Strong hydrodynamic processes observed in the Mediterranean Cassidaigne submarine canyon

IntroductionSubmarine canyons are incisive morphologies that play an important role in the exchange between shallow and deep waters. They interact with the general circulation and induce a specific circulation locally oriented by the morphology. The characteristics of the physical processes at play, the way they interact with each other and the influence of extreme events is still an open question as few observations are available. To answer this question and to improve the representation of submarine canyons in numerical models, it is key to understand the specific circulation patterns and their transitions in these specific environments.MethodsThis paper presents observations of currents, temperature and turbidity along the Cassidaigne canyon, northwestern Mediterranean Sea. Two oceanographic cruises carried out in 2017 and 2019 gathered data from the outer shelf and canyon head at 100-400 m depth to the base of the continental slope at 1900 m depth.Results and DiscussionThe circulation in the Cassidaigne area is subject to upwelling and downwelling-favorable winds, to the Northern Current and its associated mesoscale structures and is oriented by the local morphology. Upwellings occur both during stratified and non-stratified conditions. They are triggered by a wind forcing higher than 14 m s–1 and their consecutive relaxations are marked by a counter-current. Near the canyon head and on the shelf, the current orientation depends on the stratification, the wind, the bottom morphology and the general circulation. The mesoscale variability of the Northern Current can lead to its intrusion over the shelf leading to barotropic cross currents over the canyon. At 1700 m depth, a quasi-permanent residual up-canyon flow is observed in a narrow gorge area and can be extrapolated to the canyon body. Finally, turbidity currents were observed for the first time in connection with upwelling events, suggesting the key role of canyons’ internal hydrodynamics on shelf sedimentary processes

Numerical and experimental modelling of the internal tide near a continental shelf

Les processus de mélange sont essentiels au fond de l'océan car ils permettent la remontée des eaux froides abyssales vers la surface. Une grande question de la communauté océanographique concerne la contribution des ondes internes à ces processus car ces ondes, bien que peu énergétiques en regard des courants marins par exemple, sont présentes partout dans l'océan et y déferlent. Les principales sources d'énergie des ondes internes sont le vent et l'interaction de la marée avec la topographie sous-marine. C'est cette dernière configuration que nous considérons ici, au travers d'expériences de laboratoire et numériques, dans le contexte académique d'un talus continental bidimensionnel dans un océan uniformément stratifié. Nous examinons plus particulièrement le processus de génération du champ d'ondes internes et la structure cinématique de ce champ. Nous discutons également de la manifestation des effets non linéaires lorsque le champ d'ondes se réfléchit au fond de l'océan

Glider-based active acoustic monitoring of currents and turbidity in the coastal zone

The recent integration of Acoustic Doppler Current Profilers (ADCPs) onto underwater gliders changes the way current and sediment dynamics in the coastal zone can be monitored. Their endurance and ability to measure in all weather conditions increases the probability of capturing sporadic meteorological events, such as storms and floods, which are key elements of sediment dynamics. We used a Slocum glider equipped with a CTD (Conductivity, Temperature, Depth), an optical payload, and an RDI 600 kHz phased array ADCP. Two deployments were carried out during two contrasting periods of the year in the Rhone River region of freshwater influence (ROFI). Coastal absolute currents were reconstructed using the shear method and bottom tracking measurements, and generally appear to be in geostrophic balance. The responses of the acoustic backscatter index and optical turbidity signals appear to be linked to changes of the particle size distribution in the water column. Significantly, this study shows the interest of using a glider-ADCP for coastal zone monitoring. However, the comparison between suspended particulate matter dynamics from satellites and gliders also suggests that a synoptic view of the processes involved requires a multiplatform approach, especially in systems with high spatial and temporal variability, such as the Rhone ROFI area

EuroGOOS roadmap for operational coastal downstream services

The EuroGOOS Coastal working group examines the entire coastal value chain from coastal observations to services for coastal users. The main objective of the working group is to review the status quo, identify gaps and future steps needed to secure and improve the sustainability of the European coastal service provision. Within this framework, our white paper defines a EuroGOOS roadmap for sustained “community coastal downstream service” provision, provided by a broad EuroGOOS community with focus on the national and local scale services. After defining the coastal services in this context, we describe the main components of coastal service provision and explore community benefits and requirements through sectoral examples (aquaculture, coastal tourism, renewable energy, port, cross-sectoral) together with the main challenges and barriers to user uptake. Technology integration challenges are outlined with respect to multiparameter observations, multi-platform observations, the land-coast-ocean continuum, and multidisciplinary data integration. Finally, the technological, financial, and institutional sustainability of coastal observing and coastal service provision are discussed. The paper gives special attention to the delineation of upstream and downstream services, public-private partnerships and the important role of Copernicus in better covering the coastal zone. Therefore, our white paper is a policy and practice review providing a comprehensive overview, in-depth discussion and actionable recommendations (according to key short-term or medium-term priorities) on the envisaged elements of a roadmap for sustained coastal service provision. EuroGOOS, as an entity that unites European national operational oceanography centres, research institutes and scientists across various domains within the broader field of operational oceanography, offers to be the engine and intermediary for the knowledge transfer and communication of experiences, best practices and information, not only amongst its members, but also amongst the different (research) infrastructures, institutes and agencies that have interests in coastal oceanography in Europe

