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https://doi.org/10.5194/tc-2019-277
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/tc-2019-277
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 16 Dec 2019

Submitted as: research article | 16 Dec 2019

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A revised version of this preprint is currently under review for the journal TC.

A protocol for calculating basal melt rates in the ISMIP6 Antarctic ice sheet projections

Nicolas C. Jourdain1, Xylar Asay-Davis2, Tore Hattermann3,4, Fiammetta Straneo5, Helene Seroussi6, Christopher M. Little7, and Sophie Nowicki8 Nicolas C. Jourdain et al.
  • 1Univ. Grenoble Alpes/CNRS/IRD/G-INP, IGE, Grenoble, France
  • 2Los Alamos National Latoratory, Los Alamos, NM, USA
  • 3Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany
  • 4Norwegian Polar Institute, Tromsø, Norway
  • 5Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, USA
  • 6Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
  • 7Atmospheric and Environmental Research, Inc., Lexington, Massachusetts, USA
  • 8NASA GSFC, Cryospheric Sciences Branch, Greenbelt, USA

Abstract. Climate model projections have previously been used to compute ice-shelf basal melt rates in ice-sheet models, but the strategies employed – e.g. ocean input, parameterization, calibration technique, and corrections – have varied widely and are often ad-hoc. Here, a methodology is proposed for the calculation of circum-Antarctic basal melt rates for floating ice, based on climate models, that is suitable for ISMIP6, the Ice Sheet Model Intercomparison Project for CMIP6 (6th Coupled Model Intercomparison Project). The past and future evolution of ocean temperature and salinity is derived from a climate model by estimating anomalies with respect to the modern day, which are added to an present-day climatology constructed from existing observational datasets. Temperature and salinity are extrapolated to any position potentially occupied by a simulated ice shelf. A simple formulation is proposed for a basal-melt parameterization in ISMIP6, constrained by the observed temperature climatology, with a quadratic dependency on either the non-local or local thermal forcing. Two calibration methods are proposed: 1) based on the mean Antarctic melt rate (MeanAnt) and 2) based on melt rates near Pine Island's deep grounding line (PIGL). Future Antarctic mean melt rates are an order of magnitude greater in PIGL than in MeanAnt. The PIGL calibration, and the local parameterization, result in more realistic melt rates near grounding lines. PIGL is also more consistent with observations of interannual melt rate variability underneath Pine Island and Dotson ice shelves. This work stresses the need for more physics and less calibration in the parameterizations, and for more observations of hydrographic properties and melt rates at interannual and decadal time scales.

Nicolas C. Jourdain et al.

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Nicolas C. Jourdain et al.

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Short summary
To predict the future contribution of the Antarctic contribution to sea level rise, we need to use ice sheet models. The lce Sheet Model Intercomparison Project for AR6 (ISMIP6) builds an ensemble of ice-sheet projections constrained by atmosphere and ocean projections from the 6th Coupled Model Intercomparison Project (CMIP6). In this work, we present a method to derive ice-shelf basal melting in ISMIP6 from the CMIP6 ocean outputs, and we give examples of projected melt rates.
To predict the future contribution of the Antarctic contribution to sea level rise, we need to...
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