Datensatz

Zusammenfassung

Intense atmosphere-ocean-ice interactions in the Ross Sea produce the most saline dense shelf waters around the Antarctic, supplying the lower limb of the global overturning circulation. Over the last 50 years, freshening in the Ross Sea shelf water contributed to a decrease in Antarctic Bottom Water (AABW) formation. The recent rebound of shelf water salinity in the Ross Sea since 2012 has been observed and suggested to be driven by wind anomalies. However, lack of observation on the continental shelf prevents a quantitative assessment of shelf water salinity response to wind and other atmospheric forcing. Here, we design perturbation experiments to investigate the causes of the observed salinity rebound using a global ocean-sea ice model. Our results show the recent salinity rebound in the whole water column (0-900 m) of the western Ross Sea was supplied by brine rejection from the surface through convection, which is induced by increased sea ice formation. We further find this increased sea ice formation was triggered by the combined effect of anomalous wind stress and surface heat flux, which have nearly equal impacts on salinity but through different mechanisms. Weakened easterlies reduced sea ice import into the western Ross Sea and decreased the local sea ice thickness and concentration in winter, which promotes sea ice formation. A negative heat flux anomaly decreased the surface temperature, leading to increased sea ice production in winter. The two mechanisms identified here will help to understand the implication of climate change on observed and projected changes in AABW.