Multidisciplinary investigation on cold seeps with vigorous gas emissions in the Sea of Marmara (MarsiteCruise): Strategy for site detection and sampling and first scientific outcome

MarsiteCruise was undertaken in October/November 2014 in the Sea of Marmara to gain detailed insight into the fate of fluids migrating within the sedimentary column and partially released into the water column. The overall objective of the project was to achieve a more global understanding of cold-seep dynamics in the context of a major active strike-slip fault. Five remotely operated vehicle (ROV) dives were performed at selected areas along the North Anatolian Fault and inherited faults. To efficiently detect, select and sample the gas seeps, we applied an original procedure. It combines sequentially (1) the acquisition of ship-borne multibeam acoustic data from the water column prior to each dive to detect gas emission sites and to design the tracks of the ROV dives, (2) in situ and real-time Raman spectroscopy analysis of the gas stream, and (3) onboard determination of molecular and isotopic compositions of the collected gas bubbles. The in situ Raman spectroscopy was used as a decision-making tool to evaluate the need for continuing with the sampling of gases from the discovered seep, or to move to another one. Push cores were gathered to study buried carbonates and pore waters at the surficial sediment, while CTD-Rosette allowed collecting samples to measure dissolved-methane concentration within the water column followed by a comparison with measurements from samples collected with the submersible Nautile during the Marnaut cruise in 2007. Overall, the visited sites were characterized by a wide diversity of seeps. CO2- and oil-rich seeps were found at the westernmost part of the sea in the Tekirdag Basin, while amphipods, anemones and coral populated the sites visited at the easternmost part in the Cinarcik Basin. Methane-derived authigenic carbonates and bacterial mats were widespread on the seafloor at all sites with variable size and distributions. The measured methane concentrations in the water column were up to 377 μmol, and the dissolved pore-water profiles indicated the occurrence of sulfate depleting processes accompanied with carbonate precipitation. The pore-water profiles display evidence of biogeochemical transformations leading to the fast depletion of seawater sulfate within the first 25-cm depth of the sediment. These results show that the North Anatolian Fault and inherited faults are important migration paths for fluids for which a significant part is discharged into the water column, contributing to the increase of methane concentration at the bottom seawater and favoring the development of specific ecosystems

Structure and Dynamics of Heteroprotein Coacervates

International audienceUnder specific conditions, mixing two oppositely charged proteins induces liquid−liquid phase separation. The denser phase, or coacervate phase, can be potentially applied as a system to protect or encapsulate different bioactive molecules with a broad range of food and/or medical applications. The optimization of the design and efficiency of such systems requires a precise understanding of the structure and the equilibrium of the nanocomplexes formed within the coacervate. Here, we report on the nanocomplexes and the dynamics of the coacervates formed by two well-known, oppositely charged proteins β-lactoglobulin (β-LG, pI ≈ 5.2) and lactoferrin (LF, pI ≈ 8.5). Fluorescence recovery after photobleaching (FRAP) and solid-state nuclear magnetic resonance (NMR) experiments indicate the coexistence of several nanocomplexes as the primary units for the coacervation. To our knowledge, this is the first evidence of the occurrence of an equilibrium between quite unstable nanocomplexes in the coacervate phase. Combined with in silico docking experiments, these data support the fact that coacervation in the present heteroprotein system depends not only on the structural composition of the coacervates but also on the association rates of the proteins forming the nanocomplexes

Assessment of the coupled model CROCO - Wave Watch III in an estuarine environment: Application to the Somme bay

National audienceSediment transport modelling in shallow coastal waters is a challenging topic, especially in macrotidal environments where large intertidal areas are subjected to rapid wave transformation and breaking, complex patterns of tidal currents, and dynamic bedforms. Quantifying the sediment fluxes from the inner shelf to the shoreface is crucial to understand the long-term evolution of such embayements. The bay of Somme, facing the English Channel in North- West France, is a particularly relevant environment to tackle these issues. Known for its megatidal range (up to 10m in spring tides), it is in front of a large subtidal sediment source known as the Picard prism. The intertidal area, more than 6 km-wide, features highly dynamic dune fields and tidal channels. The aim of the study is to evaluate the sediment fluxes between the Picard prism and Bay of Somme using numerical modelling and in-situ observations. The first step is to build a numerical configuration which combines the hydrodynamic model CR OC O, the spectral wave model Wave Watch-III and the USGS sediment transport model. Three nested grids have been created (100m, 30m, 10m) that are forced at the boundaries by tide, wind, wave spectra and river input. Numerical results were tested against ADCP and tidal gauge data. The main conclusions are: i) the flow velocity and the sea surface height are in agreement with observations with a mean RMSE around 0.1m/s and 0.17m for current velocity and sea surface height, respectively ii) a time delay varying between 10 and 30 minutes is observed at some locations, iii) the contribution of the Somme River has very little influence on the results due the low flow discharge for the considered period, iv) the longshore current is well simulated by the coupled model. One of the main limitations of our modeling is due to a bathymetry that was not recorded at the same time as the measurements. Prospects for future work will be to add the USGS sediment transport model in the coupling and to simulate sediment fluxes

Assessment of the Coupled Model CROCO-WaveWatch-III in an Estuarine Environment: application to the Somme Bay (France)

