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

Diatom DNA metabarcoding for ecological assessment: Comparison among bioinformatics pipelines used in six European countries reveals the need for standardization

Ecological assessment of lakes and rivers using benthic diatom assemblages currently requires considerable taxonomic expertise to identify species using light microscopy. This traditional approach is also time-consuming. Diatom metabarcoding is a promising alternative and there is increasing interest in using this approach for routine assessment. However, until now, analysis protocols for diatom metabarcoding have been developed and optimised by research groups working in isolation. The diversity of existing bioinformatics methods highlights the need for an assessment of the performance and comparability of results of different methods. The aim of this study was to test the correspondence of outputs from six bioinformatics pipelines currently in use for diatom metabarcoding in different European countries. Raw sequence data from 29 biofilm samples were treated by each of the bioinformatics pipelines, five of them using the same curated reference database. The outputs of the pipelines were compared in terms of sequence unit assemblages, taxonomic assignment, biotic index score and ecological assessment outcomes. The three last components were also compared to outputs from traditional light microscopy, which is currently accepted for ecological assessment of phytobenthos, as required by the Water Framework Directive. We also tested the performance of the pipelines on the two DNA markers (rbcL and 185-V4) that are currently used by the working groups participating in this study. The sequence unit assemblages produced by different pipelines showed significant differences in terms of assigned and unassigned read numbers and sequence unit numbers. When comparing the taxonomic assignments at genus and species level, correspondence of the taxonomic assemblages between pipelines was weak. Most discrepancies were linked to differential detection or quantification of taxa, despite the use of the same reference database. Subsequent calculation of biotic index scores also showed significant differences between approaches, which were reflected in the final ecological assessment. Use of the rbcL marker always resulted in better correlation among molecular datasets and also in results closer to these generated using traditional microscopy. This study shows that decisions made in pipeline design have implications for the dataset's structure and the taxonomic assemblage, which in turn may affect biotic index calculation and ecological assessment. There is a need to define best-practice bioinformatics parameters in order to ensure the best representation of diatom assemblages. Only the use of similar parameters will ensure the compatibility of data from different working groups. The future of diatom metabarcoding for ecological assessment may also lie in the development of new metrics using, for example, presence/absence instead of relative abundance data. (C) 2020 The Authors. Published by Elsevier B.V

The seeds of divergence: the economy of French North America, 1688 to 1760

Generally, Canada has been ignored in the literature on the colonial origins of divergence with most of the attention going to the United States. Late nineteenth century estimates of income per capita show that Canada was relatively poorer than the United States and that within Canada, the French and Catholic population of Quebec was considerably poorer. Was this gap long standing? Some evidence has been advanced for earlier periods, but it is quite limited and not well-suited for comparison with other societies. This thesis aims to contribute both to Canadian economic history and to comparative work on inequality across nations during the early modern period. With the use of novel prices and wages from Quebec—which was then the largest settlement in Canada and under French rule—a price index, a series of real wages and a measurement of Gross Domestic Product (GDP) are constructed. They are used to shed light both on the course of economic development until the French were defeated by the British in 1760 and on standards of