Duration of the project: 01/12/2000 - 31/11/2004

Budget: 1,466,414.14 EURO

Key words: Southern Ocean; Climate Change; air-sea CO2 fluxes; biological carbon pump; coupled hydrodynamic - biogeochemical modeling

Context

Because of unique hydrodynamic and ecological features the Southern Ocean plays a key role in the global air-sea exchange of CO2. A sustained supply of essential nutrients (N, P, Si) through deep-water upwelling ensures the great potential of the SO to further enhance CO2 uptake via the biological pump. However, in the HNLC (High Nutrient Low Chlorophyll) waters of the modern Southern Ocean this does not occur because biological production is iron limited. Future climate-driven changing patterns in water circulation, eolian transport of continental dust, sea ice extent and lithogenic matter input from Antarctic continent and/or shelf and slopes areas could modify natural fertilisation patterns of the Southern Ocean, impacting on the ecosystem structure and function, the export production and the air-sea CO2 flux. This will likely induce a feedback to climate.

Description of the project

This project proposal focuses on the role of the Southern Ocean in Global Change. The research is conducted by BELCANTO (BELgian research on Carbon uptake in the ANTarctic Ocean), an interdisciplinary network of biologists, geochemists, physical and ecological modelers. Focus is on the development of geochemical proxies and numerical tools for understanding the present-day functioning of the biological carbon pump in the iron-limited Southern Ocean and predicting its evolution in response to increasing atmospheric CO2. The research methodology will combine collection of historical and new field data, laboratory process-level studies and numerical work in order to improve our understanding of the mechanisms controlling the production of bloom-forming phytoplankton groups, their sinking rate and biodegradation when exported to the intermediate and deep waters (100-1000 m).

Objectives
The general objective is to develop an ocean - sea-ice - biogeochemical model for the Southern Ocean south of 30°S, in order to budget the present-day CO2 uptake and predict the ocean's response to doubled atmospheric CO2, scheduled for the second-half of 21st century.

Specific objectives are: (1) The set-up of in-vitro process studies to achieve a mechanistic understanding of (i) the different factors that control growth, sedimentation of Antarctic phytoplankton and its bacterial breakdown and (ii) the potential proxies of these processes; (2) To complete existing data-bases for carbon fluxes; (3) To develop a realistic ocean - sea-ice - biogeochemical model for the region south of 30°S; (4) To simulate the situation at doubled atmospheric CO2.

Methodology and interaction between partners
1. In-vitro experiments with phytoplankton cultures (ULB-VUB-MRAC) to study the factors controlling (i) growth, sedimentation and decay of phytoplankton (diatoms and Phaeocystis) under saturating and non saturationg conditions of light, iron and Si (ULB) and (ii) new production (VUB) and the expression of proxy signals such as Ba, barite (VUB, MRAC), ?15N (VUB), ?30Si (MRAC).

2. Composing a data base for carbon fluxes (ULg-VUB-MRAC)
pCO2 (ULg): (1) Collection of data for under-sampled regions and seasons; (2) Construction of an autonomous pCO2 analysis system for use on board supply ships; (3) Elaboration of algorithms for the reconstruction of pCO2 distribution fields based on satellite observation (SEAWIFS) of SST and Chl a. (4) Deduce atmosphere-ocean CO2 fluxes using ERS wind speed data and pCO2 distribution fields.

Carbon export and mineralization flux (VUB - MRAC): Estimation of the carbon export flux and the POC mineralization profile in the mesopelagic water column (100-1000m) using proxies (new production, f-ratio; 234Th-deficit; ?30Si of biogenic silica; ?15N of suspended organic matter; Ba-barite). These export fluxes are compared with POC and proxy fluxes in sediment traps, sediments and with model results.

Optimization of the Ba-barite proxy (VUB-MRAC): (1) The co-variation of mesopelagic Ba and POC export is verified; (2) Identification of the different factors that control the Ba-signal; (3) Comparison of export production based on mesopelagic Ba with export production based on POC flux in sediment traps; (4) Reconstruction of the POC mineralization flux and mineralization profile for the mesopelagic water column; (5) Optimization of existing algorithms relating the mesopelagic Ba signal to export production and develop new ones.

