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

ocean control of carbon dioxide• Demonstration that the long held assumptionthat there is negligible exchange ofatmospheric CO 2exchange with sea-icecovered oceans is incorrect suggests thatclimate models must include both physicaland biological aspects of sea ice gasdynamics to correctly simulate atmosphericcarbon budgets (in collaboration withEuropean researchers; Delille et al., Nature,in review).• Advances in observational strategies forocean biogeochemical characteristics includedi) expansion of the underway observationprogram to measure estimate of gross andnet phytoplankton production from dissolvedO 2/Ar ratios (in collaboration with PrincetonUniversity) and ii) initial deployments ofautonomous profiling Argo floats equippedwith oxygen sensors to monitor oxygenchanges remotely at low cost and in realtime.CO2-02: Carbon ExportProcessesProject leaderTom Trull, UTAS/CMARProject staffL Armand, S Bray, D Davies, W Howard, C Moy,T Remenyi, L Robertson, M Rosenberg, ACE; BGriffiths, D McLaughlin, L Pender, C Rathbone,CMAR; L Forbes, UTAS; P Boyd, S Nodder, NIWAProject AimWe are estimating rates of transfer of particulatecarbon between the ocean surface and thedeep sea, identifying the major processes thatcontrol these rates, and developing conceptualmodels of the sensitivity of these processes toclimate variability and change. A clearer view ofthe role of the ‘biological pump’ (the transfer ofcarbon to the deep sea in particulate form) in theSouthern Ocean in regulating atmospheric CO 2isa necessary step towards the development andverification of reliable carbon cycle models forthe simulation of future atmospheric CO 2levelsand thus future climate change. Understandingof the modern biological pump is also a usefulaid in the interpretation of past changes in theSouthern Ocean environment, and thus theirapplication to estimating future changes.Key achievements in 2005-06• Demonstration that carbon export to theocean interior from the naturally ironfertilised,high phytoplankton biomass watersover the Kerguelen plateau in the Indiansector of the Southern Ocean is large perunit of iron supplied. This contrasts stronglywith the results of short-term artificial ironfertilisation experiments which found lowcarbon export efficiencies. This work wasundertaken in collaboration with the CO2-03:Iron Biogeochemistry project and Europeanresearchers as part of the French KEOPSprogram (Blain et al., Nature, in review).• Demonstration that the carbon isotopiccomposition of Southern Ocean deep watermasses has closely tracked that of the Pacificover most of the past 160,000 years (Moy,Howard, and Gagan, in press, Journal ofQuaternary Science). These new data fromSouth Tasman Rise challenge the traditionalview that the North Atlantic component of the‘conveyor belt’ circulation usually modulatesthe composition of Southern Ocean deepwater masses. Similarly, these resultssuggest that the conveyor belt circulation hasbeen active throughout the late Pleistoceneand not, as thought previously, ‘shut off’during glacial stages.• Advances in observational strategiesfor the measurement of biogeochemicalproperties, including i) development ofviscous polyacrylamide gels for the insitu deceleration and isolation of fragilemarine aggregates for photo-micrometriccharacterisation (Ebersbach and Trull,Limnology and Oceanography, in review); ii)deployment of an in situ settling column to30 Antarctic Climate & Ecosystems CRC - Annual Report 2005-06