The distribution of biogenic silica and the composition of particulate organic matter in the Weddell—Scotia Sea during spring 1988

Abstract

During EPOS 2 (European Polarstern Study, leg 2, 26 November 1988–5 January 1989 the distribution of biogenic silica (BSi) was determined from the surface to 600 m along two transects (49°W and 47°W) spanning the Scotia Sea, the Weddell—Scotia Confluence (WSC) and the marginal ice zone (MIZ) of the Weddell Sea. Particulate organic carbon (POC), particulate organic nitrogen (PON) and chlorophyll a concentrations were determined in parallel in surface (10m) samples. In the 0–100 m layer, the distribution of particulate biogenic silica (BSi) showed little correlation with the meltwater field in late November. High BSi concentrations were measured at the end of November in the Weddell—Scotia Confluence (maximum 4.8 μmol l −1), and early in January in the Antarctic Circumpolar Current (maximum at 8.2 μmol l −1) where the wind-mixed layer was only 35 m, creating favourable conditions for phytoplankton growth. However, maximum and mean biogenic silica values remained fairly low as compared with those reported for the Ross Sea. This relatively low silica content of the 0–100 m layer appears to be mainly due to intense grazing which resulted in rapid exportation of particulate material towards the deeper layers. The mean POC/PON molar ratio was 5.5, i.e. significantly lower than the usual Redfield ratio. BSi/POC molar ratios ranged from 0.01 to 0.61, the highest values being found in the Scotia Sea, where siliceous phytoplankton was dominant. The high BSi/POC ratios confirm that diatoms in Antarctic Ocean are able to incorporate unusually high amounts of Si relative to carbon, as compared with other ecosystems.