Deep-Sea Research I 51 (2004) 307–332 Geochemical particle fluxes in the Southern Indian Ocean seasonal ice zone: Prydz Bay region, East Antarctica C.H. Pilskaln a, *, S.J. Manganini b , T.W. Trull c , L. Armand c , W. Howard c , V.L. Asper d , R. Massom c a Bigelow Laboratory for Ocean Sciences, 108 McKnown Point Road, West Boothbay Harbor, ME 04575, USA b Woods Hole Oceanographic Institute, Woods Hole, MA 02543, USA c Antarctic CRC/IASOS, University of Tasmania, Hobart, Tasmania 7001, Australia d University of Southern Mississippi, Stennis Space Center, MS 39529, USA Received 8 January 2003; received in revised form 14 October 2003; accepted 21 October 2003 Abstract 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 3300 m 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 to1kmand3–10gm 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 d 15 N time-series data suggest enhanced rates of diatom-POC remineralization in the upper 1000m relative to bio SiO 2 . 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. r 2003 Elsevier Ltd. All rights reserved. Keywords: Biogeochemical cycles; Carbon cycle; Particulate flux; Sediment traps; Antarctic Zone 1. Introduction The Southern Ocean is a critical area for the global exchange between atmospheric carbon dioxide and the large reservoir of dissolved inorganic carbon in the deep ocean (e.g., Gordon et al., 1977, 1981; Takahashi et al., 1981; Sarmiento and Bender, 1994). Biologically pro- duced, sinking particles represent a sink in the global carbon budget whereby atmospheric CO 2 is effectively transferred to the deep ocean and the ARTICLE IN PRESS *Corresponding author. Fax: +1-207-633-9641. E-mail address: cpilskaln@bigelow.org (C.H. Pilskaln). 0967-0637/$-see front matter r 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.dsr.2003.10.010