KEOPS 2 (Kerguelen Ocean and Plateau compared Study 2) is a project funded by Agence Nationale de la Recherche (ANR), Centre National de la Recherche Scientifique  / Institut National des Sciences de l'Univers (CNRS/INSU) and Institut Polaire Paul-Emile Victor (IPEV).

KEOPS 2 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 (KEOPS 1, January to February 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 KEOPS 1 have also given rise to new puzzling questions that are focus of this new project.

During KEOPS 1, 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. KEOPS 2 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 approaches based on molecular biology techniques are also used to address the question whether different species and organisms compete and/or collaborate for iron acquisition. Observations from KEOPS 1 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.

KEOPS 2 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 are a central issue of KEOPS 2. 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. KEOPS 2 will revisit the Kerguelen bloom during its onset, which will complement the picture obtained during the third month of the phytoplankton bloom (KEOPS 1).

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 KEOPS 2 will allow to determine the mixed layer depth in early spring and to study the biological response to varying physical forcing inside and outside mesoscale structures. To address these different questions, the KEOPS 2 community will apply a suite of novel techniques and strategies. The re-investigation of the natural laboratory off Kerguelen Island clearly offers an excellent opportunity to significantly advance our understanding on how natural iron fertilization affects biogeochemistry in the Southern Ocean.