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The Cryosphere An interactive open-access journal of the European Geosciences Union
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Volume 12, issue 6
The Cryosphere, 12, 1969-1985, 2018
https://doi.org/10.5194/tc-12-1969-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.
The Cryosphere, 12, 1969-1985, 2018
https://doi.org/10.5194/tc-12-1969-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 12 Jun 2018

Research article | 12 Jun 2018

Antarctic sub-shelf melt rates via PICO

Ronja Reese1,3, Torsten Albrecht1, Matthias Mengel1, Xylar Asay-Davis1,2, and Ricarda Winkelmann1,3 Ronja Reese et al.
  • 1Potsdam Institute for Climate Impact Research (PIK), Member of the Leibniz Association, P.O. Box 60 12 03, 14412 Potsdam, Germany
  • 2Los Alamos National Laboratory, P.O. Box 1663, T-3, MS-B216, Los Alamos, NM 87545, USA
  • 3University of Potsdam, Institute of Physics and Astronomy, Karl-Liebknecht-Str. 24-25, 14476 Potsdam, Germany

Abstract. Ocean-induced melting below ice shelves is one of the dominant drivers for mass loss from the Antarctic Ice Sheet at present. An appropriate representation of sub-shelf melt rates is therefore essential for model simulations of marine-based ice sheet evolution. Continental-scale ice sheet models often rely on simple melt-parameterizations, in particular for long-term simulations, when fully coupled ice–ocean interaction becomes computationally too expensive. Such parameterizations can account for the influence of the local depth of the ice-shelf draft or its slope on melting. However, they do not capture the effect of ocean circulation underneath the ice shelf. Here we present the Potsdam Ice-shelf Cavity mOdel (PICO), which simulates the vertical overturning circulation in ice-shelf cavities and thus enables the computation of sub-shelf melt rates consistent with this circulation. PICO is based on an ocean box model that coarsely resolves ice shelf cavities and uses a boundary layer melt formulation. We implement it as a module of the Parallel Ice Sheet Model (PISM) and evaluate its performance under present-day conditions of the Southern Ocean. We identify a set of parameters that yield two-dimensional melt rate fields that qualitatively reproduce the typical pattern of comparably high melting near the grounding line and lower melting or refreezing towards the calving front. PICO captures the wide range of melt rates observed for Antarctic ice shelves, with an average of about 0.1m a−1 for cold sub-shelf cavities, for example, underneath Ross or Ronne ice shelves, to 16m a−1 for warm cavities such as in the Amundsen Sea region. This makes PICO a computationally feasible and more physical alternative to melt parameterizations purely based on ice draft geometry.

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Floating ice shelves surround most of Antarctica and ocean-driven melting at their bases is a major reason for its current sea-level contribution. We developed a simple model based on a box model approach that captures the vertical ocean circulation generally present in ice-shelf cavities and allows simulating melt rates in accordance with physical processes beneath the ice. We test the model for all Antarctic ice shelves and find that melt rates and melt patterns agree well with observations.
Floating ice shelves surround most of Antarctica and ocean-driven melting at their bases is a...
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