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Spatial and Temporal Dynamics of Three East Antarctic Outlet Glaciers and Their Floating Ice Tongues

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Spatial and Temporal Dynamics of Three East Antarctic Outlet Glaciers and Their Floating Ice Tongues SPATIAL AND TEMPORAL DYNAMICS OF THREE EAST ANTARCTIC OUTLET GLACIERS AND THEIR FLOATING ICE TONGUES DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Jan Wuite, M.S. * * * * * The Ohio State University 2006 Dissertation Committee: Approved by: Dr. K.C. Jezek , Adviser Dr. C.J. van der Veen Dr. G.D. McKenzie Adviser Dr. T.J. Wilson Graduate Program in Geological Sciences ABSTRACT Recent observations show that some outlet glaciers in Greenland and Antarctica undergo rapid changes in flow velocity and ice thickness. There is concern about the implications of this for global sea levels and ocean circulation. At least part of the changes has been ascribed to changes in the dynamics of these glaciers. Measuring ice flow velocity and gradients in velocity are first steps in studying their dynamics and possible response to climatic changes. With the launch of the RADARSAT-1 satellite and the RADARSAT-1 Antarctic Mapping Project (RAMP) a great opportunity arose to derive ice flow velocity of Antarctica’s glaciers remotely. This study uses RAMP imagery to derive ice flow velocity and, in combination with various other datasets, including BEDMAP, VELMAP, OSUDEM, ICESat and InSAR derived velocity, to study spatial and temporal fluctuations in the velocity and stress fields of selected Antarctic glaciers. In particular we focus on the flow regimes of David Glacier, Mertz Glacier and Stancomb-Wills Glacier. These are all major East Antarctic outlet glaciers that have floating termini. We explore the role of these so-called ice tongues on their feeding glaciers. This is relevant especially in the wake of recent evidence that suggests the significant speed up and thinning of some glaciers in the Antarctic Peninsula is triggered by the collapse of a buttressing ice shelf. ii The derived high-resolution 2-dimensonal surface velocity maps form an important benchmark for gauging possible (future) changes in velocity and dynamics and form one of the major contributions of this study. The maps are derived using pre- established feature tracking techniques that we improved, optimized and streamlined in order to extract as much reliable velocity data as possible from the wealth of data provided by the RAMP project. This included pre-processing of the images by using a speckle reduction filter, the addition of an adaptive window extraction routine and the design and application of a noise removal filter. To determine the important flow governing forces we use pre-existing force- budget theory. We include a detailed error analysis and investigate the implications of a recently established flow law on derived stresses. The investigations of our study areas suggest that flow has been rather constant over decadal timescales. Based on this we infer that the stress field has not changed significantly either, permitting the combination of various data sets (averaged over different time spans) to optimize the velocity field in order to study dynamics in greater detail then previously possible. We find that the relative contribution of side drag declines along the fjords, but demonstrate that, once they leave the valley walls, the glaciers are not immediately true free floating ice shelves. Measurements show that ice tongues spread faster in the across flow direction than the along flow direction for a considerable length. In addition there appears to be some lateral drag, once a glacier leaves the coast, which could be associated with sub-surface valley walls or an adjacent ice shelf. This could lead to an increase in along flow creep if the ice tongue were to break off. Finally we conclude that ice tongues are important, because they can provide clues to past ice sheet behavior and fluctuations. iii Dedicated to Annemarie iv ACKNOWLEDGMENTS I have to express my gratitude to a great many people, without whom I would not have been able to complete this dissertation. First of all I would like to thank my advisor Ken Jezek for his helpful comments and suggestions throughout my studies. I enjoyed our discussions and thank you for the opportunities that you gave me. Next I have to thank my former advisor Ian Whillans, who sadly passed away in 2001. You convinced me to apply at The Ohio State University and taught me a lot about the fascinating science of glaciology. Thanks to all my committee members. Kees van der Veen, je boek is mijn bijbel geworden de laatste jaren! Lonnie Thompson, unfortunately you are in Tibet during my defense. Garry McKenzie, thanks for kindly filling the space on such short notice! Terry Wilson, I cannot express how grateful I am for the opportunity you gave me to visit Antarctica, enabling me to see my study area with my own eyes! Then, of course, I would like to show my appreciation to everyone that worked, or still works, in the remote sensing lab at Byrd Polar Research Center, including Katy, Kee-Tae, Gi-Choul, Leigh, Xiaolan, Jiahong, Tom, Bobbi, Stacy and Trey. Karl, you helped me surmount some long-standing problems I had with feature tracking. Steve, you made the lab an exiting place to be! I enjoyed our presentations for the literally hundreds v and hundreds of kids that visited our lab in recent years! Indrajit, I leave seniorship to you now. I am sure you are capable of the task! I enjoyed our science discussions and wish you good luck with the remainder of your PhD studies. I am now able to pronounce your last name fluently! Other people at BPRC that I am indebted too are Lynn E., Lynn L. and Michele, thanks for all your efforts! There is a great many other friends that I would like to thank as well. I do not know where to start, in random order: Rahul, Stefan, Yushin, Kyung In, Jason, Andy, Sarah, Brad, Kate, Mike, Jessica, Perry, Janelle, Lingke, Yuri, Sarah, Uwe, Jennifer, Raghu, Alexandra, Andrew, Amanda, Chad, Bob, Marcus, Mohammad and Roman, you all made me feel at home in Columbus, my third hometown (besides Heerlen and Amsterdam). Sandra, bedankt voor je meubels! Josh, Nick, Faezeh and Dave, I enjoyed our climbing trips at the Red River Gorge in Kentucky. You are great rope mates! Joris, Ron, Remko en Jeroen, ik heb jullie gemist! Jaap, Toos, Marleen, Tony and Pim, many thanks as well! Special thanks to my three sisters, Ingrid, Karin and Henriëtte, for their support, interest and their visits to Columbus. Also thanks to Sascha, Jelle, Ryuji, little Bart and big Niels! I am deeply indebted to my parents for their support throughout the years, you helped me a lot! Finally, Annemarie, thank you so much for your encouragement, advise and companionship! vi This work was supported by a grant from NASA’s Polar Oceans and Ice Sheets Program and by NASA Headquarters under the Earth System Science Fellowship Grant NGT5-30533. vii VITA August 24, 1974.............................................Born – Heerlen, The Netherlands 1999................................................................M.S. Physical Geography, University of Amsterdam 2000-2006 ......................................................Graduate Research Associate and Graduate Fellow, The Ohio State University FIELDS OF STUDY Major field of study: Geology viii TABLE OF CONTENTS Abstract............................................................................................................................... ii Dedication.......................................................................................................................... iv Acknowledgments............................................................................................................... v Vita...................................................................................................................................viii List of Figures................................................................................................................... xii List of Tables .................................................................................................................xviii List of Abbreviations ....................................................................................................... xix Chapter 1: Introduction....................................................................................................... 1 1.1 Introduction............................................................................................................... 1 1.2 Problem statement..................................................................................................... 3 1.3 Glacier Flow and Velocity........................................................................................ 5 1.4 Goals ......................................................................................................................... 7 1.5 Study Areas............................................................................................................... 8 1.6 Overview of the study............................................................................................. 10 Chapter 2: Theory ............................................................................................................. 13 2.1 Introduction............................................................................................................. 13 2.2 Force budget calculation......................................................................................... 14 2.2.1 Driving stress ..................................................................................................
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