444 / 2024-09-17 10:05:09

Salinity and temperature budgets in the Ross Sea inner continental shelf

Tracer budgets,Climatology,Box Model

The Ross Ice Shelf (RIS) polynya is one of the major production sites of the Dense Shelf Water (DSW), which is the precursor of the Antarctic Bottom Water that fills the deep ocean basin. Over the Ross Sea continental shelf, DSW is modified by local and remote water masses such as the Ice Shelf Water, Circumpolar Deep Water and the remnant summer surface water; the production rate of Antarctic Bottom Water is thus modulated by the exchange of DSW with these water masses.



Using a combined dataset of historical bottle/CTD measurements, autonomous profiling floats, seal-borne CTD tags and glider surveys, this study generates a monthly climatology of temperature and salinity in the RIS polynya and inner continental shelf to reveal the seasonal evolution of water masses and water column stratification. The climatology shows an evident annual cycle in the RIS polynya, where surface stratification begins to develop in November and reaches maximum (N²=2×10^-4 s^-2) in January, then decreases and drops below 1×10^-5 s^-2 in May. During austral summer, air-sea fluxes raise surface bulk temperature to -0.5°C in the inner continental shelf, where the heat is preserved in subsurface layers over a few months. Strong glacial influence is found in the RIS polynya, where salinity is consistently lower (by up to 0.05 PSU) compared with the inner continental shelf. No clear evidence of Circumpolar Deep Water influence is found in the RIS polynya.



Using a reduced-physics box model, salinity and temperature budgets in the RIS polynya and the RIS cavity is estimated based on the newly formed climatology. Results reveal a total heat loss rate of 7×10¹² W from the cavity sea water to the ice shelf, which is balanced by advective heat flux driven by exchange flow. Heat loss to the RIS is accompanied by glacial basal melting, which reduces the formation rate of DSW in the RIS polynya and weakens the exchange flow. This is a potential negative feedback mechanism that regulates DSW production in the Ross Sea continental shelf.