Ice formation and hydrodynamics of the Weddell Sea: a modelling approach

In the Southern Ocean, the formation of deep water and the convective movements are influenced by inter-annual variability of ice production/coverage modulating the magnitude of air/sea fluxes. The study of these important phenomena needs an accurate representation of the sea surface coverage by the ice pack. A one-dimensional thermodynamic model based on Semtner's approach associated with a horizontal transport component is used to compute the sea ice thickness and extent. A visco-plastic ice rheology parameterization is used to model the ridging of the ice pack. Turbulent surface heat and momentum fluxes over ice and open areas are classically computed. The sea ice and leads are connected to the deep ocean through a mixed layer. The heat and salt fluxes between ice and water column are explicitly taken into account. Finally, a 3D ocean circulation model of the complete Southern Ocean Atlantic sector is run to provide velocity fields for the computation of the ice dynamics. Passive microwave ice concentration observation are used to calibrate the ice model. Scarce ice thickness data are also used for that purpose. The percentage of ice coverage and the ice thickness are two outputs of the model available for operational purposes such as ice management. This work is a step in the development of a fully-coupled ocean circulation/sea ice model developed for the Southern Ocean. It is also planned to use it for environmental purposes such as studying primary production in the Weddell and Ross Seas. Doing so, a number of biological or environmental state variable can be added to the model.