Size-fractionated carboxylase activities during a 32 h cycle at 30 m depth in the Northwestern Mediterranean Sea after an episodic wind event

Using size fractionation filtration (1 mum), we associated carboxylase activities (Rubisco, beta -carboxylases) and chlorophyll measurements with cell enumeration by flow cytometry at a permanent site of the central Ligurian,Sea in the north-western Mediterranean Sea (73 degrees 25 'N-7 degrees 51 'E). The analyses were carried out over a day/night Cycle (at 30 m depth) following a strong wind event, during the transition period from spring mesotrophic to summer oligotrophic conditions. The highest values of Rubisco activity and beta -carboxylase activity per chlorophyll a (Chl a) for >1 mum cells were observed during the light period of the cycle, reaching 18.9 and 4.3 nmol CO2 (mug Chl a)(-1) h(-1), respectively. This higher activity is assumed to be correlated with a dominance of nanoflagellates in the phytoplankton community. Such phytoplankton species generally had higher beta -carboxylase activity, expressed as a percentage of Rubisco activity (the betaC/R ratio), than diatoms. Using ooze, cytometry analysis to enumerate those cells