Collaborative Database to Track Mass Mortality Events in the Mediterranean Sea

Anthropogenic climate change, and global warming in particular, has strong and increasing impacts on marine ecosystems (Poloczanska et al., 2013; Halpern et al., 2015; Smale et al., 2019). The Mediterranean Sea is considered a marine biodiversity hot-spot contributing to more than 7% of world's marine biodiversity including a high percentage of endemic species (Coll et al., 2010). The Mediterranean region is a climate change hotspot, where the respective impacts of warming are very pronounced and relatively well documented (Cramer et al., 2018). One of the major impacts of sea surface temperature rise in the marine coastal ecosystems is the occurrence of mass mortality events (MMEs). The first evidences of this phenomenon dated from the first half of'80 years affecting the Western Mediterranean and the Aegean Sea (Harmelin, 1984; Bavestrello and Boero, 1986; Gaino and Pronzato, 1989; Voultsiadou et al., 2011). The most impressive phenomenon happened in 1999 when an unprecedented large scale MME impacted populations of more than 30 species from different phyla along the French and Italian coasts (Cerrano et al., 2000; Perez et al., 2000). Following this event, several other large scale MMEs have been reported, along with numerous other minor ones, which are usually more restricted in geographic extend and/or number of affected species (Garrabou et al., 2009; Rivetti et al., 2014; Marbà et al., 2015; Rubio-Portillo et al., 2016, authors' personal observations). These events have generally been associated with strong and recurrent marine heat waves (Crisci et al., 2011; Kersting et al., 2013; Turicchia et al., 2018; Bensoussan et al., 2019) which are becoming more frequent globally (Smale et al., 2019). Both field observations and future projections using Regional Coupled Models (Adloff et al., 2015; Darmaraki et al., 2019) show the increase in Mediterranean sea surface temperature, with more frequent occurrence of extreme ocean warming events. As a result, new MMEs are expected during the coming years. To date, despite the efforts, neither updated nor comprehensive information can support scientific analysis of mortality events at a Mediterranean regional scale. Such information is vital to guide management and conservation strategies that can then inform adaptive management schemes that aim to face the impacts of climate change.MV-L was supported by a postdoctoral contract Juan de la Cierva-Incorporación (IJCI-2016-29329) of Ministerio de Ciencia, Innovación y Universidades. AI was supported by a Technical staff contract (PTA2015-10829-I) Ayudas Personal Técnico de Apoyo of Ministerio de Economía y Competitividad (2015). Interreg Med Programme (grant number Project MPA-Adapt 1MED15_3.2_M2_337) 85% cofunded by the European Regional Development Fund, the MIMOSA project funded by the Foundation Prince Albert II Monaco and the European Union's Horizon 2020 research and innovation programme under grant agreement no 689518 (MERCES). DG-G was supported by an FPU grant (FPU15/05457) from the Spanish Ministry of Education. J-BL was partially supported by the Strategic Funding UID/Multi/04423/2013 through national funds provided by FCT - Foundation for Science and Technology and European Regional Development Fund (ERDF), in the framework of the programme PT2020

Consultation institutionnelle avant-projet du contrat de baie des îles d'or

Cet avant-projet, fruit d'un intense travail de concertation participative de l'ensemble des acteurs mobilisés, clarifie à l'échelle du territoire des îles d'or les solidarités écologiques entre les îles et le territoire