living in that colony relative to the mother country, France, as well as the American colonies. The work is divided into three components. The first component relates to the construction of a price index. The absence of such an index has been a thorn in the side of Canadian historians as it has limited the ability of historians to obtain real values of wages, output and living standards. This index shows that prices did not follow any trend and remained at a stable level. However, there were episodes of wide swings—mostly due to wars and the monetary experiment of playing card money. The creation of this index lays the foundation of the next component. The second component constructs a standardized real wage series in the form of welfare ratios (a consumption basket divided by nominal wage rate multiplied by length of work year) to compare Canada with France, England and Colonial America. Two measures are derived. The first relies on a “bare bones” definition of consumption with a large share of land-intensive goods. This measure indicates that Canada was poorer than England and Colonial America and not appreciably richer than France. However, this measure overestimates the relative position of Canada to the Old World because of the strong presence of land-intensive goods. A second measure is created using a “respectable” definition of consumption in which the basket includes a larger share of manufactured goods and capital-intensive goods. This second basket better reflects differences in living standards since the abundance of land in Canada (and Colonial America) made it easy to achieve bare subsistence, but the scarcity of capital and skilled labor made the consumption of luxuries and manufactured goods (clothing, lighting, imported goods) highly expensive. With this measure, the advantage of New France over France evaporates and turns slightly negative. In comparison with Britain and Colonial America, the gap widens appreciably. This element is the most important for future research. By showing a reversal because of a shift to a different type of basket, it shows that Old World and New World comparisons are very sensitive to how we measure the cost of living. Furthermore, there are no sustained improvements in living standards over the period regardless of the measure used. Gaps in living standards observed later in the nineteenth century existed as far back as the seventeenth century. In a wider American perspective that includes the Spanish colonies, Canada fares better. The third component computes a new series for Gross Domestic Product (GDP). This is to avoid problems associated with using real wages in the form of welfare ratios which assume a constant labor supply. This assumption is hard to defend in the case of Colonial Canada as there were many signs of increasing industriousness during the eighteenth and nineteenth centuries. The GDP series suggest no long-run trend in living standards (from 1688 to circa 1765). The long peace era of 1713 to 1740 was marked by modest economic growth which offset a steady decline that had started in 1688, but by 1760 (as a result of constant warfare) living standards had sunk below their 1688 levels. These developments are accompanied by observations that suggest that other indicators of living standard declined. The flat-lining of incomes is accompanied by substantial increases in the amount of time worked, rising mortality and rising infant mortality. In addition, comparisons of incomes with the American colonies confirm the results obtained with wages— Canada was considerably poorer. At the end, a long conclusion is provides an exploratory discussion of why Canada would have diverged early on. In structural terms, it is argued that the French colony was plagued by the problem of a small population which prohibited the existence of scale effects. In combination with the fact that it was dispersed throughout the territory, the small population of New France limited the scope for specialization and economies of scale. However, this problem was in part created, and in part aggravated, by institutional factors like seigneurial tenure. The colonial origins of French America’s divergence from the rest of North America are thus partly institutional

