Articles | Volume 11, issue 6
The Cryosphere, 11, 2481–2490, 2017
The Cryosphere, 11, 2481–2490, 2017

Research article 03 Nov 2017

Research article | 03 Nov 2017

Analysis of ice shelf flexure and its InSAR representation in the grounding zone of the southern McMurdo Ice Shelf

Wolfgang Rack1, Matt A. King2, Oliver J. Marsh1, Christian T. Wild1, and Dana Floricioiu3 Wolfgang Rack et al.
  • 1Gateway Antarctica, University of Canterbury, Private Bag 4800, Christchurch, New Zealand
  • 2School of Land and Food, University of Tasmania, Private Bag 76, 7001 Hobart, Australia
  • 3Earth Observation Center, German Aerospace Center (DLR) Oberpfaffenhofen, 82234 Wessling, Germany

Abstract. We examine tidal flexure in the grounding zone of the McMurdo Ice Shelf, Antarctica, using a combination of TerraSAR-X repeat-pass radar interferometry, a precise digital elevation model, and GPS ground validation data. Satellite and field data were acquired in tandem between October and December 2014. Our GPS data show a horizontal modulation of up to 60 % of the vertical displacement amplitude at tidal periods within a few kilometres of the grounding line. We ascribe the observed oscillatory horizontal motion to varying bending stresses and account for it using a simple elastic beam model. The horizontal surface strain is removed from nine differential interferograms to obtain precise bending curves. They reveal a fixed (as opposed to tidally migrating) grounding-line position and eliminate the possibility of significant upstream bending at this location. The consequence of apparent vertical motion due to uncorrected horizontal strain in interferometric data is a systematic mislocation of the interferometric grounding line by up to the order of one ice thickness, or several hundred metres. While our field site was selected due to its simple boundary conditions and low background velocity, our findings are relevant to other grounding zones studied by satellite interferometry, particularly studies looking at tidally induced velocity changes or interpreting satellite-based flexure profiles.

Short summary
Predicting changes of the Antarctic Ice Sheet involves fully understanding ice dynamics at the transition between grounded and floating ice. We map tidal bending of ice by satellite using InSAR, and we use precise GPS measurements with assumptions of tidal elastic bending to better interpret the satellite signal. It allows us to better define the grounding-line position and to refine the shape of tidal flexure profiles.