SUMMARY

This research proposal aims to assess to which extent ice-covered polar oceans contribute to processes regulating the Earth's climate. It involves a new multidisciplinary consortium combining the expertise of glaciologists, biologists, geochemists and ecosystems-modelers of the Université Libre de Bruxelles (ULB).

The main goal of the project is to study,understand and quantify the physical and biogeochemical processes associated with the sea ice biota that govern the emissions of marine gases of climatic significance. These processes are indeed presently unknown and therefore not integrated into Oceanic Biogeochemical Climate Models (OBCMs). In this context, particular attention will be paid to Carbon Dioxide (CO2) and Dimethyl Sulphide (DMS), both actively involved in the sea ice microbial metabolism. On a global level, CO2 is well known for its efficient greenhouse gas behavior, while DMS has the recognized potential to stabilize the climate against warming by controlling the incident solar energy via the production of aerosols and cloud condensation nuclei. It has now been demonstrated that iron can play a crucial role in controlling phytoplanktonic productivity and the biological carbon pump in the Southern Ocean. This is, however, yet to be assessed for the Arctic Ocean. The work programme will thus in addition focus especially on the biogeochemical cycle of iron (origin, availability and fate) in the sea ice environment.

The geographical coverage will include, for comparison, both the Arctic and the Antarctic oceans where the mechanisms controlling the carbon production and the relative importance of anthropogenic and marine sulphur compounds in cloud formation processes are quite contrasted.

The research methodology will be highly interdisciplinary and combine field investigations, process-oriented studies both "in situ" and in the laboratory, and modeling work in order to quantify key biological, geochemical and physical interactions between sea ice, the ocean and the atmosphere and to elucidate the controlling mechanisms. Cores collected during field surveys will be used to characterize the distribution of Fe, CO2, DMS and other related physico-chemical and biological parameters in sea ice.Chemical transformation of iron during melting of sea ice and the associated biological and chemical processes will also be studied in the field. Investigations on the mechanisms regulating iron bio-availability and on the iron isotopes bio-signature will be conducted under laboratory-controlled conditions on cultures of polar micro-organisms. Each topic will involve the development of new methodologies including, for example, fluorescent probes, molecular methods (PCR, DGGE), iron isotope analysis (MC-ICP-MS), iron flow injection analysis (Fe-FIA), extraction and gas chromatography for gaseous DMS.

Modeling effort will involve the development of a new sea ice biogeochemical model (SIMCO). Its parameterization will rely on the results obtained during the process studies described above. The online coupling of the SIMCO model with the existing, and currently being improved, model for the upper layer of the Southern Ocean (SWAMCO) should yield an original data set of CO2 and DMS fluxes between the ocean and the atmosphere in polar oceans. These would then be available to ultimately be fed into more general circulation models. The long-standing experience of each partners involved in this project makes it an ideal combination to unravel the complex interplay of physical, chemical and biological processes in evolving sea ice, and to evaluate their potential impact on climatic changes.