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An integrated approach to assess carbon dynamics in the Southern Ocean

Antarctica phase IV (1997-2000)

An integrated approach to assess carbon dynamics in the Southern Ocean

Coordinator

Dr Frank Dehairs
Vrije Universiteit Brussel
Laboratorium voor Analytische Scheikunde (ANCH)
Pleinlaan, 2
B-1050 BRUSSELS
Phone: +32 (0)2 629 32 60
Fax: +32 (0)2 629 32 74
E-mail: fdehairs@vub.ac.be
www.vub.ac.be/infovoor/onderzoekers/research/
team.php?team_code=ANCH

Promotors

Dr Christiane Lancelot
Université Libre de Bruxelles - C.P. 221
Microbiologie des Milieux Aquatiques
Campus de la Plaine
Bd. du Triomphe
B-1050 BRUSSELS
Phone:+32 (0)2 650 59 88
Fax: +32 (0)2 650 59 93
E-mail: lancelot@ulb.ac.be
www.ulb.ac.be/rech/inventaire/unites/ULB115.html

Prof. Luc André
Royal Museum for Central Africa
Dept of Geology and Mineralogy
Steenweg op Leuven, 13
B-3080 TERVUREN
Phone: +32 (0)2 769 54 59
Fax: +32 (0)2 769 54 32
E-mail: landre@africamuseum.be
www.africamuseum.be/research/projects/prj_detail?prjid=395

Dr Michel Frankignoulle (Université de Liège)
Université de Liège
Unité d'Océanographie chimique
Sart Tilman - Physique B5
B-4000 LIEGE
Phone: +32 (0)4 366 33 26
Fax: +32 (0)4 366 23 55
E-mail: michel.frankignoulle@ulg.ac.be
www.ulg.ac.be/cms/c_566135/en/godavari-a-long-gentle-river

Dr Eric Deleersnijder
Université Catholique de Louvain
Institut d'Astronomie et de Géophysique G. Lemaître
Chemin du Cyclotron, 2
B-1348 LOUVAIN-LA-NEUVE
Phone: +32 (0)10 47 26 76
Fax: +32 (0)10 47 47 22
E-mail: ericd@astr.ucl.ac.be
www.astr.ucl.ac.be/index.php?page=ResearchModels

Topics

This research attempts to determine the role - CO2 source or sink - of the Southern Ocean on a regional and seasonal scale by implementing an integrated multidisciplinary approach which combines in situ measurements, studies of process in laboratory controlled conditions and numerical computation. It approaches the whole of the processes which govern the cycle of carbon in the Southern Ocean, from exchanges of CO2 at the air/sea interface until to accumulation of carbon in the sediments. It is based on a mechanistic scientific approach which aims at improving comprehension of the production process and of mineralisation of carbonated biomass in surface water as well as export towards the deep ocean. In particular, the roles of light and the availability in nutrients (major and minor) in the determination of the dominant phytoplanktonic community, and thus of the dynamics of the associated food chain and the carbon exportation, will be studied in areas dominated by various phytoplanktonic communities, namely the diatoms, the colonies of Phaeocystis and the nanophytoplankton. The role of aggregates as carbon conveyors, from surface to the deep water and the sediments, will be investigated with special attention to the following processes : the bacterial mineralisation of aggregates and the production and fate of the barite proxy.

The use of the barite as tracer of the exported carbon flux will be evaluated in order to improve the existing transfer functions. Acquired knowledge will then be integrated in a 1D physical and biogeochemical model able to simulate the cycle of carbon as well associated biogenic elements (N, Si, Fe, Mn, Ba) in the whole water column of the Southern Ocean over a seasonal cycle. All together, this study will contribute to establish a diagnostic and predictive model which will be used to evaluate the role of the Southern Ocean in a global perspective.