Apport des planeurs sous-marins pour le suivi des processus hydro-sédimentaires de la zone côtière

The dynamics of suspended particulate matter play a major role in water quality, carbon fluxes and ecosystem dynamics in the coastal ocean. However, the interlocking spatial (from meters to hundreds of kilometers) and temporal (from seconds to months) scales of coastal processes make the study of hydro-sedimentary dynamics challenging, especially during extreme events such as storms and floods. Improving our ability to understand, simulate and predict sediment dynamics in the coastal zone requires improving the resolution, extent and duration of oceanographic measurements. In this context, the contribution of autonomous underwater gliders, which allow the observation of fine-scale hydrology and hydrodynamics over part or all of the continental shelf, and over long periods of time, is investigated. The objective of this thesis is to develop the processing chain and to explore the capability of a glider newly equipped with an acoustic Doppler current profiler to study hydro-sedimentary processes, particularly during extreme events. The methodology used is based on a combined analysis of data from traditional platforms (moorings, ships, satellites), numerical simulations and data acquired in situ from gliders, through experiments conducted in the Rhone plume (2016 and 2017 campaigns) and on the continental shelf of the Gulf of Lion (2018). The thesis details the development and validation of a processing chain allowing the simultaneous analysis of hydrological and hydrodynamic data from underwater gliders. This open-source code of this “toolbox” was made available to the community on the GitHub platform. The first experiment detailed (i) the fine-scale hydrological and hydrodynamic structures of the region under the influence of the Rhone plume, (ii) the contribution of acoustic and optical measurements to differentiate the granulometric populations (fine vs. aggregates) of suspended particles, and (iii) the complementarity with satellite ocean colour data. The second experiment observed the spatiotemporal variability of currents and sediment dynamics induced by a strong easterly storm on the continental shelf. Coupled with numerical modeling, it highlighted the role of waves on resuspension on the outer shelf and made it possible to characterize the trajectories and extent of particle transport during this energetic event. The results clearly demonstrate the interest of gliders equipped with optical and acoustic sensors for monitoring currents and turbidity in the coastal zone over periods of several weeks to several months, essential for capturing episodic flood and storm events, the main drivers of sediment dynamics.La dynamique de la matière en suspension joue un rôle majeur dans la qualité de l’eau, les flux de carbone et la dynamique des écosystèmes de l’océan côtier. Cependant, l’imbrication des échelles spatiales (du mètre à la centaine de kilomètres) et temporelles (de la seconde à plusieurs mois) des processus côtiers rend l’étude de la dynamique hydro-sédimentaire délicate, notamment lors d’événements extrêmes, comme les tempêtes et les crues. L’amélioration de notre capacité à comprendre, simuler et prévoir la dynamique des sédiments dans la zone côtière nécessite d’améliorer la résolution, l’étendue et la durée des mesures océanographiques. Dans ce contexte, l’apport des planeurs sous-marins autonomes est examiné, leur conception permettant d’observer sur des périodes longues et à fine échelle l’hydrologie et l’hydrodynamique d’une partie ou de l’ensemble du plateau continental. L’objectif de cette thèse est d’élaborer une chaîne de traitement et d’explorer la capacité d’un planeur nouvellement équipé d’un profileur de courant acoustique à effet Doppler pour l’étude des processus hydro-sédimentaires, en particulier lors d’événements extrêmes. La méthodologie utilisée se base sur une analyse combinatoire de données provenant de plateformes traditionnelles (mouillages, navires, satellites), de simulations numériques et de données acquises in situ à partir des planeurs, au travers d’expériences conduites au niveau du panache rhodanien (campagnes de 2016 et 2017) et sur le plateau continental du Golfe du Lion (2018). La thèse détaille le développement et la validation d’une chaîne de traitement permettant d’analyser simultanément les données hydrologiques et hydrodynamiques de planeurs sous-marins. Le code source libre de cette « boîte à outils » a été mis à disposition de la communauté sur la plateforme GitHub. La première expérience a permis de détailler (i) les structures hydrologiques et hydrodynamiques à fine échelle de la région sous influence du panache du Rhône, (ii) l’apport des mesures acoustiques et optiques pour différentier les populations granulométriques (fines vs. agrégats) des particules en suspension, et enfin (iii) la complémentarité avec les données satellites de couleur de l’eau. La seconde expérience a permis d’observer la variabilité spatio-temporelle des courants et de la dynamique sédimentaire induits par une tempête d’est sur le plateau continental. Couplée à la modélisation numérique, elle a mis en évidence le rôle des vagues sur la resuspension au niveau du plateau externe, et permis de caractériser les trajectoires et l’étendue du transport particulaire durant cet événement énergétique. Ces résultats démontrent clairement l’intérêt des planeurs équipés de capteurs optiques et acoustiques pour le suivi des courants et de la turbidité dans la zone côtière sur des périodes de plusieurs semaines à plusieurs mois, essentiels pour capter des événements épisodiques de crues et tempêtes, principaux moteurs de la dynamique sédimentaire

