Understanding the role of finescales in the interactions of ocean dynamics and biogeochemistry in coastal zones in the NW Mediterranean Sea
In coastal environments, mesoscale and sub-mesoscale structures are important drivers of exchanges with the open ocean and of biogeochemical processes. A cyclonic circulation, often called the Northern Gyre, occupies the Liguro-Provençal-Catalan basin. In addition to the seasonal variability of the dynamics, there are mesoscale and sub-mesoscale dynamics which drive the biological activity. Fine scales are more than just disturbances around a mean circulation. They are even known to contribute to the organization, conservation and redistribution of water masses, and therefore influence the availability of nutrients in the euphotic zone, where photosynthesis occurs.
While mesoscale and sub-mesoscale processes are the subject of much numerical and conceptual studies, until recently their in-situ observation remained a challenge because they are small, moving, and short-lived.
The objective of the C-SWOT-2023 campaign was to unravel the interaction between ocean dynamics and biochemistry in north-western Mediterranean basin, including the North Current, its variable large and small scale dynamics, as well as observations of high resolution oceanic fields including biogeochemistry. For that, mesoscale structures edges were investigated at the beginning of spring when the fronts are the deepest and the most likely to give birth to instabilities associated with significant vertical velocities, which in turn may fuel the euphotic layer.
To carry out the field experiment, a rarely deployed sampling strategy was used. During the C-SWOT-2023 campaign two research vessels sailed along together to explore statistics of the surface ocean dynamics (vorticity, strain, divergence) that are seldomly accessible in fine scale observations. In situ observations included the use of the Seasoars equipped with SUNA and CTD sensors. The campaign also investigated how precise the SWOT altimetric data are along and across its swaths and provided information regarding what part of the dynamics can be directly observed and commensurable with the one derived from the altimetric data and the geostrophic balance assumption. AIS-derived currents from ships in the sampling area during the C-SWOT-2023 campaign were used to cross-validate SWOT derived currents.
High resolution modeling with a resolution of a few hundred meters were used to anticipate the field experiment with the two ships sailing in parallel tracks and were used to support data analysis. It included the use of the SWOT Simulator for Ocean Science and outputs of the ocean model Mars3D Mediterranée.
Focusing on the low trophic levels (nutrients and phytoplankton) of the marine food web, the C-SWOT-2023 campaign tried to highlight where and when “physics is brought to life” in the NW Mediterranean Sea.
Principal investigators: Franck Dumas (franck.dumas@shom.fr) (Shom); Pierre Garreau (pierre.garreau@ifremer.fr) (IFREMER).
Contact point for the study site: Franck Dumas (franck.dumas@shom.fr).
Checkout the C-SWOT-2023 blog!