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Talk of Dr Jeffrey W. Krause

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Thursday, October 1st, 2015 at 13h00

Labex OT-Med and MIO (Mediterranean Institute of Oceanography) have a pleasure to invite you for a talk by

Dr Jeffrey W. Krause
Senior Marine Scientist, Dauphin Island Sea Lab (Dauphin Island, Alabama, United States)
Assistant Professor, University of South Alabama (Mobile, Alabama, United States).

This talk is entitled :
"Laboratory and Field Assessment of Silicon uptake and Accumulation in Picocyanobacteria"
and will be given on Thursday, October 1st, 2015 at 13 h at OCEANOMED, 163 Av de Luminy, Marseille.


Recently picocyanobacteria from the genusSynechococcus were observed to accumulate elemental Silicon in the eastern equatorial Pacific and Sargasso Sea. While the absolute quantities were low, e.g. amoles Si per cell, the Silicon content normalized to organic matter revealed ratios up to 50% of those for diatoms. Given the high abundance of Synechococcus relative to diatoms, especially in the oligotrophic open ocean, this group may exert a diffuse control on the ocean Si cycle. The factors regulating Si accumulation in Synechococcus in the laboratory and their contribution to total biogenic silica production in the field were explored in a project funded by the United States National Science Foundation. Culture experiments conducted in four separate laboratories confirm the accumulation of significant amounts if Si by six clones of marine Synechococcus. These experiments examined Si quantities and the rate of Si accumulation as a function of dissolved silicic acid concentration, phosphate concentration and growth rate. While many clear patterns emerge, the purpose of Si accumulation inSynechococcus remains a mystery. During field work in the North Atlantic subtropical gyre, the picoplankton size class (cells <3 µm) was observed to contribute a measurable, and at times significant, proportion of biogenic silica standing stock and to its rate of production. These trends were robust after correcting biogenic silica, and the calculated rates which use these data, for interference by lithogenic silica. Our results suggest picoplankton may have a small, but relatively stable, contribution to biogenic silica in this region, which underlies a more dynamic microplankton (cells >3 µm) biogenic silica pool driven by diatoms.