Apport des planeurs sous-marins pour le suivi des processus hydro-sédimentaires de la zone côtière

The dynamics of suspended particulate matter play a major role in water quality, carbon fluxes and ecosystem dynamics in the coastal ocean. However, the interlocking spatial (from meters to hundreds of kilometers) and temporal (from seconds to months) scales of coastal processes make the study of hydro-sedimentary dynamics challenging, especially during extreme events such as storms and floods. Improving our ability to understand, simulate and predict sediment dynamics in the coastal zone requires improving the resolution, extent and duration of oceanographic measurements. In this context, the contribution of autonomous underwater gliders, which allow the observation of fine-scale hydrology and hydrodynamics over part or all of the continental shelf, and over long periods of time, is investigated. The objective of this thesis is to develop the processing chain and to explore the capability of a glider newly equipped with an acoustic Doppler current profiler to study hydro-sedimentary processes, particularly during extreme events. The methodology used is based on a combined analysis of data from traditional platforms (moorings, ships, satellites), numerical simulations and data acquired in situ from gliders, through experiments conducted in the Rhone plume (2016 and 2017 campaigns) and on the continental shelf of the Gulf of Lion (2018). The thesis details the development and validation of a processing chain allowing the simultaneous analysis of hydrological and hydrodynamic data from underwater gliders. This open-source code of this “toolbox” was made available to the community on the GitHub platform. The first experiment detailed (i) the fine-scale hydrological and hydrodynamic structures of the region under the influence of the Rhone plume, (ii) the contribution of acoustic and optical measurements to differentiate the granulometric populations (fine vs. aggregates) of suspended particles, and (iii) the complementarity with satellite ocean colour data. The second experiment observed the spatiotemporal variability of currents and sediment dynamics induced by a strong easterly storm on the continental shelf. Coupled with numerical modeling, it highlighted the role of waves on resuspension on the outer shelf and made it possible to characterize the trajectories and extent of particle transport during this energetic event. The results clearly demonstrate the interest of gliders equipped with optical and acoustic sensors for monitoring currents and turbidity in the coastal zone over periods of several weeks to several months, essential for capturing episodic flood and storm events, the main drivers of sediment dynamics.La dynamique de la matière en suspension joue un rôle majeur dans la qualité de l’eau, les flux de carbone et la dynamique des écosystèmes de l’océan côtier. Cependant, l’imbrication des échelles spatiales (du mètre à la centaine de kilomètres) et temporelles (de la seconde à plusieurs mois) des processus côtiers rend l’étude de la dynamique hydro-sédimentaire délicate, notamment lors d’événements extrêmes, comme les tempêtes et les crues. L’amélioration de notre capacité à comprendre, simuler et prévoir la dynamique des sédiments dans la zone côtière nécessite d’améliorer la résolution, l’étendue et la durée des mesures océanographiques. Dans ce contexte, l’apport des planeurs sous-marins autonomes est examiné, leur conception permettant d’observer sur des périodes longues et à fine échelle l’hydrologie et l’hydrodynamique d’une partie ou de l’ensemble du plateau continental. L’objectif de cette thèse est d’élaborer une chaîne de traitement et d’explorer la capacité d’un planeur nouvellement équipé d’un profileur de courant acoustique à effet Doppler pour l’étude des processus hydro-sédimentaires, en particulier lors d’événements extrêmes. La méthodologie utilisée se base sur une analyse combinatoire de données provenant de plateformes traditionnelles (mouillages, navires, satellites), de simulations numériques et de données acquises in situ à partir des planeurs, au travers d’expériences conduites au niveau du panache rhodanien (campagnes de 2016 et 2017) et sur le plateau continental du Golfe du Lion (2018). La thèse détaille le développement et la validation d’une chaîne de traitement permettant d’analyser simultanément les données hydrologiques et hydrodynamiques de planeurs sous-marins. Le code source libre de cette « boîte à outils » a été mis à disposition de la communauté sur la plateforme GitHub. La première expérience a permis de détailler (i) les structures hydrologiques et hydrodynamiques à fine échelle de la région sous influence du panache du Rhône, (ii) l’apport des mesures acoustiques et optiques pour différentier les populations granulométriques (fines vs. agrégats) des particules en suspension, et enfin (iii) la complémentarité avec les données satellites de couleur de l’eau. La seconde expérience a permis d’observer la variabilité spatio-temporelle des courants et de la dynamique sédimentaire induits par une tempête d’est sur le plateau continental. Couplée à la modélisation numérique, elle a mis en évidence le rôle des vagues sur la resuspension au niveau du plateau externe, et permis de caractériser les trajectoires et l’étendue du transport particulaire durant cet événement énergétique. Ces résultats démontrent clairement l’intérêt des planeurs équipés de capteurs optiques et acoustiques pour le suivi des courants et de la turbidité dans la zone côtière sur des périodes de plusieurs semaines à plusieurs mois, essentiels pour capter des événements épisodiques de crues et tempêtes, principaux moteurs de la dynamique sédimentaire

Contribution of autonomous underwater gliders to monitor suspended particulates matter dynamics in the coastal zone

