The ocean constitutes a large sink for anthropogenic CO2 and thus plays a significant role in the global biogeochemical cycle of carbon and its perturbations. There remain, however, large uncertainties concerning the uptake of anthropogenic carbon by the ocean, mainly due to insufficient knowledge of processes controlling the pCO2 in surface waters.

Most of the previous research efforts have been concentrated on the study of CO2 exchange at the air-sea interface due to temperature effects related to the general circulation of water masses or to the biological activity in terms of new production of organic matter and export to deep waters. The effect of precipitation of calcium carbonate by calcifying organisms in the euphotic zone and the redissolution of their skeletons has presently not been fully taken into account. The precipitation and dissolution processes affect both dissolved inorganic carbon concentration and alkalinity, and plays thus a significant role in the buffering capacity of seawater and its potential to act as a sink or a source of CO2 for the atmosphere. It becomes now evident that one source of the uncertainties for the flux of anthropogenic carbon is related to our poor knowledge of these processes and their quantification, which are fundamental not only for the understanding of the present-day situation but also for the predictive studies in the context of global warming.

The overall objective of this research project is to gain a better knowledge of the oceanic inorganic carbon cycle and its role in climate change. With the combination of field investigations, laboratory experiments and modelling efforts, we aim to study the processes associated with the oceanic production and dissolution of calcium carbonate in order to quantify the role of calcifying phytoplanktonic organisms in sequestering CO2.

Our field studies will be carried out in the area of La Chapelle Bank area (about 47°30'N, 7°30'W) in the Gulf of Biscay. This site has been regularly visited since more than one decade in the framework of Belgian (Global Change) or European (OMEX) research projects, and can be considered as a "time-series" station for which a database of fundamental parameter exist and a good knowledge of the physical processes occurring there has been obtained. In addition, frequent coccolithophore blooms have been observed in the Gulf of Biscay and our measurements of the vertical distribution and fluxes of calcium carbonate indicate a rapid dissolution of the skeletons during settling even in the upper water column over-saturated with respect to CaCO3. This site is thus a suitable location for studying the oceanic inorganic carbon cycle.

Field investigations, supported by remote sensing data, will provide basic, physical, chemical (nutrients, carbon organic and inorganic species), biological (phytoplankton and zooplankton) information. Suspended matter will be collected by continuous centrifugation, in situ filtration of large volumes of water and short-term deployments of sediment traps. In addition, process-oriented studies of the production of organic and inorganic particulate carbon and the dissolution of calcium carbonate will be conducted, using 14C incorporation experiments. The influence of zooplankton grazing and of microbial degradation of organic matter on the dissolution of CaCO3 will be investigated in detail.

Particulate material collected in the Gulf of Biscay will be studied from a physical and chemical point of view using modern microscopic and spectroscopic methods. Different electron microbeam techniques will be used for the characterisation of individual biotic and abiotic suspended particles for their composition, morphology and dissolution features. The calcite surface will be examined by backscattered electrons and by a microprofiler to detect such features, and by "variable-eneragy" electron microprobe analysis to obtain information on the residual organic layer. Particles will also be utilised in laboratory experiments in order to study in detail the dissolution reactions mainly related to the biological activity.
The data acquired during this project will be used to formulate and parameterise the rate equations for the production and dissolution of calcium carbonate. They will also be used for validation purpose and/or input variables of the ocean carbon cycle (OCC) models.

Methodology

The objectives of our study will be achieved by combining field investigations, laboratory experiments and modelling efforts.

Our field of study concerns the area of La Chapelle Bank (about 47°30'N, 7°30'W) in the Gulf of Biscay (Northeast Atlantic Ocean). This site has been regularly visited since more than one decade in the framework of Belgian (Global Change) or European (OMEX) research projects, and a good knowledge of the physical processes occurring in the region has been obtained. In addition, coccolithophorid blooms have been frequently observed in the Gulf of Biscay. Previous measurements of the vertical distribution and fluxes of calcium carbonate (CaCO3) indicate a rapid dissolution of the skeletons during settling even in the upper water column over-saturated with respect to CaCO3. This site is thus a suitable location for studying the oceanic inorganic carbon cycle.

