There is now over a ten year experience in investigating the space time distribution of oceanic phytoplankton at high frequency and at the single cell level. This was a prerequisite to have access to the dynamics of phytoplankton at the time scale of its variability and shed a new light on the functioning of phytoplankton microbial assemblages.

Our group designed a new instrument in collaboration with an EU company to extend this approach to heterotrophic microorganisms. A prototype is under validation and the first applications should be run this year. As a laboratory instrument, it can only be run on pumped water. The real challenge, is to make this instrument submersible to be able to explore the water column at least down to 2500 m depth.

In the epipelagic layer, this technology coupled to that developed for phytoplankton and already submersible, would open access to the dynamics of both autotrophic and heterotrophic microorganisms and to their interactions.

In the mesopelagic layer and below, we know that the biological activity is as important as the one in the epipelagic layer but remained almost out of reach because of its dilution with depth and of the lack of tools to assess it.

Making submersible the new technology for heterotrophic microorganisms will be a real breakthrough enabling to better quantify the functioning of the biological carbon pump and reduce uncertainties of large scale models in the frame of global changes. It will also provide a unique instrument to include this biological information into ocean global observing systems in an automated way and at a frequency compatible with that of physico-chemical sensors.