Glacial-Geological/Geomorphological Research in West Greenland Used to Test an Ice-Sheet Model

Ice sheet modeling is an essential tool for estimating the effect of climate change on the Greenland ice sheet. The large spatial and long-term temporal scale of ice sheet models limits the amount of data which can be used to test model results. A framework for the analysis of glacial geological data to test ice sheet models is illustrated by a case study in west Greenland. A geological scenario of ice margin positions since the last glacial maximum is based on a review of existing literature and new datings of moraine systems. Ages of moraine systems and associated accuracy ranges are interpolated to a 1 × 1 km grid over an area of about 57,500 km2. Resampling to a 20 × 20 km grid on an ice sheet model coordinates permits a quantitative comparison with modeled ice marginal positions. In view of the uncertainties in the geological scenario, with moraine system ages having an absolute uncertainty of 700 to 3300 cal yr, the Greenland ice sheet model of Huybrechts provides a reasonable simulation of the deglaciation pattern in central west Greenland. Modeled timing of the position of the ice margin generally precedes the geological record by 900 yr. The difference between geology and model is large for areas without proper geological information and small, but still about 500-950 yr, for well-dated moraine systems. Model deficiencies in west Greenland are probably related to the forcing function driving ablation estimates, and especially the forcing function for sea level and the description of calving processes should he reviewed critically. The simplified topography used by the model could also induce errors. Although topography used in models neglects possible important features such as ice streams, we do not find any significant trend between differences and relief amplitude. Missing moraines on the southern part of the shelf and absence of geological information from beneath the present ice sheet affect the character and quality of the geological scenario.