Between March 18th - 20th an unexpected increase in microphytoplankton cells was detected at OBSEA. The CytoSub, an underwater flow cytometer instrument, detected a peak of 20 000 cells/L, mainly composed of diatoms - single celled ocean, freshwater or soil colonies-forming organisms. This number is a whopping 20 times the density in comparison to the same metric in the morning of March 18th. By March 21st, concentrations had returned to previous levels. This observation is credited to the hourly sampling strategy that is being employed.

Data analysis by MIO

Many direct and indirect causes for such an increase in cell concentration are possible culprits. This particular bloom of phytoplankton is hypothesised to be due to currents, generated by easterly winds.

Images of the phenomenon were generated as a result of the collaborative work between OBSEA (where the instrument is installed), CytoBuoy (makers of the CytoSub), and the LOV laboratory (Sorbonne Université/CNRS, plankton imaging experts) under the ANERIS project.

Cell images by the CytoSub

The imaging protocol used for the capturing of the event was set up and optimised by collaborators from MIO Marseille (AMU/CNRS), Clémentine Gallot and Melilotus Thyssen, who analysed the data as well. 

More about the CytoSub deployment you can read here: https://aneris.eu/news/cytosub-deployed-obsea-cabled-observatory