3. Numerical experimentation: Construction of a Ocean-Ice-Biogeochemical model (ULB-UCL)
Coupling of a biogeochemical model (SWAMCO) to a 3D ocean - sea-ice model: (1) Optimization of the 3D ocean - sea-ice model; simulations for the modern ocean (1988-2000) and for the future ocean under doubled atmospheric CO2 (UCL); (2) Aggregation and optimization of the existing 1D biogeochemical SWAMCO model (ULB); (3) Elaboration of an integrated oceaan - sea-ice - biogeochemical model (UCL-ULB).
The validated integrated model is used for the estimation of the CO2 mass balance on global, regional and seasonal scales. Sink and source regions are identified as is the sequestration of organic carbon in the deep sea. The model is used to simulate the situation at atmospheric CO2 x 2.

Expected results
A better evaluation of the role of the Southern ocean in Global Change. This will be achieved as a result of the development and improvement of complementary proxy approaches contributing to the understanding of the biological carbon pump functioning in an iron-limited Southern Ocean. Simulation of the Southern Ocean's carbon pump functioning at CO2 x 2.

Partners

Vrije Universiteit Brussel - ANCH: Has expertise for (i) the determination of new production based on 15N isotope dilution methods and the modelling of nitrogen fluxes related with uptake and release; (ii) the application of proxies of new production and export production (Ba-barite; 234Th-deficit; ?15N).

Université Libre de Bruxelles - ESA: Has expertise in the field of phytoplankton processes (growth, sedimentation, grazing, bacterial breakdown) and the development of biogeochemical models.

Musée Royal d'Afrique Centrale - Koninklijk Museum voor Centraal Afrika: Has expertise in the field of trace element and isotope proxy analysis and interpretation.

Katholieke Universiteit Leuven - ASTR: Has expertise with hydrodynamic modeling coupled ocean - sea-ice models.

Université de Liège - GHER: Has expertise in the field of ocean - atmosphere CO2 exchange and physico-chemistry of oceanic inorganic carbon.

Coordinates
Dehairs Frank, Co-ordinator: Vrije Universiteit Brussel, Analytische Chemie, ANCH, Pleinlaan 2, B-1050 Brussel; Tel: 32-2-629.32.60; Fax: 32-2-629.32.74; e-mail: fdehairs@vub.ac.be
Lancelot Christiane: Université Libre de Bruxelles, Ecologie des Systèmes Aquatiques (ESA), Campus de la Plaine, CP 221, Boulevard du Triomphe, B-1050 Bruxelles; Tel: 32-2-650.59.88; Fax: 32-2-650.59.93; e-mail: Lancelot@ulb.ac.be
André Luc: Musée Royal d'Afrique Centrale - Koninklijk Museum voor Centraal Afrika; Mineralogy, Petrography and Geochemistry, Leuvensesteenweg 13, B-3080 Tervuren; Tel: 32-2-769.54.59; Fax: 32-2-759.54.32; e-mail: landre@africamuseum.be
Deleersnijder Eric: Université Catholique de Louvain, Institut d'Astronomie et de Géophysique Georges Lemaïtre (ASTR), Chemin du Cyclotron 2, B-1348 Louvain-la Neuve; Tel: 32-10-47.32.97; Fax: 32-10-47.47.22; e-mail: ericd@astr.ucl.ac.be
Frankignoulle Michel: Université de Liège, Unité d'Océanographie Chimique, Geohydrodynamics and Environmental research (GHER), Institut de Physique, batiment B5, B-4000 Sart-Tilman; Tel: 32-4-366.33.26; Fax: 32-4-366.23.55; e-mail: Michel.Frankignoulle@ulg.ac.be

The Users Committee

The Users Committee is composed of scientists active in Southern Ocean research that is complementary to the expertise developed within the present network, and who are participating and/or steering international organisations concerned with Global Change.

Composition of the committee
Tison Jean-Louis; Université Libre de Bruxelles, Département des Sciences de la Terre et de l'Environnement, Unité de Glaciologie, Brussels, Belgium
De Baar Hein J.W., Nederlands Instituut voor Onderzoek der Zee (NIOZ), Den Burg, The Netherlands
Aumont Olivier, Laboratoire d'Océanographie Dynamique et de Climatologie (LODYC), Institut Pierre et Simon Laplace, Paris, France
Vanderborght Oscar, Institute of Environmental Sciences, Universiteit Antwerpen & National Committee IGBP-Global Change, Belgium
Trull Thomas W., Antarctic Cooperative Research Centre, University of Tasmania, Hobart, Tasmania, Australia