MODELING THE ICE OCEAN PLANKTON INTERACTIONS IN THE SOUTHERN-OCEAN

Our goal is the study of interactions between sea ice and ocean and of their influence on planktonic communities. We use a physical model wh ich includes explicitly melting dynamics and mixed-layer physics. A on e-dimensional model of the water column with a k-l turbulent closure i s applied. The sea-ice model is the one proposed by Semtner (1976); we add a parameterization of leads. We enlighten the importance, in this kind of model, of the sharing of the energy between lateral and basal meltings. The biological model comprises two state variables: phytopl ankton and zooplankton biomasses. Melting induces a persistent shallow mixed layer and thus appropriate conditions for primary production. I f ice melting is present, high biomasses are possible even with high l osses. The absence of ice nearly forbids a massive bloom to form. Some sensitivity studies have shown that grazing pressure is a key factor governing the evolution of biomasses. The biomasses are also sensitive to little modifications of the photosynthetic production. The initial amount of phytoplankton or the presence of ice algae seems to be of l esser importance.