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BELCANTO 2 project

Antarctica phase V (2000-2005)

BELCANTO 2 - Assessing the sensitivity of the Southern Ocean’s biological pump to climate change

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 potential of the SO to further enhance CO2 uptake via the biological pump. However, in the High Nutrient Low Chlorophyll waters of the modern Southern Ocean this does not occur because biological production is iron limited. Future climate-driven changes in water circulation, eolian transport of continental dust, sea ice extent and lithogenic matter input from Antarctic continent, shelf and slope areas will modify the natural
fertilisation patterns of the Southern Ocean. This together with changes in stratification of the upper ocean will impact on ecosystem structure and function, export production and air-sea CO2 flux, with a feedback to climate.

Project description

This project 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 modellers. 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 a 3-D ocean – seaice – 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 the 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 databases 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 the different 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 saturating 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 database for carbon fluxes (ULg-VUBMRAC) 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 mineralisation flux (VUB – MRAC): Estimation of the carbon export flux and the POC mineralisation profile in the mesopelagic water column (100-1000m) using proxies (new production, fratio; 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. Optimisation 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 mineralisation flux and mineralisation profile for the mesopelagic water column; (5) Optimisation of existing algorithms relating the mesopelagic Ba signal to export production and develop new ones.
3 Numerical experimentation: Construction of a 3-D Ocean-Ice-Biogeochemical model (ULB-UCL) Coupling of a biogeochemical model (SWAMCO) to a 3-D ocean - sea-ice model: (1) Optimisation of the 3-D ocean – sea-ice model; simulations for the modern
ocean (1988-2000) and for the future ocean under doubled atmospheric CO2 (UCL); (2) Aggregation and optimisation of the existing 1-D biogeochemical SWAMCO model (ULB); (3) Elaboration of an integrated ocean – sea-ice – biogeochemical model (UCLULB).
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 redoubling.

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 redoubling.

Complementary resources about this scientific project

Partners

VUB-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; 234Thdeficit;
15N).
ULB-ESA Has expertise in the field of phytoplankton processes (growth, sedimentation, grazing, bacterial breakdown) and the development of biogeochemical models.
MRAC-KMMA Has expertise in the field of trace element and isotope proxy analysis and interpretation.
UCL-ASTR Has expertise with hydrodynamic modelling coupled ocean – sea-ice models.
ULg-GHER Has expertise in the field of ocean – atmosphere CO2 exchange and physicochemistry of oceanic inorganic carbon.
ACE-CRC & CSIRO
Royal Netherlands Institute for Sea Research

Contact information

Coordinator: Frank Dehairs
Vrije Universiteit Brussel (VUB)
Departement Analytische Chemie (ANCH)
Pleinlaan 2
B-1050 Brussels
Tel: +32 (0)2 629 32 60
Fax: +32 (0)2 629 32 74
fdehairs@vub.ac.be
www.vub.ac.be/infovoor/onderzoekers/research/
team.php?team_code=ANCH

Partner 2: Christiane Lancelot
Université Libre de Bruxelles (ULB)
Ecologie des Systèmes Aquatiques (ESA)
Campus de la Plaine
CP 221
Boulevard du Triomphe
B-1050 Brussels
Tel: +32 (0)2 650 59 88
Fax: +32 (0)2 650 59 93
Lancelot@ulb.ac.be
www.ulb.ac.be/rech/inventaire/unites/ULB115.html

Partner 3: Luc André
Musée royal de l’Afrique Centrale (MRAC-KMMA)
Section de Minéralogie et Pétrographie
Leuvensesteenweg 13
B-3080 Tervuren
Tel: +32 (0)2 769 54 59
Fax: +32 (0)2 759 54 32
landre@africamuseum.be
www.africamuseum.be/research/projects/prj_detail?prjid=395

Partner 4: Hugues Goosse
Université Catholique de Louvain (UCL)
Institut d’Astronomie et de Géophysique Georges Lemaître (ASTR)
2, chemin du Cyclotron
B-1348 Louvain-la Neuve
Tel: +32 (0)10 47 32 98
Fax: +32 (0)10 47 47 22
hgs@astr.ucl.ac.be
www.astr.ucl.ac.be

Partner 5: Alberto Borges
Université de Liège (ULg)
Unité d’Océanographie Chimique
Geohydrodynamics and Environmental research (GHER)
Institut de Physique, Bat. B5
17, allée du 6 août
Sart Tilman
B-4000 Liège 1
Tel: +32 (0)4 366 31 87
Fax: +32 (0)4 366 23 55
Alberto.Borges@ulg.ac.be
www.ulg.ac.be/cms/c_609864/en/chemical-oceanography

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