Geochemical particle fluxes in the Southern Indian Ocean seasonal ice zone: Prydz Bay region, East Antarctica

Time-series sediment traps were deployed between December 1998 and January 2000 and from March 2000 to February 2001 at two offshore Prydz Bay sites within the seasonal ice zone (SIZ) of the Southern Indian Ocean located between 62-63°S and 73-76°E to quantify seasonal biogeochemical particle fluxes. Samples were obtained from traps placed at 1400, 2400, and 3400m during the first deployment year (PZB-1) and from 3300m in the second deployment year (PZB-2). All geochemical export fluxes were highly seasonal with primary peaks occurring during the austral summer and relatively low fluxes prevailing through the winter months. Secondary flux peaks in mid-winter and in early spring were suggestive of small-scale, sea-ice break-up events and the spring retreat of seasonal ice, respectively. Biogenic silica represented over 70% (by weight) of the collected trap material and provided an annual opal export of 18gm^-2 to 1km and 3-10gm^-2 to 3km. POC fluxes supplied an annual export of approximately 1gm^-2, equal to the estimated ocean-wide average. Elevated particulate C_org/C_inorg and Si_bio/C_inorg molar ratios indicate a productive, diatom-dominated system, although consistently small fluxes of planktonic foraminifera and pteropod shells document a heterotrophic source of carbonate to deeper waters in the SIZ. The observation of high Si_bio/C _org ratios and the δ¹⁵N time-series data suggest enhanced rates of diatom-POC remineralization in the upper 1000m relative to _bioSiO₂. The occurrence in this region of a pronounced temperature minimum, associated with a strong pycnocline and subsurface particle maximum at 50-100m, may represent a zone where sinking, diatom-rich particulates temporarily accumulate and POC is remineralized.