Local and remote processes' impacts on dense water formation (Deliverable D1.10)

The dense shelf water (DSW) formed around Antarctica is a source of the coldest waters spreading through the ocean's abyss, the Antarctic Bottom Water (AABW) (e.g., Orsi et al., 1999). The formation is associated with recurring polynyas in four main areas of the continental shelf, including the southern Weddell Sea, the Ross Sea, Prydz Bay, and Adélie Land (Solodoch et al., 2022).
Polynyas open up when sea ice is pushed away from the coast by winds or ocean currents. In cold months, the exposed ocean surface freezes again, and salt is rejected into the ocean as brine. The large brine injection related to intense sea ice production (SIP) increases the ocean salinity, forming High Salinity Shelf Water (HSSW), one type of DSW with surface freezing temperatures. In the Southern Ocean, most polynyas occur over the continental shelf where HSSW sinks and follows the bathymetry along the bottom. HSSW can flow offshore and slide down the continental slope, mixing with ambient waters along its path until it reaches the equilibrium depth as AABW. HSSW can also flow into the ice shelf cavity, where the freezing temperature is lower than at the surface due to the pressure effect. There, it causes melting, and the mixture with Glacial Melt Water (GMW) generates the supercooled (colder than surface freezing temperature) and slightly fresher Ice Shelf Water (ISW), a second flavor of DSW.
We used previously validated model results (van Caspel et al., 2024; D1.7) to show that DSW in the Weddell and Ross Seas persists year-round, whereas it is absent in summer at the other two formation sites. In the Weddell Sea and Ross Sea, the maximum volume of DSW available during the formation season is correlated with the minimum volume of the following year. This finding indicates that, in these areas, the annual formation rate plays an important role in the DSW reservoir. The annual increase in DSW volume correlates with the local accumulated SIP in polynyas in the Weddell Sea and Prydz Bay. In most cases, the salinity of the surface and/or subsurface waters entering each region from remote areas has a significant correlation with the salinity of the DSW formed, but only in Prydz Bay the correlation is higher than 0.5.

Data underlying this deliverable: https://zenodo.org/records/15189061