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Karine Leblanc

DR2 CNRS section 19
88 %
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Présentation

My main research interest is the study of a siliceous phytoplankton group called diatoms as well as the silicon cycling in surface waters. Diatoms are an essential component of marine algae and are known to sediment rapidly out of the surface layer to the deep ocean, where parts of the carbon and other elements constituting their biomass can be sequestered. For this reason, diatoms are a key players in the CO2 exchange between the ocean and the atmosphere and determining the environmental conditions leading to their dominance or decline has global significance on marine foodwebs as well as on climate feedbacks.

I’m mainly interested in characterizing how major nutrients availability limit diatom growth and control the shift between diatoms and other major phytoplanktonic groups in diverse oceanic systems, as well as how this affects the biological pump leading to export production.

During my post-doc at the College of Marine Studies in Lewes (USA) I became interested in the role of trace metals such as iron and zinc on diatoms growth and on their elemental stoichiometry. This allowed me to participate to cruises in the sub-arctic and the sub-antarctic Pacific to investigate the impact of trace metal additions in HNLC areas (High Nutrient Low Chlorophyll), as well as collaborate on a series of T°, pCO2 controlled chemostat experiments int the Bering Sea and North Atlantic.

I have also worked on the use of a fluorescent silicification probe (PDMPO) in order to identify within a mixed natural plankton community which species are the key players regarding Si uptake and to quantify their relative contribution to Si production. A routine protocol developped on an image analysis software coupled to epifluorescence microscopy now allows to quantify for each diatom cell (and hence species) the relative amount of PDMPO fluorescence which is proportional to Si production.

I now continue my research at CNRS in Marseille (Luminy) where I continue to study diatom community structure, and how diversity, life strategies but also mortality modes may alter the efficiency of the biological pump. I have participated to several programs in oligotrophic regions of the Mediterranean Sea and the South Pacific, where diatoms are not necessarily dominant but have a specific ability to live in close associations with diazotrophic cyanobacteria. I am interested in using single-cell activity markers (viability, lipid, silicification) to better understand species-specific differences in elemental stoichiometry and physiological rates. I particularly enjoy field work and oceanographical cruises, notably in the Southern Ocean, where diatom communities are key components of the planktonic ecosystems.

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