Discussions on the ISMIP7 Antarctic ice-ocean forcing protocol

In past decades, substantial advances on understanding ocean–ice-shelf interactions have been made, and a number of parameterisations that provide sub-shelf melting for ice sheet modelling studies have been developed. Through ISMIP6, it was found that the choice of parameter values in melt parameterisations can influence the order of magnitude of melt rate changes in projections. Moreover, it has been shown that constraining those parameters with present-day observations is not sufficient to constrain melt rate changes under future warming. For ISMIP7, we hence propose a “come-as-you-are” approach for the choice of the sub-shelf melt parameterisation, but suggest a protocol for calibrating parameters using ocean model simulations and observations that show large changes in cavity temperatures as additional constraints. This is embedded into an updated and revised protocol for processing CMIP model data for the ISMIP7 Antarctic ice-ocean forcing protocol.