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 a nd forced by an annual cycle of solar radiation and mixed layer depth. Sens itivity experiments indicate that disregarding remineralization and dissolu tion of silica does not affect phyto- and zooplankton biomass significantly . Experiments with different half saturation constants of silicate uptake i ndicate that values between 4 and 8 are reasonable for the plankton communi ty at the Antarctic Polar Front. The role of iron limitation is investigate d using different Si:N uptake ratios and reduced growth rates. While reduci ng the maximum growth rate leads only to slightly lower phyto- and zooplank ton biomasses, different Si:N uptake ratios affect the development and maxi mum 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. (C) 2000 Else vier Science B.V. All rights reserved.