Interannual variation of particle fluxes in the eastern Bransfield Strait, Antarctica: A response to the sea ice distribution

Abstract

Time-series sediment traps were deployed to investigate the temporal evolution of particle fluxes in the eastern Bransfield Strait over a 3-year period, from December 1998 to December 2001. Particle fluxes showed large seasonal and interannual variations. In 1999 and 2000, a seasonal trend of mass fluxes was characterized by highly elevated mass fluxes in the summer season, greater than 300 mg m −2 d −1, two orders of magnitude greater than winter mass fluxes. Such high summer fluxes were not observed in 2001, however, and seasonality was also significantly reduced. The absence of a high summer flux in 2001 might have been due to an abnormal expansion of sea ice to the trap mooring site during the 2001 summer season. The large interannual variation in particle flux is closely related to annual changes in sea ice cover in the eastern Bransfield Strait, which limits phytoplankton productivity in the surface waters. There is a lag of about 1 month between the surface water productivity and the export production in the eastern Bransfield Strait. The delay in the export production might have been due to the favorable environmental conditions for phytoplankton growth in the early summer when most primary production is stored in phytoplankton biomass, and few organic particles sink into the deep ocean. An average biogenic silica:organic carbon (Si:C) ratio of 1.5 was obtained from trap material collected at a depth of 678–1034 m, lower than the ratio obtained from the marginal winter sea ice zone of the Atlantic section and the Antarctic zone of the Pacific section. To produce a Si:C ratio of 1.5 at a depth of 678–1034 m from the surface water ratio of 0.52, at least 65% of the surface organic carbon must be remineralized during the descent to 678–1034 m. The 3-year mean of annual organic carbon fluxes measured in the eastern Bransfield Strait was 4.21±3.16 g C m −2, about two times higher than that of the central Bransfield Strait (2.84±3.33 g C m −2) and an order of magnitude higher than that of the western Bransfield Strait (0.35 g C m −2).