Articles | Volume 11, issue 6
The Cryosphere, 11, 2655–2674, 2017
The Cryosphere, 11, 2655–2674, 2017

Research article 21 Nov 2017

Research article | 21 Nov 2017

GPS-derived estimates of surface mass balance and ocean-induced basal melt for Pine Island Glacier ice shelf, Antarctica

David E. Shean1,2, Knut Christianson3, Kristine M. Larson4, Stefan R. M. Ligtenberg5, Ian R. Joughin1, Ben E. Smith1, C. Max Stevens3, Mitchell Bushuk6, and David M. Holland7,8 David E. Shean et al.
  • 1Applied Physics Laboratory Polar Science Center, University of Washington, Seattle, WA, USA
  • 2Department of Civil and Environmental Engineering, University of Washington, Seattle, WA, USA
  • 3Department of Earth and Space Sciences, University of Washington, Seattle, WA, USA
  • 4Department of Aerospace Engineering Sciences, University of Colorado, Boulder, CO, USA
  • 5Institute for Marine and Atmospheric research Utrecht, Utrecht University, Utrecht, the Netherlands
  • 6Geophysical Fluid Dynamics Laboratory, Princeton University, Princeton, NJ, USA
  • 7Courant Institute of Mathematical Sciences, New York University, New York, NY, USA
  • 8Center for Global Sea-Level Change, New York University, Abu Dhabi, United Arab Emirates

Abstract. In the last 2 decades, Pine Island Glacier (PIG) experienced marked speedup, thinning, and grounding-line retreat, likely due to marine ice-sheet instability and ice-shelf basal melt. To better understand these processes, we combined 2008–2010 and 2012–2014 GPS records with dynamic firn model output to constrain local surface and basal mass balance for PIG. We used GPS interferometric reflectometry to precisely measure absolute surface elevation (zsurf) and Lagrangian surface elevation change (Dzsurf∕ Dt). Observed surface elevation relative to a firn layer tracer for the initial surface (zsurf − zsurf0′) is consistent with model estimates of surface mass balance (SMB, primarily snow accumulation). A relatively abrupt  ∼  0.2–0.3 m surface elevation decrease, likely due to surface melt and increased compaction rates, is observed during a period of warm atmospheric temperatures from December 2012 to January 2013. Observed Dzsurf∕ Dt trends (−1 to −4 m yr−1) for the PIG shelf sites are all highly linear. Corresponding basal melt rate estimates range from  ∼  10 to 40 m yr−1, in good agreement with those derived from ice-bottom acoustic ranging, phase-sensitive ice-penetrating radar, and high-resolution stereo digital elevation model (DEM) records. The GPS and DEM records document higher melt rates within and near features associated with longitudinal extension (i.e., transverse surface depressions, rifts). Basal melt rates for the 2012–2014 period show limited temporal variability despite large changes in ocean temperature recorded by moorings in Pine Island Bay. Our results demonstrate the value of long-term GPS records for ice-shelf mass balance studies, with implications for the sensitivity of ice–ocean interaction at PIG.

Short summary
We used long-term GPS data and interferometric reflectometry (GPS-IR) to measure velocity, strain rate and surface elevation for the PIG ice shelf – a site of significant mass loss in recent decades. We combined these observations with high-res DEMs and firn model output to constrain surface mass balance and basal melt rates. We document notable spatial variability in basal melt rates but limited temporal variability from 2012 to 2014 despite significant changes in sub-shelf ocean heat content.