KEOPS 2

The project KEOPS2 (Kerguelen Ocean and Plateau compared Study) is the second French initiative to investigate the impact of natural iron fertilization on the biogeochemical cycles in the Southern Ocean. One of the first natural iron fertilization experiments (KEOPS1, Jan.to Feb. 2005) has provided key findings on how the ecosystem functioning and the biogeochemical cycling of elements are affected by natural iron fertilization, but the observations made during KEOPS1 have also given rise to new puzzling questions that will be focus of this project. During KEOPS1, the mechanism of natural iron fertilization was clearly demonstrated, however, the supply of iron from below was not sufficient to meet the biological iron demand in surface waters. We will undertake a comprehensive study of the sources of new and regenerated iron and the biotic and abiotic processes that render different forms of iron, such as organic or lithogenic particulate iron bioavailable to microorganisms. Novel biomolecular-based approaches will be used to address the question whether different species and organisms compete and/or collaborate for iron acquisition. Observations from KEOPS1 strongly suggest a decoupling between the major elemental cycles in the naturally fertilized region. To better constrain the efficiency of fertilization in terms of CO2 uptake it is of critical importance to understand this observation. We will put emphasis on determining the affinities of phytoplankton for different new or regenerated nutrients, on elemental uptake ratios and whether processes such as nitrification and ammonium regeneration in surface waters are of importance in sustaining phytoplankton primary production. The processes that determine carbon export to depth will be a central issue of KEOPS2. What part of the primary production is remineralized in surface and mesopelagic waters, and what organisms are responsible for the organic matter transformations? Our aim is to link the investigation of these processes to the diversity of the plankton community (from viruses to zooplankton) and to their function in the carbon cycle. KEOPS2 will offer us the opportunity to revisit the Kerguelen bloom during its onset, which will complement the picture we obtained during the third month of the phytoplankton bloom (KEOPS1). Insights on what processes govern carbon export will also be gained from the detailed analyses of material collected in sediment traps deployed during different bloom stages and depths. A major challenge will be to establish a seasonal budget of different chemical elements that will require a proper description of the variability of the mixed layer depth. The novel strategy adapted by KEOPS2 will allow us to determine the mixed layer depth in early spring and to study the biological response to varying physical forcing inside and outside mesoscale structures. The re-investigation of the natural laboratory off Kerguelen Island clearly offers an excellent opportunity to confirm our expertise and to significantly advance our understanding on how natural iron fertilization affects biogeochemistry in the Southern Ocean. To address these different questions, the KEOPS2 community will conduct a cruise in the Southern Ocean in late 2011. During this cruise a suite of novel stategies and innovatives techniques, in physics, geochemistry, biology will be applied. The achievement of the objectives above required a pluridisciplinary expertise. This will be provided by 90 participants coming from 11 french and 10 foreign laboratories ((Australia, Chilli, Greece, Italia, New Zealand, Russia, and USA). The KEOPS2-ANR project is a contribution to the global project. 4 French laboratories are the partners of the KEOPS2-ANR. They have been major participants to KEOPS1 and their expertises in iron biogeochemistry, geochemistry of tracers and interaction between biogeochemical cycles and plankton (from bacteria to marcozooplankton) are worldwide recognised.