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

ocean control of carbon dioxidePlans for 2006-07We will lead 3 major field programs in thecoming year:• Development of our 'PULSE' automatedbiogeochemical measurement surfacemooring in the Sub-Antarctic Zone (SAZ) toaugment our deep moored sediment traps,with the addition of additional sensors inearly spring and subsequent service visits inmid-summer and late autumn.• Underway observations from the Frenchresupply vessel l’Astrolabe on upper oceancarbon cycling and continued examinationof phytoplankton responses to oceanacidification.• A month-long study onboard AuroraAustralis of the controls on SAZ productivityand carbon cycling and their sensitivity toclimate change (SAZ-SENSE). This projectwill compare low productivity waters west ofTasmania with higher productivity waters tothe east. It will also expose phytoplanktoncommunities to elevated CO 2levels todetermine their responses, and examineforaminifera (carbonate-shell formingzooplankton) compositions for comparison tosedimentary records of past ocean pH (withfunding from the Australian GreenhouseOffice).We will advance the simulation of SouthernOcean biogeochemical cycles, phytoplanktonproduction, and microbial ecosystem structure,with emphasis on:• Controls on elevated phytoplanktonaccumulation over the naturally iron-fertilisedKerguelen plateau.• Interactions between climate warming andanthropogenic CO 2uptake in terms of theiraffect on ocean acidity.Ongoing synthesis and delivery of our researchwill include six presentations at the internationalScientific Committee on Antarctic Research(SCAR) meeting in Hobart in July 2006, andpublication in peer-reviewed journals. Some ofthe contributions currently in review are detailedin the Project reports.Project reportsCO2-01: Carbon uptake in theSouthern OceanProject leaderBronte Tilbrook, CMARProject staffM Pretty, K Paterson, CMARProject AimThis project will describe the variability andlarge-scale biological and physical drivers ofthe air-sea exchange of carbon dioxide (CO 2)in the Southern Ocean, south of Australia. Theresults will better define the critical role of theSouthern Ocean in controlling atmosphericCO 2concentrations, and allow more robustpredictions of how the Southern Ocean uptakemay be altered in future under changed climaticconditions. The research will contribute to amajor new initiative to determine regional andglobal scale carbon budgets, which are requiredto develop useful strategies to manage futureCO 2emissions and their environmental impacts.Key achievements in 2005-06• Analysis of the full hydrographic sectioncompleted in 2005 from Australia toAntarctica along the WOCE-CLIVAR I9S linesouth of Fremantle revealed increases in CO 2and decreases in dissolved O 2concentrationsfor mode and intermediate waters, comparedto 1995 results from the same sectionobtained by the USA. These results areconsistent with continued CO 2uptake andstorage in sub-Antarctic waters leading toa pH decrease in the region. The oxygenchanges are consistent with previous workfrom the Biogeochemical Simulation Projectsuggesting that the overturning circulationthat carries CO 2and O 2into the ocean interioris slowing in response to climate warming,but could also represent shorter term climateand ocean variability.Antarctic Climate & Ecosystems CRC - Annual Report 2005-06 29