Goals

This integrated study has as overall objective to determine the role of the Southern Ocean - CO2 source or sink - on a seasonal and regional scale. It more specifically aims at bringing an answer to the following questions :

  • Which are the CO2 source and sink areas in the Southern Ocean system, and which is the net flux of CO2 between the ocean and the atmosphere?
  • Which are the biological and physicochemical mechanisms controlling the distribution of CO2 partial pressure (pCO2)?
  • Which are the mechanisms governing the production and the mineralisation of organic carbon in surface waters?
  • By which mechanisms do light, inorganic nutrients (nitrate, ammonium, silica) and trace elements (Fe, Mn) control the photosynthesis and the growth of the three key-component of the phytoplankton of the Southern Ocean (diatoms, Phaeocystis, nanophytoplankton)?
  • Which are the mechanisms which determine the fate of organic carbon in surface water and in particular the factors controlling the formation of aggregates derived from the controlling the formation of aggregates derived from the phytoplankton and their mineralisation by the micro-organisms which adhere to it?
  • Which are the mechanisms of transformation of organic carbon during its transfer from surface to the sediment, in particular those implied in the degradation and the mineralisation of the aggregates in the first 500 meters of the water column?
  • Up to what point are the geochemical tracers such as Ba-barite valid "proxies" of the export production?
  • Up to what point the mechanistic model CLIO-1D/SWAMCO whose numeric code results from the assets of the project, allows the evaluation of the role - sink or source of CO2 - of the Southern Ocean at seasonal and regional scale?

The project combines the specific expertise of different research groups in Belgium. The expertise of the Royal Museum for Central Africa-Section of Mineralogy and Petrography (Luc André) is situated within the research of Barite geochemistry. Specific research items include:

  • Kinetics of the uptake of tracers (Sr, Nd, Ce, Th, Pb) by suspended matter and aggregates by means of isotopic dilution techniques.
  • Kinetics of the uptake of tracers by aggregates by means of in vitro incubation experiments.
  • Geochemical composition and vertical distribution of barite.
  • Barium-barite geochemical and isotopic fractionation between particulate phase (sediment and suspended matter) and sea water.
  • Morphology and geochemical composition of sedimentary barite.

Specific expertise

Dr F. DEHAIRS: New and export production

  • Space and time differentiation of phytoplankton functionality.
  • Phytoplankton nitrogen uptake regime.
  • Role of aggregates in the formation of barite.
  • Kinetics of the uptake of Ba and other tracers (Sr, Nd, Ce, Th, Pb) by suspended matter and aggregates by means of isotopic dilution techniques (on board experiments).
  • Dynamics of Ba uptake and remineralization in the water column.
  • Space variability of BaSO4 saturation rate.
  • Ba-based transfer functions for estimating export production.
  • Overall synthesis of results of the integrated project.

Dr Ch. LANCELOT: Study and modellisation of the planktonic system

  • Physiological parameters characteristic of carbon metabolism in diatom- and Phaeocystis-dominated communities by means of an innovative protocol combining 14C labelling and biochemistry.
  • Diatom silica uptake (32Si radio-tracer method).
  • Assimilation and adsorption of Fe and Mn by the phytoplankton.
  • Diatom/Phaeocystis-derived aggregate formation and microbial transformation.
  • Sedimentation of diatom/Phaeocystis-derived material.
  • Extension and upgrading of the mechanistic biogeochemical model SWAMCO.

Prof. L. ANDRÉ: Barite geochemistry

  • Kinetics of the uptake of tracers (Sr, Nd, Ce, Th, Pb) by suspended matter and aggregates by means of isotopic dilution techniques.
  • Kinetics of the uptake of tracers by aggregates by means of in vitro incubation experiments.
  • Geochemical composition and vertical distribution of barite.
  • Barium-barite geochemical and isotopic fractionation between particulate phase (sediment and suspended matter) and sea water.
  • Morphology and geochemical composition of sedimentary barite.

Dr M. FRANKIGNOULLE: Air/sea exchanges

  • Methodology for the assessment of pCO2, pH and O2 in the polar environment.
  • CO2 fluxes through the ocean/atmosphere interface.
  • Vertical distribution of carbon and oxygen in relation to organic matter production and mineralization.

Dr E. DELEERSNIJDER: 1-D modelling of the sea-ice and water column

  • One-dimensional adaptation of the CLIO-1 model and validation.
  • On-line coupling of the SWAMCO and CLIO-1D models and calibration.

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