Annual report 2005-06.indd - Antarctic Climate and Ecosystems ...

ocean control of carbon dioxideseparate particles by sinking rates – a keycontrol on carbon export (in collaborationwith American researchers in the ‘VERTIGO’Vertical Flux in the Global Ocean program);iii) deployment of the PULSE mooring– the first surface-mooring in the openSouthern Ocean based on an innovativeshock-dampening design, with the goal ofobtaining continuous observations of mixedlayer depth, light levels, and in later yearsphytoplankton and nutrient concentrationsto address the role of surface dynamicsin the control of ecosystem structure andcarbon export; iv) development of analyticalmethods for particulate carbonate andparticulate silicate concentrations; and v)critical reviews of sediment trap techniques(Buesseler et al., Journal of Marine Research,in review) and the application of 234 Thdisequilibria to the estimation of carbonexport (Buesseler et al., Marine Chemistry,2006).CO2-03: Iron biogeochemistryProject leaderAndrew Bowie, ACE CRCProject staffS Bray, T Remenyi, L Robertson, ACE; E Butler,CMAR; P Boyd, NIWAKey achievements in 2005-06• Demonstration that elevated phytoplanktonbiomass over the Kerguelen plateau in theIndian sector of the Southern Ocean as seenin satellite remote sensing images is fuelledby iron inputs from deep waters, and thusthis region represents an area of naturalpersistent iron fertilisation that can informdebate about the role of iron in the control ofatmospheric CO 2. This work was undertakenin collaboration with the Carbon ExportProcesses project and European researchersas part of the French KEOPS program (Blainet al., Nature, in review).• Demonstration that dissolved ironconcentrations are low in surface watersalong the WOCE/Clivar transect fromTasmania to Australia with early springdepletion in polar waters, but evidenceof continued inputs into summer in sub-Antarctic waters from sources to the north(Sedwick et al., Deep-Sea Research, inreview).• Advances in observational strategies for themeasurement of biogeochemical properties,including i) international intercomparison ofiron analytical techniques (Bowie et al., 2006)and ii) trace-metal clean size-fractionationfiltration techniques.Project AimWe are evaluating the importance of iron andother trace micronutrient elements in drivingSouthern Ocean biogeochemical cycles. Theresearch team will map the distribution ofdissolved iron in waters south of Australia,fingerprint supply and removal mechanisms,and quantify trace element limitation ofphytoplankton growth and community structurein sub-Antarctic ecosystems. This project willfeed vital information on the prevalence andflux of trace elements into biogeochemical andecosystem models of the region, thus allowing aprediction of the role of Southern Ocean biologyin past and future regulation of atmospheric CO 2through ecosystem control of carbon transferto the deep ocean. The research will assessthe risk and efficacy of proposals to increasecarbon sequestration through intentional ironfertilisation of the Southern Ocean.Antarctic Climate & Ecosystems CRC - Annual Report 2005-06 31