Observing physical-biological coupling at the submesoscale thanks to innovative methodologies for sampling in situ at high resolution. The scientific objectives of the project OSCAHR (Observing Submesoscale Coupling At High Resolution) are to characterize a submesoscale structure and to study its influence on the distribution of biogenic elements and the structure and dynamics of the first trophic levels associated with it. The strategy is based on an adaptive satellite-based approach and on the use of very recent or new instruments allowing to sample the surface layer at high spatial and temporal frequency. The original set of multidisciplinary data will allow to validate measurements from remote sensing (radar altimetry, ocean color, reconstitution of planktonic assemblages) in coastal areas. ----- Les objectifs scientifiques du projet OSCAHR (Observing Submescale Coupling At High Resolution) sont de caractériser une structure dynamique de sous-mesoéchelle et d'étudier son influence sur la distribution des éléments biogènes et sur la structure et la dynamique des premiers niveaux trophiques qui lui sont associés. Notre méthodologie comprend l'utilisation de nouvelles plateformes d'observation pour l'échantillonnage de la couche superficielle de l'océan à une fréquence spatiale et temporelle élevée. En particulier, un MVP (Moving Vessel Profiler) est déployé avec des capteurs CTD, Fluorescence et LOPC (Laser Optical Particle Counter) et une nouvelle version du cytomètre automatisé en flux est installée pour l'échantillonnage en temps réel et à haut débit des groupes fonctionnels phytoplanctoniques, du microphytoplancton aux tocyanobactéries (dont le Prochlorococcus). Deux sources d'eau de mer ont été utilisées dans l'OSCAHR : en plus de la prise d'eau de surface à bord, un nouveau système de pompage est développé et testé afin d'échantillonner la colonne d'eau supérieure à une résolution d'un mètre.

What drives phytoplankton diversity at fine scales? Phytoplankton diversity is a key component in ocean biogeochemical services and contributes to the resilience and health of ocean ecosystems in respect to local and global stressors, including climate change. Understanding the mechanisms behind phytoplankton diversity in the open ocean is a matter of concern, especially in these years in which large Marine Protected Areas are created in international waters and an international legally binding treaty on Marine Biodiversity Beyond National Jurisdiction is under negotiation. Model studies suggest that finescale ocean dynamics are an important driver of plankton diversity and several scenarios have been suggested. In situ observations however are difficult to perform, due to the ephemeral nature of finescale features and the difficulty of tracking them from available remote sensing. This observational limit will be largely reduced by the SWOT mission, in particular during the fast sampling phase, opening new possibilities to biophysical experiments in the open ocean. The BIOSWOT-Med campaign aims at exploiting SWOT observations for unveiling the drivers of phytoplankton diversity in the Western Mediterranean. The western Mediterranean Sea is characterized by high plankton diversity, low nutrient concentration, and weak oceanic circulation. Here, finescale features, even if weak and short-lived, can strongly modulate the microbial community structure. To study the finescale biophysical coupling, and its impact of phytoplankton diversity, the BIOSWOT-Med campaign will follow the temporal evolution of eddies and filaments over the western Mediterranean SWOT crossover. The physical-biochemical coupling at the frontal zone between Atlantic Water recently entered in the Mediterranean basin and modified Atlantic Water coming from cyclonic circulation in the western Mediterranean basin will be studied through an adaptive Lagrangian sampling strategy using the software SPASSO (Software Package for an Adaptive Satellite-based Sampling for Oceanographic cruises) developed in previous research cruises. This physical information will be paired by a multi-sensor characterization of the planktonic community, including advanced molecular (meta-transcriptomics, metagenomics and meta-barcoding) techniques, and the use of autonomous and robotic platforms. Institutes involved in the campaign: AMU, LOCEAN, CEA, CNR, CNRS, CSIC, Fisheries and Ocean Canada, IFREMER, IRD, MBARI, NWRA, OGS, SHOM, Sorbonne Université, SZN, UCSD, ULCO, University of Exeter, University of Washington.

The LAgrangian Transport EXperiment (LATEX) project (2008-2011) is designed to study the mechanisms of formation of anticyclonic eddies and their influence on cross-shelf exchanges in the western part of the GoL. The dynamics of mesoscale eddies is particularly important in this part of the GoL since it represents a key region for regulating the outflow from the continental shelf. The eddy dynamics is investigated using Symphonie, a 3-dimensional, primitive equation model, with a free sea surface, hybrid sigma coordinates, based on Boussinesq and hydrostatic approximations [Marsaleix et al., 2006, 2008]. We use the upwind-type advection-diffusion scheme adapted by Hu et al. [2009] to improve the ability of the model to reproduce coastal mesoscale eddies in the western part of the GoL. In the present study, the model is implemented over the whole GoL with an horizontal resolution of 1 km × 1 km (Figure 1). The vertical discretization consists of 40-hybrid vertical levels. The vertical resolution varies from 1 m in the upper ocean to 40 m near the bottom. "For a complete review of the LATEX projet, see : - Petrenko, A., A., Doglioli, A.M., Nencioli, F., Kersalé, M., Hu, Z., d'Ovidio, F. (2017). A review of the LATEX project: mesoscale to submesoscale processes in a coastal environment. Ocean Dynam., 67:513 - doi: 10.1007/s10236-017-1040-9 - https://doi.org/10.1007/s10236-017-1040-9 ----- Le projet LAgrangian Transport EXperiment (LATEX) (2008-2011) est conçu pour étudier les mécanismes de formation des tourbillons anticycloniques et leur influence sur les échanges entre plateaux dans la partie occidentale du GdL. La dynamique des tourbillons à méso-échelle est particulièrement importante dans cette partie du GdL, car elle représente une région clé pour la régulation du flux sortant du plateau continental. La dynamique des tourbillons est étudiée à l'aide de Symphonie, un modèle d'équation primitive tridimensionnel, avec une surface de mer libre, des coordonnées sigma hybrides, basé sur Boussinesq et des approximations hydrostatiques [Marsaleix et al., 2006, 2008]. Nous utilisons le schéma d'advection-diffusion de type vent debout adapté par Hu et al [2009] pour améliorer la capacité du modèle à reproduire les tourbillons côtiers à méso-échelle dans la partie occidentale du GdL. Dans la présente étude, le modèle est mis en œuvre sur l'ensemble du GdL avec une résolution horizontale de 1 km × 1 km (Figure 1). La discrétisation verticale est constituée de 40 niveaux verticaux hybrides. La résolution verticale varie de 1 m dans la partie supérieure de l'océan à 40 m près du fond. Pour plus d'information sur le projet LATEX : - Petrenko, A., A., Doglioli, A.M., Nencioli, F., Kersalé, M., Hu, Z., d'Ovidio, F. (2017). A review of the LATEX project: mesoscale to submesoscale processes in a coastal environment. Ocean Dynam., 67:513 - doi:10.1007/s10236-017-1040-9 - https://doi.org/10.1007/s10236-017-1040-9