Effects of a landfast ice representation on Antarctic shelf water properties and ice shelf melt simulated by NEMO4-SI³

The formation of dense water in the Southern Ocean plays a key role in the global ocean overturning circulation, affecting the distribution of heat, carbon, oxygen and nutrients across the World Ocean. However, its representation in large-scale ocean–sea ice models used in climate studies remains biased. These models often produce dense water in the wrong locations and for incorrect reasons. We hypothesize that this partly stems from a poor representation of coastal polynyas and their drivers, particularly landfast ice. In a recent study, we introduced a velocity-restoring method to represent Antarctic landfast ice in the NEMO4-SI³ ocean–sea ice model and demonstrated its essential role in shaping coastal polynyas and controlling sea ice production. Here, we investigate the impact of this landfast ice representation on Antarctic shelf water properties and ice shelf melt. When the landfast ice scheme is activated, continental shelf waters densify in some coastal polynya areas, as expected. However, freshening is also observed beneath extensive landfast ice tongues, influencing salinity in several downstream polynyas. At a circumpolar scale, landfast ice improves the realism of bottom shelf water salinity and temperature. Notably, changes in mixed layer depth modulate the exchanges between the continental shelves and the open ocean, resulting in enhanced ice shelf melt. Overall, we show that representing landfast ice impacts the simulated ocean stratification, and formation and transformation of key Antarctic water masses. Our results thus further highlight the need for a physically-based representation of Antarctic landfast ice in Earth system models.