Abstract:

Based on seal CTD data obtained in mid-western areas of Vincennes Bay during March–April 2012, the
effect of double diffusive convection during the evolution of the seawater thermohaline structure during the
early freezing period was evaluated. Results showed that the effect of double diffusion convection was substantial.
The proportion of “diffusion convection” throughout the entire water column was >50%, and strong
“diffusion convection” persisted in the deep water from 500 to 800 dbar. The proportion of “salt finger convection”
in the water column was ≤10% and it occurred in the mid-layers between 300 and 500 dbar. As the
Antarctic winter progresses, brine rejection during sea ice formation makes the water increasingly gravitationally
unstable. “Diffusion convection” produces upward fluxes of heat and salinity. The heat flux is in the
range of 0.02–0.5 W·m⁻², and the average salinity flux is about 10⁻⁸ m·s⁻¹. “Salt finger convection” produces
downward fluxes of heat and salinity; the average heat flux is about −0.5 W·m⁻² and the average salinity flux
is about −10⁻⁸ m·s⁻¹. During the early freezing period, continuous cooling and brine rejection force the production
of dense water with low temperature and high salinity. Double diffusion convection (mainly diffusive
convection) reforms the water properties, making the entire water column denser. Therefore, the contribution
of double diffusion convection on the formation of dense shelf water in Vincennes Bay is crucial.

Key words: shelf water, evolution of seawater, double diffusion convection, diffusive convection, Vincennes
Bay, Antarctica