Fürst, G. Durand, F. Gillet-Chaulet, L. Tavard, M. Rankl, M.H. Braun, O. Gagliardini
(See online at https://doi.org/10.1038/NCLIMATE2912) - (2017) Application of a two-step approach for mapping ice thickness to various glacier types on Svalbard, The Cryosphere, 11, 2003-2032
J.J. Fürst, F. Gillet-Chaulet, T.J. Benham, J.A. Dowdeswell, M. Grabiec, F. Navarro, R. Pettersson, G. Moholdt, C. Nuth, B. Sass, K. Aas, X. Fettweis, C. Lang, T. Seehaus and M.H. Braun
(See online at https://doi.org/10.5194/tc-11-2003-2017) - (2017) Dynamic changes on the Wilkins Ice Shelf during the 2006-2009 retreat derived from satellite observations, The Cryosphere , 11, 1199-1211
M. Rankl, J.J. Fürst , A. Humbert and M.H. Braun
(See online at https://doi.org/10.5194/tc-11-1199-2017) - (2017) How accurate are estimates of glacier ice thickness? Results from ITMIX, the Ice Thickness Models Intercomparison eXperiment, The Cryosphere, 11, 949-970
D. Farinotti, D.J. Brinkerhoff, G.K.C. Clarke, J.J. Fürst, H. Frey, P. Gantayat, F. Gillet-Chaulet, C. Girard, M. Huss, P.W. Leclercq, A. Linsbauer, H. Machguth, C. Martin, F. Maussion, M. Morlighem, C. Mosbeux, A. Pandit, A. Portmann, A. Rabatel, RAAJ Ramsankaran, T.J. Reerink, O. Sanchez, P.A. Stentoft, S. Singh Kumari, W.J.J. van Pelt, B. Anderson, T.J. Benham, D. Binder, J.A. Dowdeswell, A. Fischer, K. Helfricht, S. Kutuzov, I. Lavrentiev, R. McNabb, G.H. Gudmundsson, H. Li and L.M. Andreassen
(See online at https://doi.org/10.5194/tc-11-949-2017) - (2018) The ice-free topography of Svalbard, Geophysical Research Letters, 45, 11760-11769
J.J. Fürst, F. Navarro, F. Gillet-Chaulet, M. Huss, G. Moholdt, X. Fettweis, C. Lang, T. Seehaus, S. Ai, T.J. Benham, D.I. Benn, H. Björnsson, J.A. Dowdeswell, M. Grabiec, J. Kohler, I. Lavrentiev, K. Lindbäck, K. Melvold, R. Pettersson, D. Rippin, A. Saintenoy, P. Sánchez-Gámez, T.V. Schuler, H. Sevestre, E. Vasilenko and M.H. Braun
(See online at https://doi.org/10.1029/2018GL079734) - (2019) A consensus estimate for the ice thickness distribution of all glaciers on Earth, Nature Geoscience , 12, 168-173
D. Farinotti, M. Huss, J.J. Fürst , J. Landmann, H. Machguth, F. Maussion, Ankur Pandit
(See online at https://doi.org/10.1038/s41561-019-0300-3) - (2019) Enthalpy budget evolution during the surge of a polythermal glacier: a test of theory, Journal of Glaciology, 1-15
D.I. Benn, R.L. Jones, A. Luckmann, J.J. Fürst, I. Hewitt and C. Sommer
(See online at https://doi.org/10.1017/jog.2019.63)
