Downward fluxes of biogenic material in Bransfield Strait, Antarctica

Abstract

Time-series sediment traps were deployed to investigate the temporal evolution of particle fluxes in eastern and central Bransfield Strait, from December 1999 to December 2000. Particle fluxes showed large seasonal variation at both trap sites. In eastern Bransfield Strait, summer mass fluxes were two orders of magnitude higher than winter mass fluxes, while in central Bransfield Strait, almost 99 % of the annual mass flux (33 g m-2) was collected in a 40-day period from December to January. Export flux also exhibited a high regional variability. This regional variability is probably due to central Bransfield Strait's strong surface current, which carries most settling particles produced in the surface waters away from the mooring site during the low summer flux period. The relatively low biogenic silica to organic carbon ratios (a range of 0.29-1.4) and high lithogenic fluxes (41 % of total mass flux) indicate that the growth of phytoplankton is not limited by the micronutrient iron in eastern Bransfield Strait. The annual flux of organic carbon in eastern Bransfield Strait was 6.8 g C m-2, which is three times higher than the flux measured in central Bransfield Strait (2.2 g C m-2). Organic carbon flux in eastern Bransfield Strait is relatively high for the Southern Ocean, possibly due to fast-sinking fecal pellets that lead to less decomposition of organic material in the water column. Approximately 7.2 % of the organic carbon produced at the surface in eastern Bransfield Strait is exported to a depth of 678 m. This exceeds the maximum export of primary production to a depth of 1,000 m in the Atlantic and Southern Oceans.