Interactions between the microbial network and the organic matter in the Southern Ocean: impacts on the biological carbon pump

• Main Author: Dumont, Isabelle
• Other Authors: Becquevort, Sylvie, Lancelot, Christiane, Schoemann, Véronique, Tison, Jean-Louis, Gillan, David, Dehairs, Frank, Chou, Lei, Servais, Pierre
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: Universite Libre de Bruxelles 2009
• Subjects: Agronomie générale; Sciences exactes et naturelles; Carbon cycle (Biogeochemistry) > Antarctic Ocean; Biogeochemistry > Antarctic Ocean; Sea ice > Antarctic Ocean; Marine plankton > Antarctic Ocean; Saccharides; Cycle du carbone (Biogéochimie) > Austral; Océan; Biogéochimie > Austral; Glace de mer > Austral; Plancton marin > Austral; TEP/glace de mer antarctique; POC; TEP; DOC; Antarctic sea ice; Antarctic; Southern Ocean; Weddell Sea; Austral; Bellingshausen Sea; Pacific; Weddell; Antarctic Ocean; Antarc*; Antarctique*; ice algae; Sea ice
• Online Access: http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/210300; https://dipot.ulb.ac.be/dspace/bitstream/2013/210300/1/7e2de6f3-b588-4f18-8f19-a8bf78d76fbf.txt; https://dipot.ulb.ac.be/dspace/bitstream/2013/210300/4/cde05a14-6a44-4f5f-923d-70cfd5cdb967.txt

The Southern Ocean (ca. 20% of the world ocean surface) is a key place for the regulation of Earth climate thanks to its capacity to absorb atmospheric carbon dioxide (CO2) by physico-chemical and biological mechanisms. The biological carbon pump is a major pathway of absorption of CO2 through which the CO2 incorporated into autotrophic microorganisms in surface waters is transferred to deep waters. This process is influenced by the extent of the primary production and by the intensity of the remineralization of organic matter along the water column. So, the annual cycle of sea ice, through its in situ production and remineralization processes but also, through the release of microorganisms, organic and inorganic nutrients (in particular iron)into the ocean has an impact on the carbon cycle of the Southern Ocean, notably by promoting the initiation of phytoplanktonic blooms at time of ice melting. The present work focussed on the distribution of organic matter (OM) and its interactions with the microbial network (algae, bacteria and protozoa) in sea ice and ocean, with a special attention to the factors which regulate the biological carbon pump of the Southern Ocean. This thesis gathers data collected from a) late winter to summer in the Western Pacific sector, Western Weddell Sea and Bellingshausen Sea during three sea ice cruises ARISE, ISPOL-drifting station and SIMBA-drifting station and b) summer in the Sub-Antarctic and Polar Front Zone during the oceanographic cruise SAZ-Sense. The sea ice covers were typical of first-year pack ice with thickness ranging between 0.3 and 1.2 m, and composed of granular and columnar ice. Sea ice temperature ranging between -8.9°C and -0.4°C, brines volume ranging between 2.9 to 28.2% and brines salinity from 10 to >100 were observed. These extreme physicochemical factors experienced by the microorganisms trapped into the semi-solid sea ice matrix therefore constitute an extreme change as compared to the open ocean. Sea ice algae were mainly composed of diatoms but ...