Modélisation et analyse de la marée interne dans le golfe de Gascogne

Interactions of barotropic tidal currents with continental shelves result in the generation of internal tides. Important energy transfers are associated together with mixing. This enables the preservation of the oceanic general circulation. Large amplitude internal tides of the Bay of Biscay are presented for the MINT94 SHOM experiment modelling using the 3D coastal ocean model SYMPHONIE. Generation and propagation properties of semi-diurnal and quarter-diurnal internal tides and the origin of non linear tides are investigated thanks to the development of the WEof analysis tool (Wavelet Empirical orthogonal function). It combines wavelet analysis (time-frequency localization) and principal components analysis (coherent physical pattern recognition). Sensitivity studies are carried out in order to investigate the contributions of the following forcing over internal tides: barotropic tides, bathymetry and thermohaline stratification.L'interaction des courants de marée barotrope avec les talus continentaux est à l'origine de la génération d'ondes internes. D'importants transferts d'énergie et du mélange y sont associés, permettant le maintien de la circulation océanique générale. La modélisation des marées internes de grande amplitude du golfe de Gascogne de la campagne MINT94 du SHOM est réalisée à l'aide du modèle 3D côtier SYMPHONIE. Les propriétés de génération et de propagation des marées internes semi-diurnes et quart-diurnes, l'origine des ondes non-linéaires, sont présentées suite au développement de l'outil d'analyse WEof (Wavelet Empirical orthogonal function). Il combine analyse en ondelettes (localisation temps-fréquence) et analyse en composantes principales (identification des structures physiques cohérentes). Des études de sensibilité sont présentées indiquant l'influence sur la marée interne des contributions suivantes: forçage par la marée barotrope, bathymétrie et stratification thermohaline

Rapport des campagnes TURBIDENT Leg1 (Mai 2018) & Leg2 (Octobre 2018)

This report reviews the data obtained during Leg1 and Leg2 of the TURBIDENT oceanographic campaign (May-October 2018) carried out in the Iles d'Or (Toulon) area to the Banc des Blauquières (Cassis), within the framework of the ANR ASTRID Turbdident. The objective of this campaign was to acquire an innovative data set providing relevant information on the ocean surface layer under the illumination zone of the MIO HF radar, in particular sub-surface current profiles obtained using acoustic Doppler current meters (ADCP) operating in a stabilised manner below the surface from an autonomous underwater vehicle (AUV) from Ifremer, and temperature profiles obtained using low-cost thermistor lines developed in-house, in addition to more conventional measurements of hydrological profiles, towed ADCP and current-meter mooring.Ce rapport dresse le bilan des données obtenues durant les Legs 1 et 2 de la campagne océanographique TURBIDENT (mai-octobre 2018) réalisée dans la zone des Iles d'Or (Toulon) au Banc des Blauquières (Cassis), dans le cadre de l'ANR ASTRID Turbdident. L’objectif de cette campagne était d’acquérir un jeu de données novateur permettant d’apporter une information pertinente sur la couche de surface océanique sous la zone d’illumination du radar HF du MIO, notamment des profils de courant sub-superficiels obtenus à l’aide de courantomètres acoustiques Doppler (ADCP) opérant de façon stabilisée sous la surface depuis un engin sous-marin autonome (AUV) de l’Ifremer, et des profils de températures obtenus à l’aide de lignes de thermistances à bas coût développées en interne, en plus de la réalisation de mesures plus classiques de profils hydrologiques, ADCP tracté et mouillage courantométrique

Combined wavelet and principal component analysis (WEof) of a scale oriented model of coastal ocean gravity waves

Coastal ocean numerical modeling is basically the representation of the dynamics of the coastal ocean in a chosen range of length scales and over an associated frequency band, including the modeling of both coherent processes and associated transient processes. The ocean dynamical features can be individually identified by combining wavelet analysis for time and frequency localization and principal component analysis to “decorrelate” physically consistent structures. In the present paper, the so-called WEof analysis is applied for the extraction of external gravity waves and internal gravity wave lower modes in a simple case of a flat bottom, constant Brunt-Väisälä ocean. It is shown that, with some well known restrictive assumptions, WEof analysis is an efficient candidate for the recognition of frequency localized dynamical processes

Study of high frequency measurements from the MesuRho mooring

The high frequency MesuRho station, part of the MAREL network and located at the mouth of the Rhone River is presented. Measures sometimes show bias signs, drift or double, so that a graphical interface was implemented to quickly visualize data and eventually correct them. Original data set and corrected data for 2009-2013 are presented, the methods of corrections provided are detailed. Finally an example of a storm event study (under strong south east wind) between the 4th and the 7th of March 2013 is presented and some prospects to improve data management are proposed.La station haute fréquence MesuRho appartenant au réseau MAREL et située à l'embouchure du Rhône est présentée. Les mesures présentant parfois des signes de biais, de dérive ou de doubles, une interface graphique à été mise en place afin de visualiser rapidement les données et éventuellement de les corriger. Les jeux de données d'origine et corrigées 2009-2013 sont présentés, les méthodes de corrections mise à disposition sont détaillées. Enfin, l’étude d'un évènement de tempête (coup de vent d'Est) entre le 4 et le 7 Mars 2013 est présentée à titre d’exemple, et quelques perspectives en vue d'améliorer la gestion des données sont proposées