Impact of drifting icebergs on surface phytoplankton biomass in the Southern Ocean: Ocean colour remote sensing and in situ iceberg tracking

Icebergs that calve from the Antarctic ice shelves and drift in the Southern Ocean melt to deliver fresh water, dust and minerogenic particles to the surface ocean along the icebergʹs path. Each of these components may have an effect on growth conditions for phytoplankton, as might the mechanical effects of the iceberg keel disturbing the water. Although anecdotal and small-scale surveys suggest that drifting icebergs increase local primary production, no large-scale studies have been reported. An analysis of satellite and automated iceberg tracking data from the Weddell Sea, covering the months October to March, from 1999 to 2004, showed that the probability of increased surface phytoplankton biomass was up to one-third higher in the wake of a tracked iceberg compared to background biomass fluctuations. Only during the month of February were the effects of icebergs on surface biomass likely to be negative, whereas background biomass fluctuations were likely to be negative during March. These results confirm icebergs as a factor affecting phytoplankton in the Southern Ocean and highlight the need for detailed process studies so that responses to future changes in the Antarctic ice sheets may be predicted.