Plankton dynamics in frontal systems of the Southern Ocean

A Biological Model of the Antarctic Polar Front (BIMAP) has been developed. The model comprises two biochemical cycles, silica and nitrogen, and five to seven compartments. Model runs are initialized using the WOCE data set and forced by an annual cycle of solar radiation and mixed layer depth. Sensitivity experiments indicate that disregarding remineralization and dissolution of silica does not affect phyto- and zooplankton biomass significantly. Experiments with different half saturation constants of silicate uptake indicate that values between 4 and 8 are reasonable for the plankton community at the Antarctic Polar Front. The role of iron limitation is investigated using different Si:N uptake ratios and reduced growth rates. While reducing the maximum growth rate leads only to slightly lower phyto- and zooplankton biomasses, different Si:N uptake ratios affect the development and maximum of plankton biomass significantly. Specifically, primary production and plankton biomass are strongly reduced by increasing the silica to nitrogen uptake ratio to values greater than 2. An Si:N uptake ratio between 2 and 4 appears to be reasonable for the region of the Polar Front.