Field investigations, supported by remote sensing data, will provide basic, physical, chemical (nutrients, organic and inorganic carbon species), biological (phytoplankton and zooplankton) information. Suspended matter will be collected by continuous centrifugation, in-situ filtration of large volumes of water and short-term deployments of sediment traps.

Process-oriented studies of the production of organic and inorganic particulate carbon and the dissolution of calcium carbonate will be conducted both in the field and during laboratory assays, using 14C and 45Ca incorporation experiments. The influence of zooplankton grazing and of microbial degradation of organic matter on the dissolution of CaCO3 will be investigated in detail.

Particulate material collected in the Gulf of Biscay will be studied from a physical and chemical point of view using modern microscopic and spectroscopic methods for their composition, morphology and dissolution features.

The data acquired during this project will be used to formulate and to parameterise the rate equations for the production and dissolution of calcium carbonate. They will also be used for validation purposes and/or as input variables of the ocean carbon cycle (OCC) models.


Interaction between the different partners

The co-ordinator, the Laboratory of Chemical Oceanography and Water Geochemistry at the University of Brussels (ULB-LOCGE), is responsible for quantifying the production of organic and inorganic carbon and for studying the dissolution mechanisms of biogenic CaCO3 related to microbial respiration.

The Laboratory of Ecology and Systematics at the Free University of Brussels (VUB-ECOL) will investigate the role of zooplankton grazing in the dissolution of CaCO3.

The Micro and Trace Analysis Centre at the University of Antwerp (UIA-MiTAC) will contribute to the physical and chemical characterisation of suspended matter in relation to the CaCO3 cycle.


Link with International Programmes

The link with existing international programmes will be made via the members of the Users Committee.
- Dr. C. Sabine (University of Washington) is involved in the global estimations of the natural and anthropogenic reservoirs of carbon in the WOCE and JGOFS programmes;
- Dr. R. Francois (Woods Hole Oceanographic Institution) will contribute to a more complete description of the transfer of carbon between the atmosphere and the ocean interior within the framework of his project at WHOI;
- Our project can be linked with the GAIM-IGBP programme via Dr. O. Marchal (Woods Hole Oceanographic Institution) who will simulate CaCO3 fluxes in the global ocean models developed within the framework of the Ocean Carbon-Cycle Model Inter-comparison Project;
- The present research is also linked with the "seatruthing" of remote sensing data collected by SeaWiFS and MODIS through our collaboration with S. Groom (Plymouth Marine Laboratory).


Expected results and/or products

- The mechanisms and rate of individual processes of calcium carbonate production and dissolution will be clarified;
- The integrated production and fate of calcium carbonate in the euphotic zone will be evaluated for the area under investigation;
- The fluxes of organic and inorganic carbon at a larger spatial and temporal scale may be described using coupled 1-D hydrodynamic and biological models.


Partners


Activities

ULB-LOCGE, headed by Prof. L. Chou, has a long standing experience in the study of the biogeochemical processes and their perturbations affecting the cycle of various elements such as carbon, nutrients, major, minor or trace elements either on a local or global scale in the coastal seas and the ocean margins.

VUB-ECOL, headed by Prof. M.-H. Daro, specialises in zooplankton trophodynamics. Its research focuses on the ecological functioning of marine ecosystems with special attention to the first tropic levels (phyto- and zooplankton).

UIA-MiTAC, headed by Prof. R. Van Grieken, has extensive experience in micro- and trace analysis applied to environmental studies. The principal area of research concerns the evaluation of atmospheric deposition of nutrients and heavy metals to the North Sea and the study of aerosols in remote areas and their influence on the global climate.