The Cryosphere Discuss., 6, 4897-4938, 2012
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This discussion paper has been under review for the journal The Cryosphere (TC). Please refer to the corresponding final paper in TC.
Influence of ablation-related processes in the built-up of simulated Northern Hemisphere ice sheets during the last glacial cycle
S. Charbit1, C. Dumas1, M. Kageyama1, D. M. Roche1, and C. Ritz2
1IPSL/Laboratoire des sciences du climat et de l'environnement, CEA-CNRS-UVSQ UMR8212, CE Saclay, Orme des Merisiers, Bât. 701, 91191 Gif-sur-Yvette cedex, France
2UJF – Grenoble 1/CNRS, Laboratoire de glaciologie et de géophysique de l'environnement, UMR5183, Grenoble, F38041, France

Abstract. Since the original formulation of the positive-degree-day (PDD) method, different PDD calibrations have been proposed in the literature in response to the increasing number of observations. Although these formulations provide a satisfactory description of the present-day Greenland geometry, they have not all been tested for paleo ice sheets. Using the climate-ice sheet model CLIMBER-GRISLI coupled with different PDD models, we evaluate how the parameterization of the ablation may affect the evolution of Northern Hemisphere ice sheets in the transient simulations of the last glacial cycle. Results from fully coupled simulations are compared to time-slice experiments carried out at different key periods of the last glacial period. We find large differences in the simulated ice sheets according to the chosen PDD model. These differences occur as soon as the onset of glaciation, therefore affecting the subsequent evolution of the ice system. To further investigate how the PDD method controls this evolution, special attention is given to the role of each PDD parameter. We show that glacial inception is critically dependent on the representation of the impact of the temperature variability from the daily to the inter-annual time scale, whose effect is modulated by the refreezing scheme. Finally, an additional set of sensitivity experiments has been carried out to assess the relative importance of melt processes with respect to initial ice sheet configuration in the construction and the evolution of past Northern Hemisphere ice sheets. Our analysis reveals that the impacts of the initial ice sheet condition may range from quite negligible to explaining about half of the LGM ice volume depending on the representation of stochastic temperature variations which remain the main driver of the evolution of the ice system.

Citation: Charbit, S., Dumas, C., Kageyama, M., Roche, D. M., and Ritz, C.: Influence of ablation-related processes in the built-up of simulated Northern Hemisphere ice sheets during the last glacial cycle, The Cryosphere Discuss., 6, 4897-4938, doi:10.5194/tcd-6-4897-2012, 2012.
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