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Discussion papers
https://doi.org/10.5194/tc-2019-70
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/tc-2019-70
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 16 May 2019

Research article | 16 May 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal The Cryosphere (TC).

Glacial cycles simulation of the Antarctic Ice Sheet with PISM – Part 2: Parameter ensemble analysis

Torsten Albrecht1, Ricarda Winkelmann1,2, and Anders Levermann1,2,3 Torsten Albrecht et al.
  • 1Potsdam Institute for Climate Impact Research (PIK), Member of the Leibniz Association, Potsdam, Germany
  • 2Institute of Physics and Astronomy, University of Potsdam, Potsdam, Germany
  • 3Lamont-Doherty Earth Observatory, Columbia University, New York, USA

Abstract. The Parallel Ice Sheet Model (PISM) is applied to the Antarctic Ice Sheet over the last two glacial cycles (≈ 210,000 years) with a resolution of 16 km. A Large Ensemble of 256 model runs is analyzed in which four relevant model parameters have been systematically varied using full-factorial parameter sampling. Parameters and plausible parameter ranges have been identified in a companion paper (Albrecht et al., 2019) and are associated with ice dynamics, climatic forcing, basal sliding and bed deformation and represent distinct classes of model uncertainties. The model is calibrated against both modern and geologic data, including reconstructed grounding line locations, elevation-age data, ice thickness and surface velocities as well as uplift rates. An aggregated score is computed for each ensemble member that measures the overall model-data misfit, including measurement uncertainty in terms of a Gaussian error model (Briggs and Tarasov, 2013). The statistical method used to analyze the ensemble simulation results follows closely the simple averaging method described in Pollard et al. (2016).

This analysis further constrains relevant model and boundary parameters by revealing clusters of best fit parameter combinations. The ensemble of reconstructed histories of Antarctic Ice Sheet volumes provides a score-weighted likely range of sea-level contributions since the Last Glacial Maximum of 9.4 ± 4.1 m (or 6.5 ± 2.0 × 106 km3), which is at the upper range of previous studies. The last deglaciation occurs in all ensemble simulations after around 12,000 years before present, and hence after the Meltwater Pulse-1A. Our Large Ensemble analysis also provides well-defined parametric uncertainty bounds and a probabilistic range of present-day states that can be used for PISM projections of future sea-level contributions from the Antarctic Ice Sheet.

Torsten Albrecht et al.
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Short summary
A large ensemble of glacial cycle simulations of the Antarctic Ice Sheet with PISM has been analyzed, in which four relevant model parameters have been systematically varied. These parameters have been selected in a companion study and are associated with uncertainties in both ice dynamics, climatic forcing, basal sliding and solid Earth deformation. For each ensemble member a statistical score is computed, which enables to calibrated the model against both modern and geologic data.
A large ensemble of glacial cycle simulations of the Antarctic Ice Sheet with PISM has been...
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