Climate - cryosphere interactions for past, present and future climates with the comprehensive Earth system model AWI-ESM

Abstract

The Alfred Wegener Institute Earth System Model (AWI-ESM) is applied to study the role of the Greenland Ice Sheet (GIS) in different future warming scenarios. The model includes an interactive Ice Sheet Model (ISM) to capture ice sheet dynamics and enhance the representation of spatial freshwater discharge. The ISM leads to a strong decadal variability to the freshwater release, resulting in intervals in which it reduces the surface runoff by high accumulation rates. This compensating effect is missing in climate models without dynamic ice sheets. To investigate processes involved in the buildup phase of ice sheets, transient simulations of the Last Glacial Inception (LGI) are performed. These cooling climate simulations complement the future warming scenarios. The model is run asynchronously from 125 ka to 110 ka with prescribed orbital and greenhouse gas forcing. Large-scale glaciation occurs in a simulation with implemented anomaly coupling. This anomaly coupling is applied to compensate for model biases in high-latitude near-surface air temperature. Large areas of Quebec and Baffin Island glaciate, mainly driven by the thickening of snowfields. In order to assess the effects of heat and freshwater fluxes by iceberg melting on deep-ocean characteristics, multi-centennial simulations under fixed pre-industrial forcing are run with a fully coupled ESM including interactive icebergs. Compared to simulations without interactive icebergs, the results show a cooling of deep ocean water masses and enhanced deep water formation in the continental shelf area of the Ross Sea, a process commonly underestimated by current climate models. The results emphasize the importance of realistically representing both heat and freshwater fluxes in the high southern latitudes.