La dynamique de la matière en suspension joue un rôle majeur dans la qualité de l’eau, les flux de carbone et la dynamique des écosystèmes de l’océan côtier. Cependant, l’imbrication des échelles spatiales (du mètre à la centaine de kilomètres) et temporelles (de la seconde à plusieurs mois) des processus côtiers rend l’étude de la dynamique hydro-sédimentaire délicate, notamment lors d’événements extrêmes, comme les tempêtes et les crues. L’amélioration de notre capacité à comprendre, simuler et prévoir la dynamique des sédiments dans la zone côtière nécessite d’améliorer la résolution, l’étendue et la durée des mesures océanographiques. Dans ce contexte, l’apport des planeurs sous-marins autonomes est examiné, leur conception permettant d’observer sur des périodes longues et à fine échelle l’hydrologie et l’hydrodynamique d’une partie ou de l’ensemble du plateau continental. L’objectif de cette thèse est d’élaborer une chaîne de traitement et d’explorer la capacité d’un planeur nouvellement équipé d’un profileur de courant acoustique à effet Doppler pour l’étude des processus hydro-sédimentaires, en particulier lors d’événements extrêmes. La méthodologie utilisée se base sur une analyse combinatoire de données provenant de plateformes traditionnelles (mouillages, navires, satellites), de simulations numériques et de données acquises in situ à partir des planeurs, au travers d’expériences conduites au niveau du panache rhodanien (campagnes de 2016 et 2017) et sur le plateau continental du Golfe du Lion (2018). La thèse détaille le développement et la validation d’une chaîne de traitement permettant d’analyser simultanément les données hydrologiques et hydrodynamiques de planeurs sous-marins. Le code source libre de cette « boîte à outils » a été mis à disposition de la communauté sur la plateforme GitHub. La première expérience a permis de détailler (i) les structures hydrologiques et hydrodynamiques à fine échelle de la région sous influence du panache du Rhône, (ii) l’apport des mesures acoustiques et optiques pour différentier les populations granulométriques (fines vs. agrégats) des particules en suspension, et enfin (iii) la complémentarité avec les données satellites de couleur de l’eau. La seconde expérience a permis d’observer la variabilité spatio-temporelle des courants et de la dynamique sédimentaire induits par une tempête d’est sur le plateau continental. Couplée à la modélisation numérique, elle a mis en évidence le rôle des vagues sur la resuspension au niveau du plateau externe, et permis de caractériser les trajectoires et l’étendue du transport particulaire durant cet événement énergétique. Ces résultats démontrent clairement l’intérêt des planeurs équipés de capteurs optiques et acoustiques pour le suivi des courants et de la turbidité dans la zone côtière sur des périodes de plusieurs semaines à plusieurs mois, essentiels pour capter des événements épisodiques de crues et tempêtes, principaux moteurs de la dynamique sédimentaire.The dynamics of suspended particulate matter play a major role in water quality, carbon fluxes and ecosystem dynamics in the coastal ocean. However, the interlocking spatial (from meters to hundreds of kilometers) and temporal (from seconds to months) scales of coastal processes make the study of hydro-sedimentary dynamics challenging, especially during extreme events such as storms and floods. Improving our ability to understand, simulate and predict sediment dynamics in the coastal zone requires improving the resolution, extent and duration of oceanographic measurements. In this context, the contribution of autonomous underwater gliders, which allow the observation of fine-scale hydrology and hydrodynamics over part or all of the continental shelf, and over long periods of time, is investigated. The objective of this thesis is to develop the processing chain and to explore the capability of a glider newly equipped with an acoustic Doppler current profiler to study hydro-sedimentary processes, particularly during extreme events. The methodology used is based on a combined analysis of data from traditional platforms (moorings, ships, satellites), numerical simulations and data acquired in situ from gliders, through experiments conducted in the Rhone plume (2016 and 2017 campaigns) and on the continental shelf of the Gulf of Lion (2018). The thesis details the development and validation of a processing chain allowing the simultaneous analysis of hydrological and hydrodynamic data from underwater gliders. This open-source code of this “toolbox” was made available to the community on the GitHub platform. The first experiment detailed (i) the fine-scale hydrological and hydrodynamic structures of the region under the influence of the Rhone plume, (ii) the contribution of acoustic and optical measurements to differentiate the granulometric populations (fine vs. aggregates) of suspended particles, and (iii) the complementarity with satellite ocean colour data. The second experiment observed the spatiotemporal variability of currents and sediment dynamics induced by a strong easterly storm on the continental shelf. Coupled with numerical modeling, it highlighted the role of waves on resuspension on the outer shelf and made it possible to characterize the trajectories and extent of particle transport during this energetic event. The results clearly demonstrate the interest of gliders equipped with optical and acoustic sensors for monitoring currents and turbidity in the coastal zone over periods of several weeks to several months, essential for capturing episodic flood and storm events, the main drivers of sediment dynamics

Quels modes d’intervention pour soutenir la discussion sur le travail dans les organisations ?

