Antarctic marginal ice zone in the CMEMS GREP ensemble reanalysis product

The variability of ice-covered area in the Southern Ocean plays a crucial role in the modulating the exchange of heat, mass and momentum between ocean and atmosphere. Knowledge of ice properties and their variability is necessary for an adequate simulation of those fluxes. Global ocean reanalyses provide consistent and comprehensive records of ocean and sea ice variables and are therefore of pivotal significance for climate studies, particularly in data-sparse regions such as Antarctica.

We present the temporal and spatial variability of Antarctic sea ice area in the CMEMS ensemble of global ocean reanalyses (GREP), over the 1993-2019 period. We assess the accuracy of GREP in reproducing the evolution in time and space of Antarctic total sea ice and discriminating between sea ice classes, the marginal ice zone (MIZ) from consolidated pack ice. GREP provides consistent estimates of recent changes in the Antarctic sea ice area and propery reproduces observed interannual and seasonal variability, linear trend, as well as record highs and lows. For sea ice classes, the ensemble spread is comparable to the spread among observational estimates. GREP is shown to properly represent the variability of pack and MIZ areas during the growing and melting seasons, as well as their minima and maxima. More evident discrepancies between GREP and satellite products occur during summer, when the spread among individual ORA increases. Nonetheless, due to minimization of the single errors, the ensemble mean provides the most consistent and reliable estimates. 

Our analysis suggests that GREP can be used to get a robust estimate of current Antarctic sea ice state and recent trends in sea ice area and extent.