A comprehensive Earth System Model (AWI-ESM) with interactive ice sheets and icebergs: A step towards realistic freshwater fluxes for abrupt climate change scenarios

Icebergs play a crucial role in Earth's climate system. They transport large amounts of fresh water and alter ocean salinity, affect sea-ice formation, and can lead to abrupt climate changes in the past. Hence, a proper representation of icebergs in Earth system models (ESMs) is essential to improve the understanding of processes involved in abrupt climate changes. Despite their importance, icebergs are rarely represented in ESMs. Freshwater fluxes are often parameterized, neglecting the transport via ocean currents and the heat loss due to iceberg melting. Other models that use an interactive iceberg component are typically ocean-only models, do not represent ice sheets and the atmospheric component explicitly, or are models of intermediate complexity. One reason for this deficiency is the considerable computational costs related to iceberg modeling.

Here, we present the latest version of the Alfred Wegener Institute-Earth System Model (AWI-ESM) with interactive ice sheets and a Lagrangian iceberg model. The iceberg component runs as a submodel of the ocean–sea-ice model FESOM2 with an asynchronous coupling to enable computationally effective simulations with the iceberg-enhanced coupled model. Total execution times can be strongly reduced compared to a non-overlapping execution of the iceberg model with other components. Iceberg meltwater and the associated heat fluxes are coupled to the ocean. The ice sheet is dynamically coupled to the climate components. A new feature of this model setup is the ice sheet-iceberg coupling: Icebergs are drawn from a specific size distribution to match the calving output of the ice sheet model in regions of iceberg discharge. Therefore, discharge-related freshwater fluxes are represented more realistically than in other ESMs.