National audienceIn response to the rise of subjective pain at work, many studies call for the opening of work discussion spaces. First proposals for the design of these spaces are already available. However, the questions of their design, of their setting and of learning new collective modes of action, remain unclear. How to intervene so that discussion processes are robust and durable in organizations ? These issues will be investigated through an intervention in a private hospital that faces a deterioration of its social climate. This paper presents initially the vision of the organization on which the interventional device is founded, namely the organization viewed as a space to mediate or to regulate. This perspective requires, in a specific managerial approach, to think the structuring and leading of joint regulation spaces. The article describes then the research-intervention and the context in which it took place, before presenting the intervention devices concretely implemented in the clinic. It highlights that opening work discussion spaces involves the development of a new conventional substrate that can be a cognitive support for discussion. The aim is to undertake a managerial communication based on dialogue, a decision mode based on collegiality and a relationship to authority that allows subsidiarity.Face à la montée des maux subjectifs du travail, de nombreux travaux appellent à l’ouverture d’espaces de discussion sur le travail. Si on dispose déjà de premières propositions concernant le design de ces espaces, la question de leur mise en place et de l’apprentissage des nouveaux modes d’action collective qu’ils supposent reste à élucider. Comment intervenir de telle manière que les processus de discussion soient robustes et pérennes dans l’organisation ? Ces questions seront instruites à partir d’une intervention dans une clinique confrontée à une dégradation de son climat social. L’article présente dans un premier temps la vision de l’organisation dans laquelle les dispositifs d’intervention déployés trouvent leur origine, à savoir l’organisation vue comme un espace à médier ou à réguler. Une telle perspective suppose, dans une approche spécifiquement gestionnaire, de penser la structuration et le pilotage d’espaces de régulation conjointe. L’article décrit ensuite la recherche-intervention et le contexte dans lequel elle s’est déroulée avant de présenter les dispositifs d’intervention concrètement mis en place dans la clinique. Il met en évidence que l’ouverture d’espaces de discussion pérennes suppose le développement d’un nouveau substrat conventionnel propre à servir de soubassement cognitif à la discussion et dont l’enjeu est de mettre en œuvre une communication managériale fondée sur le dialogue, des modalités de prise de décision s’appuyant sur la collégialité et un rapport à l’autorité permettant la subsidiarité

Internal solitary waves on the NW African shelf: A heuristic approach to localize diapycnal mixing hotspots

Turbulent mixing on continental shelves plays roles in the structure and dynamics of marine ecosystems, nutrient cycling, primary production and dispersion of pollutants. Describing and understanding internal wave dynamics enables improved mapping of mixing over continental shelves, especially in complex environments where many processes may interact, such as in upwelling systems. This paper describes internal wave propagation and dissipation in the Moroccan upwelling system using a comprehensive set of hydrographic observations made during two in situ surveys. The acoustic backscatter of the echosounder is shown to be a rapid and convenient survey tool for detecting internal solitary waves (ISWs) on large spatial scales, through the high-frequency oscillation of the zooplankton layer during nighttime conditions. Along ISW trains, enhanced diapycnal mixing episodes are observed with increased dissipation coefficients in the thermocline (O(10-7 W kg-1)), associated with overturning up to 6 m. Mixing due to internal wave soliton packets shows large spatial and temporal variability, but contributes to the overall mixing processes and is responsible for large intermittent variations in the thermocline position. The joint use of a multifrequency echosounder and a current profiler ADCP allows mixing to be quantified (via the Richardson number) on large spatial scales. Validation and use of this method in other coastal regions could be useful to determine regional mixing parameterization in numerical models

Sediment dynamics on the outer-shelf of the Gulf of Lions during a storm: An approach based on acoustic glider and numerical modeling

International audienceDescribing and quantifying storm-induced sediment dynamics enables improved mapping of the fate of sediments over continental shelves, which is necessary to understand their role in the structure and dynamics of marine ecosystems, nutrient cycling, and dispersion of pollutants. Storms are episodic processes that can lead to massive sediment resuspension and transport on continental shelves. However, understanding sediment dynamics during storms remains a challenge, because these events are spatially under-sampled due to their intermittency and intensity. This paper quantifies processes that drive sediment dynamics and their spatiotemporal variability over the outer shelf of the Gulf of Lions (NW Mediterranean), during a 5-year return period storm, using an active acoustic glider combined with a hydrodynamic model (SYMPHONIE) and wave model (WAVEWATCH-III). The glider-ADCP (Acoustic Doppler Current Profiler) measurements proved invaluable validation of current vertical profiles of the hydrodynamic model during this episodic event. The combination of observations with numerical simulations suggest that sediment resuspension is an important process at depths greater than 90 m on the shelf. This appears to be primarily due to the wave forcing, which most likely accounts for some of the observed increase in suspended particulate matter in the water column. At the regional scale, an along shelf sediment transfer by successive jumps associated with onshore storms is suggested, from the main input (the Rhone River) to the output (the Cap de Creus) area of the Gulf of Lions' shelf. This study highlights the complementarity between numerical modeling and new observation instrument designed to spatially extend the measurement of current and turbidity to study sediment resuspension and transport during extreme events on continental shelves