Island effects on marine production and circulation around the island of South Georgia, Southern Ocean

An intense phytoplankton bloom is observed annually north of South Georgia, in the Southern Ocean. These blooms sustain the ecosystem around the island and generate a site of strong atmospheric CO2 drawdown. Satellite observations of surface chlorophyll a concentrations and circulation patterns were used to study the variability of phytoplankton blooms in the region. Our analysis reveals a time series of very regular blooms, controlled in space by circulation and in time by surface silicate concentrations, temperature and light. The role of the micronutrient iron was investigated with the coupled hydrodynamic-biogeochemical model ROMS-PISCES. Model results, validated against observations, suggest a continuous supply of iron from the island's shallow shelves that is redistributed in the region by local circulation. Conversely, aeolian sources of iron have a negligible role in the main bloom area, but appear to be more important outside the influence of the South Georgia.