The current generation of Earth System Models (ESMs) does not accurately represent the two primary means in which ice is lost from the Antarctic Ice Sheet (AIS) -- through melting at the base of ice shelves floating on the ocean and the calving of icebergs. New capabilities added to E3SM v1.2 for the Cryosphere configuration are described and evaluated, with the aim of improving the representation of ice-ocean interactions with the AIS. A notable new capability is the ability to simulate Antarctic ice-shelf basal melting in an Earth System Model. In addition, we have added the capability to prescribe forcing from iceberg melt, allowing for a realistic representation of the other dominant mass loss process from the AIS.
The future of the AIS has the potential to have broad impacts on global climate, perhaps most notably in contributing to sea-level rise. Lack of explicit representation of the processes by which freshwater (and the associated heat) are transferred from the AIS to the rest of the climate system in an ESM limits the ability to make climate projections that incorporate the impacts of the AIS in a changing climate. In this study, we demonstrate the ability to simulate Antarctic ice-shelf basal melting in E3SM at standard resolution that is in line with present-day observations, an important step towards reducing uncertainties in projections of the Antarctic response to climate change and Antarctica’s contribution to global sea-level rise.
In the Cryosphere configuration of E3SM v1.2, we have added the capability to simulate Antarctic ice-shelf basal melting, which has been implemented through simulating the ocean circulation within static Antarctic ice-shelf cavities, allowing for the ability to calculate ice-shelf basal melt rates from the associated heat and freshwater fluxes. In standard resolution simulations (using a non-eddying ocean) under pre-industrial climate forcing, we find high sensitivity of modeled ocean/ice-shelf interactions to the ocean state, which can result in a transition to a high basal melt regime under the Filchner-Ronne Ice Shelf, presenting a significant challenge to representing the ocean/ice shelf system in a coupled ESM. We show that the inclusion of a spatially dependent parameterization of eddy-induced transport reduces biases in water mass properties on the Antarctic continental shelf. With these improvements, E3SM produces realistic ice-shelf basal melt rates across the continent that are generally within the range inferred from observations.