Variations in the distribution of chlorophyll a and inorganic nutrients around South Georgia, South Atlantic

Abstract

Data collected on four large-scale surveys around the subantarctic island of South Georgia provide information on the variability in the distribution of chlorophyll and inorganic nutrients during the austral summer and winter. During three summer surveys, surface water cholorophyll and nutrient concentrations were highly patchy over scales ranging from a few to hundreds of kilometres. The highest measurement of chlorophyll a was 8 mg m⁻³ and a wide range of nutrient concentrations were found; 5–32 mmol m⁻³ NO₃−N, 1.1–2.2 mmol m⁻³ PO₄−P and 8–60 mmol m⁻³ Si(OH)₄−Si. In winter, chlorophyll and nutrient levels were far more uniform, with chlorophyll concentrations lower and nutrient concentrations generally higher than in summer. The spatial variability in nutrient concentrations was due to a variety of factors acting over a range of scales, however biological processes appeared most important in creating the mesoscale patchiness around the island. Although phytoplankton abundance and nutrient concentrations were not directly correlated, the scales of variability were clearly similar.