Abstract
Abstract. In this paper, we propose a new sub-grid scale parameterization for the ice discharge into the ocean through outlet glaciers and inspect the role of different observational and palaeo constraints for the choice of an optimal set of model parameters. This parameterization was introduced into the polythermal ice-sheet model SICOPOLIS, which is coupled to the regional climate model of intermediate complexity REMBO. Using the coupled model, we performed large ensemble simulations over the last two glacial cycles by varying two major parameters: a melt parameter in the surface melt scheme of REMBO and a discharge scaling parameter in our parameterization of ice discharge. Our empirical constraints are the present-day Greenland ice sheet surface elevation, the surface mass balance partition (ratio between total ice discharge and total precipitation) and the Eemian interglacial elevation drop relative to present day in the vicinity of the NEEM ice core. We show that the ice discharge parameterization enables us to simulate both the correct ice-sheet shape and mass balance partition at the same time without explicitly resolving the Greenland outlet glaciers. For model verification, we compare the simulated total and sectoral ice discharge with other estimates. For the model versions that are consistent with the range of observational and palaeo constraints, our simulated Greenland ice sheet contribution to Eemian sea-level rise relative to present-day amounts to 1.4 m on average (in the range of 0.6 and 2.5 m).
Highlights
Since standard coarse-resolution Greenland ice sheet (GrIS) ice sheet models cannot simulate a realistic present-day surface orography of the GrIS and at the same time have the correct mass balance partition, we developed a novel approach, which allows us to circumvent this problem without resolving individual ice streams and outlet glaciers – and without an increase in computational cost
We introduced a new sub-grid scale ice discharge parameterization aimed at mimicking Greenland’s fast outlet glaciers in a coarse resolution ice-sheet model
The ice discharge parameterization enables us to simulate an ice sheet, whose shape is in good agreement with observations and whose partition between total ice discharge and total surface melt is in good agreement with stateof-the-art regional climate models
Summary
Modelling the response of the Greenland ice sheet (GrIS) to anthropogenic warming has already been undertaken for more than 2 decades (Huybrechts et al, 1991; van de Wal and Oerlemans, 1997; Huybrechts and de Wolde, 1999; Greve, 2000) and attracted considerable attention in recent years (Vizcaíno et al, 2010; Goelzer et al, 2011; Graversen et al, 2011; Applegate et al, 2012; Lipscomb et al, 2013; Stone et al, 2013), including higher-order and full Stokes modelling approaches (Price et al, 2011; Seddik et al, 2012; Goelzer et al, 2013). Since standard coarse-resolution GrIS ice sheet models cannot simulate a realistic present-day surface orography of the GrIS and at the same time have the correct mass balance partition, we developed a novel approach, which allows us to circumvent this problem without resolving individual ice streams and outlet glaciers – and without an increase in computational cost. This approach is in the spirit of our previous modelling work (Robinson et al, 2010, 2011, 2012) and is based on a rather simple semi-empirical parameterization of ice discharge through the outlet glaciers.
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