The waltz of phytoplankton in the Mediterranean

the impact of fine-scale currents on phytoplankton communities.

In 2018, during the PROTEVSMED-SWOT campaign that took place south of the Balearic Islands, an international consortium, taking advantage of near real-time satellite information, implemented a sampling strategy to traverse a frontal zone separating different water masses. In situ multi-parameter sensors mounted on the ship, on a towed fish and on an ocean glider were used to sample physical and biogeochemical variables at high spatial resolution. Special attention was paid to tailoring the sampling route to also estimate vertical velocities in the frontal zone. This strategy provided a general view of an oceanic zone characterized by the presence of a narrow front with an associated vertical circulation.

A multiparametric statistical analysis of the collected data identified two water masses characterized by different abundances of nine phytoplankton cytometric functional groups, as well as by different chlorophyll a and O2 contents. Our study shows that lagrangian fronts induced by fine-scale circulation, although much weaker than intense current fronts, maintain a strong structuring effect on the phytoplankton community by separating different taxa at the surface.

The methodology and results of the PROTEVSMED-SWOT campaign form a solid basis for the future BIOSWOT campaign planned in the same area in 2023, a few months after the launch of the SWOT altimetry satellite. This new altimetry satellite, equipped with a Ka-band bistatic SAR system, will provide very high resolution sea surface height measurements, very useful for fine scale studies.

Source:

Tzortzis, R., Doglioli, A. M., Barrillon, S., Petrenko, A. A., d'Ovidio, F., Izard, L., Thyssen, M., Pascual, A., Barceló-Llull, B., Cyr, F., Tedetti, M., Bhairy, N., Garreau, P., Dumas, F., and Gregori, G.: Impact of moderate energetic fine-scale dynamics on the phytoplankton community structure in the western Mediterranean Sea, Biogeosciences, https://doi.org/10.5194/bg-2021-38, accepted, 2021.  

Acknowledgments :

This work was supported by CNES within the BIOSWOT-AdAC project (https://www.swot-adac.org) and by the MIO Transversal Axes program (AT-COUPLAGE).

The authors acknowledge that the Délégation Générale de l'Armement (DGA) funded the campaign reported here through the Protevs and Protevs II upstream study programs. They thank the technical team of the Service Hydrologique et Océanographique de la Marine (SHOM) and the crew of the ship Beautemps-Beaupré.

Contacts :

Roxane Tzortzis (roxane.tzortzis@mio.osupytheas.fr)

Andrea Doglioli (andrea.doglioli@mio.osupytheas.fr)

Gérald Gregori (gerald.gregori@mio.osupytheas.fr)

Francesco d’Ovidio (francesco.dovidio@locean.ipsl.fr