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The Cryosphere An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/tc-2016-288
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
03 Jan 2017
Review status
This discussion paper is a preprint. A revision of this manuscript was accepted for the journal The Cryosphere (TC) and is expected to appear here in due course.
In-situ GPS records of surface mass balance and ocean-induced basal melt for Pine Island Glacier, Antarctica
David E. Shean1,2, Knut Christianson2, Kristine M. Larson3, Stefan R.M. Ligtenberg4, Ian R. Joughin1, Benjamin E. Smith1, and C. Max Stevens2 1Applied Physics Laboratory Polar Science Center, University of Washington, Seattle, WA, USA
2Department of Earth and Space Sciences, University of Washington, Seattle, WA, USA
3Department of Aerospace Engineering Sciences, University of Colorado, Boulder, CO, USA
4Institute for Marine and Atmospheric research Utrecht, Utrecht University, the Netherlands
Abstract. In the last two decades, Pine Island Glacier (PIG) experienced marked speedup, thinning, and grounding-line retreat, likely due to ice-shelf basal melt and marine ice-sheet instability. To better understand these processes, we analyzed 2008–2010 and 2012–2014 in-situ GPS records for PIG to constrain surface mass balance, firn compaction, and basal melt. We computed time series of horizontal velocity, strain rate, antenna height, surface elevation, and Lagrangian elevation change (Dh/Dt). The antenna height time series show a surface elevation increase of ~ 0.7–1.0 m/yr, which is consistent with model estimates for surface mass balance (SMB) of ~ 0.7–0.9 mwe/yr and ~ 0.7–0.8 m/yr downward velocity due to firn compaction. An abrupt ~ 0.2–0.3 m surface elevation decrease, likely due to surface melt, is observed during a period of warm atmospheric temperatures from December 2012 to January 2013. Observed Dh/Dt for all PIG shelf sites is highly linear, with trends of −1 to −4 m/yr and residuals of < 0.4 m. Corresponding basal melt rate estimates range from ~ 10 to 40 m/yr, in good agreement with those derived from ice-bottom acoustic ranging, phase-sensitive ice-penetrating radar, and high-resolution stereo DEM records. The GPS and DEM records document higher melt rates within and near features associated with longitudinal extension (transverse surface depressions, rifts). Basal melt rates for the 2012–2014 period show limited temporal variability, despite significant changes in ocean heat content, suggesting that sub-shelf melt rates may be less sensitive to ocean heat content than previously reported, at least for these locations and time periods.

Citation: Shean, D. E., Christianson, K., Larson, K. M., Ligtenberg, S. R. M., Joughin, I. R., Smith, B. E., and Stevens, C. M.: In-situ GPS records of surface mass balance and ocean-induced basal melt for Pine Island Glacier, Antarctica, The Cryosphere Discuss., https://doi.org/10.5194/tc-2016-288, in review, 2017.
David E. Shean et al.
Interactive discussionStatus: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version      Supplement - Supplement
 
RC1: 'Referee Comment', Anonymous Referee #1, 06 Mar 2017 Printer-friendly Version Supplement 
 
RC2: 'Reviewer comment', Laurence Padman, 02 May 2017 Printer-friendly Version 
 
AC1: 'Response to reviewers', David Shean, 02 Jul 2017 Printer-friendly Version Supplement 
 
AC2: 'Revised manuscript', David Shean, 02 Jul 2017 Printer-friendly Version Supplement 
 
AC3: 'Revised manuscript changes', David Shean, 02 Jul 2017 Printer-friendly Version Supplement 
David E. Shean et al.
David E. Shean et al.

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Short summary
We used long-term GPS position and antenna height time series 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 obs. with high-res DEM records and output from regional climate and firn models to constrain surface mass balance, firn compaction rates, and basal melt rates. We find that basal melt rates were nearly constant from 2012–2014, despite significant changes in sub-shelf ocean heat content.
We used long-term GPS position and antenna height time series to measure velocity, strain rate,...
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