Pilskaln¹, Cynthia H., Thomas W. Trull² and Paul J. Treguer³

¹Bigelow Laboratory for Ocean Sciences, 180 McKown Pt. Rd., West Boothbay Harbor, ME 04575 USA, Tel: 207-633-9660, E-mail: cpilskaln@bigelow.org, ²Antarctic CRC, University of Tasmania, GPO Box 252-80, Hobart, Tasmania 7001, Australia and ³Institut Universitaire European de la Mer, UMR 6539, Technopolec Brest-Iroise, Plouzane 29280, France

Zonal variability in carbon export and mesopelagic remineralization in the Southern Indian Ocean sector: Synthesis and global implications

Substantial international efforts over the past 10 years have been directed at quantifying carbon export dynamics in the Southern Indian Ocean and examining the role of this vast sector in Southern Ocean carbon cycling budgets. The research efforts include the Australian Subantarctic (SAZ) Program along 140˚E, the French ANTARES/KERFIX Programs focused on the Subtropical Zone (STZ), the SAZ, and the Polar Frontal Zone (PFZ) in the Kerguelen Plateau region, the joint US-China-Australia program in the Antarctic Zone (AZ) near Prydz Bay, and the SOIREE Iron Release Experiment. Results document major differences as well as some unexpected similarities between the circumpolar zones. For example: despite dramatically different plankton communities and seasonal nutrient dynamics, the SAZ deepwater export of POC is very similar to the PFZ but seasonal patterns vary. POC fluxes in the open-ocean AZ display strong interannual variability, associations with carbonate-bearing heterotrophs, and a lack of contribution from sea-ice algae. Additionally, the role of bacteria in the remineralization of sinking POC is much greater in the STZ compared to the PFZ resulting in higher benthic carbon accumulation rates in the PZF. A synthesis of Southern Indian Ocean carbon export and remineralization data sets from >1 km is presented and compared to JGOFS Pacific and Atlantic sector data, with an emphasis on the efficiency of carbon remineralization in mesopelagic waters and its variability within the circumpolar zones of the Southern Ocean.