"Evidence for pulsed exportation in the water column of the northwestern Mediterranean Sea
date: 2016, June 21,
LTO, SCSIO, CAS, Guangzhou,
Directeur de recherche ¨¦m¨¦rite CNRS
Institut M¨¦diterran¨¦en d'Oc¨¦anologie
Universit¨¦ d'Aix Marseille
In the frame of a French oceanographic programme, the vertical distribution of heterotrophic prokaryotes (HP) was investigated in the water column, down to 1100 m, every 3 hours through periods of 36 hours.
HP abundance and viability was directly assessed on board by flow cytometry.In the epipelagic layer, HP were essentially present in the upper 80 m layer. Peaks of HP abundance observed below the 80 m level corresponded to abundance troughs at about 50 m depth in the associated vertical profiles. One permanent peak of HP abundance was observed around 500 m depth, a layer occupied by micro-zooplankton undergoing diel vertical migrations. Deeper peaks of HP abundance were also observed in the mesopelagic realm, and their occurrence was not periodic, in contrast with the initial hypothesis (Denis et al., 2003). These peaks of HP abundance also corresponded to peaks of respiratory activity whose occurrence was initially detected in the late 80s (Savenkof et al., 1993). It is hypothesised that these HP abundance peaks are essentially generated at the surface layer by auto-aggregation and sinking of transparent exopolymer particles (TEP) colonised by HP. The consequences of such a pulsed exportation will be presented and discussed.