Elevation change and mass balance of Svalbard glaciers from geodetic data by Geir Moholdt PhD thesis Oslo 2010 Department of Geosciences Faculty of Mathematics and Natural Sciences University of Oslo © Geir Moholdt, 2010 Series of dissertations submitted to the Faculty of Mathematics and Natural Sciences, University of Oslo No. 1035 ISSN 1501-7710 All rights reserved. No part of this publication may be reproduced or transmitted, in any form or by any means, without permission. Cover: Inger Sandved Anfinsen. Printed in Norway: AIT Oslo AS. Produced in co-operation with Unipub. The thesis is produced by Unipub merely in connection with the thesis defence. Kindly direct all inquiries regarding the thesis to the copyright holder or the unit which grants the doctorate. Abstract The Arctic region is more affected by recent climate change than the lower latitudes. Glaciers and ice caps are sensitive indicators of climate change, and there is a high demand for more accurate quantifications of glacier changes in the Arctic. This thesis uses ground- based, airborne and spaceborne elevation measurements to estimate elevation change and mass balance of glaciers and ice caps on the Svalbard archipelago in the Norwegian Arctic. Previous assessments of the overall glacier mass balance of Svalbard have been based on in- situ measurements of surface mass balance from a limited number of sites, mainly in western Svalbard. Little has been known about the mass balance of eastern Svalbard glaciers, among those the Austfonna ice cap which covers more than 20% of the total glaciated area of 34600 km2 on Svalbard. Annual field campaigns at Austfonna were initiated in 2004, providing in- situ data on surface mass balance and elevation change which are used to validate remote sensing data. A new and more accurate DEM of Austfonna is constructed by combining satellite SAR interferometry with ICESat laser altimetry. The precision of the DEM is sufficient to correct ICESat near repeat-tracks for the cross-track topography such that multitemporal elevation profiles can be compared along each reference track. The calculated elevation changes along ICESat repeat-tracks agree well with more accurate elevation change data from airborne laser scanning and GNSS surface profiling. The average mass balance of Austfonna between 2002 and 2008 is estimated to -1.3 ± 0.5 Gt y-1, corresponding to an area- averaged water equivalent elevation change of -0.16 ± 0.06 m w.e. y-1. The entire net loss is due to a retreat of the tidewater fronts. In-situ measurements indicate a slightly positive surface mass balance of 0.05-0.12 m w.e. y-1 between 2004 and 2008. Earlier time periods are difficult to assess due limitations in the amount and quality of previous elevation data sets. Other Svalbard regions have been precisely mapped by aerial photogrammetry, so the 2003- 2008 ICESat profiles can be compared with existing topographic maps and DEMs from 1965- 1990. The mass balance for this period is estimated to -9.7 ± 0.6 Gt y-1 (or -0.36 ± 0.02 m w.e. y-1), excluding Austfonna and Kvitøya. Repeat-track ICESat data is also processed for the entire Svalbard yielding an average 2003-2008 mass balance of -4.3 ± 1.4 Gt y-1 (or -0.12 ± 0.04 m w.e. y-1) when tidewater front retreat is not accounted for. The most accurate elevation change estimates are obtained using all available ICESat data in a joint analysis where surface slope and elevation change are estimated for rectangular planes that are fitted to the data along each track. The good performance of the plane method implies that it can also be used in other Arctic regions of similar characteristics where accurate DEMs typically are not available. iii Acknowledgements This work would not have been possible without the help and inspiration from colleagues at the Section of Physical Geography, Department of Geosciences. I am especially thankful to my supervisors; Jon Ove Hagen, Andreas Kääb and Trond Eiken. Jon Ove had the idea of the project and has been of great support and encouragement throughout the years. He even gave me some salary now and then when I was running overtime! Andi has build up a good research group in remote sensing and is always knowledgeable and helpful. Trond is the “know-how” in the field and makes me feel safer at Austfonna than in downtown Oslo. He is also a great resource for all kinds of geodetic problems. The rest of the Austfonna crew, in particular Thomas V. Schuler and Thorben Dunse, is highly acknowledged for many good Austfonna discussions and invaluable help with data collection, processing and paper writing. Bernd Etzelmüller distracted me with a lot of teaching responsibility which was a very good experience after all (thanks!). Last but not least, Chris Nuth deserves a big thank you for making me expand the ICESat work to the remainder of Svalbard. Chris is always critical (in a positive way!) and it was fun to constantly dig into new problems and solve them together. I am grateful for having been given the opportunity to travel abroad for inspiring summer schools, interesting conferences (including skiing!) and a half year visit to the University of Alberta in Canada. Martin Sharp was a welcoming host, and I learned a lot from working with his group on the mighty Canadian glaciers. The research stay was possible thanks to a grant from the Leiv Eriksson mobility programme of the Research Council of Norway. Other important sources of funding relevant to my research have been the Arktisstipend grant from the Svalbard Science Forum, the ESA CryoSat Calibration and Validation Experiment (CryoVEX), the GLACIODYN project of the International Polar Year (IPY) and the ice2sea programme of the European Union 7th Framework Programme. I am also thankful to the numerous data contributors (NPI, ESA, SPIRIT-IPY, NASA/NSIDC etc.), especially the ICESat science team who basically saved my PhD project after the failure of CryoSat. It has been a pleasure to work with freely accessible data of such a high quality. Lastly, I want to thank family and friends for encouraging me to finish this work and for pulling me away from it when needed! Blindern, 20 October, 2010 Geir Moholdt v Contents ABSTRACT.............................................................................................................................iii ACKNOWLEDGEMENTS.....................................................................................................v CONTENTS............................................................................................................................vii PART I - Overview 1. INTRODUCTION ................................................................................................................ 3 1.1. MOTIVATION .................................................................................................................... 3 1.2. OBJECTIVES ...................................................................................................................... 4 1.3. OUTLINE ........................................................................................................................... 4 2. SVALBARD – CLIMATE, GLACIERS AND MASS BALANCE.................................. 6 2.1. CLIMATE CONDITIONS AND TRENDS .................................................................................. 7 2.1.1. Temperature ............................................................................................................. 7 2.1.2. Precipitation ............................................................................................................. 9 2.2. GLACIER CHARACTERISTICS ........................................................................................... 10 2.2.1. Thermal regime ...................................................................................................... 11 2.2.2. Dynamics ................................................................................................................ 12 2.3. SURFACE MASS BALANCE ............................................................................................... 14 2.3.1. Seasonal and annual field measurements .............................................................. 15 2.3.2. Ice-core analysis .................................................................................................... 17 2.3.3. Remote sensing ....................................................................................................... 18 2.3.4. Modelling ............................................................................................................... 19 2.4. CALVING ........................................................................................................................ 20 2.4.1. Ice-flux at a fixed gate ............................................................................................ 21 2.4.2. Tidewater front fluctuations ................................................................................... 21 2.5. OVERALL ESTIMATES OF MASS BALANCE........................................................................ 22 3. MEASUREMENTS OF GLACIER TOPOGRAPHY .................................................... 24 3.1. PHOTOGRAMMETRY........................................................................................................ 24 3.1.1. Topographic maps from aerial photos ................................................................... 25 3.1.2. ASTER stereo-imagery ..........................................................................................