International audienceSediment transport modeling in shallow coastal waters is a challenging topic, especially in macrotidal environments where large intertidal areas are subjected to rapid wave transformation and breaking, complex patterns of tidal currents, and dynamic bedforms. Quantifying the sediment fluxes from the inner shelf to the shoreface is crucial to understand the long-term evolution of such embayment. The bay of Somme, facing the English Channel in North-West France, is a particularly relevant environment to tackle these issues. Known for its megatidal range (up to 10m in spring tides), it is in front of a large subtidal sediment source known as the Picard prism. The intertidal area, more than 6 km-wide, features highly dynamic dune fields and tidal channels. The aim of the study is to evaluate the sediment fluxes between the Picard prism and Bay of Somme using numerical modeling and in-situ observations. The first step is to build a numerical configuration which combines the hydrodynamic model CROCO, the spectral wave model WaveWatch-III and the USGS sediment transport model. Three nested grids have been created (100m, 30m, 10m) that are forced at the boundaries by tide, wind, wave spectra and fluvial discharge. Numerical results were tested against ADCP and tidal gauge data. The main conclusions are: i) the flow velocity and the sea surface height are in agreement with observations with a mean RMSE around 0.1m/s and 0.17m for current velocity and sea surface height, respectively ii) a time delay varying between 10 and 30 minutes is observed at some locations, iii) the contribution of the Somme River has very little influence on the results due the low flow discharge for the considered period, iv) the longshore current is well simulated by the coupled model. One of the main limitations of our modeling is due to a bathymetry that was not recorded at the same time as the measurements. Prospects for future work will be to add the USGS sediment transport model in the coupling and to simulate sediment fluxes

Assessment of the coupled model CROCO - Wave Watch III in an estuarine environment: Application to the Somme bay

National audienceSediment transport modelling in shallow coastal waters is a challenging topic, especially in macrotidal environments where large intertidal areas are subjected to rapid wave transformation and breaking, complex patterns of tidal currents, and dynamic bedforms. Quantifying the sediment fluxes from the inner shelf to the shoreface is crucial to understand the long-term evolution of such embayements. The bay of Somme, facing the English Channel in North- West France, is a particularly relevant environment to tackle these issues. Known for its megatidal range (up to 10m in spring tides), it is in front of a large subtidal sediment source known as the Picard prism. The intertidal area, more than 6 km-wide, features highly dynamic dune fields and tidal channels. The aim of the study is to evaluate the sediment fluxes between the Picard prism and Bay of Somme using numerical modelling and in-situ observations. The first step is to build a numerical configuration which combines the hydrodynamic model CR OC O, the spectral wave model Wave Watch-III and the USGS sediment transport model. Three nested grids have been created (100m, 30m, 10m) that are forced at the boundaries by tide, wind, wave spectra and river input. Numerical results were tested against ADCP and tidal gauge data. The main conclusions are: i) the flow velocity and the sea surface height are in agreement with observations with a mean RMSE around 0.1m/s and 0.17m for current velocity and sea surface height, respectively ii) a time delay varying between 10 and 30 minutes is observed at some locations, iii) the contribution of the Somme River has very little influence on the results due the low flow discharge for the considered period, iv) the longshore current is well simulated by the coupled model. One of the main limitations of our modeling is due to a bathymetry that was not recorded at the same time as the measurements. Prospects for future work will be to add the USGS sediment transport model in the coupling and to simulate sediment fluxes

Multidisciplinary Approach of the Population Dynamics of the Non-Indigenous Species the Mamilla Clam Ruditapes philippinarum Along the Western Coast of Cotentin (Normandy, France)

International audienceSince its introduction in the 1970’ in Chausey (western English Channel), the Mamilla clamRuditapes philippinarum shows an important population increase along the western coast ofCotentin. A distribution mapping in 2015 highlighted the presence of four main patches ofabundance representing 10% of the intertidal zone. Yearly count of recreational fishermenestimates the presence of 6,000 fishermen per day (all activities) during spring tide with anestimate of clam catches of 120 t against 8 t by professional fishermen. To identify the originof such clam population, several hypotheses have been tested to identify the larval source, thelarval dispersion and the recruitment sectors within a hydrodynamic MARS 3 D modelsimulating the hydrodynamic of the area. Then the Ichthyop code is used to simulate thedispersal of clam larvae after a month of planktonic life, with different wind directions, duringthe June-July period. A part of the larvae which is transported offshore, numerous larvaeparticipate to the recruitment of clams of the western coast of Cotentin population. This explainsthe maintaining of important clam stocks in spite of annual harvesting mainly by raking thesediment habitat. Moreover, several experiments (2014-2018) show that about 20% of clamsshow moderated local displacements which can participate to colonise the harvesting areas. Theraking harvesting could also contribute to the clam displacement in removing sediment andclams in large area. All these features are favourable to maintain a sustainable fishery in thisarea with low abundance but in a large intertidal zone

Multidisciplinary Approach of the Population Dynamics of the Non-Indigenous Species the Mamilla Clam Ruditapes philippinarum Along the Western Coast of Cotentin (Normandy, France)

International audienceSince its introduction in the 1970’ in Chausey (western English Channel), the Mamilla clamRuditapes philippinarum shows an important population increase along the western coast ofCotentin. A distribution mapping in 2015 highlighted the presence of four main patches ofabundance representing 10% of the intertidal zone. Yearly count of recreational fishermenestimates the presence of 6,000 fishermen per day (all activities) during spring tide with anestimate of clam catches of 120 t against 8 t by professional fishermen. To identify the originof such clam population, several hypotheses have been tested to identify the larval source, thelarval dispersion and the recruitment sectors within a hydrodynamic MARS 3 D modelsimulating the hydrodynamic of the area. Then the Ichthyop code is used to simulate thedispersal of clam larvae after a month of planktonic life, with different wind directions, duringthe June-July period. A part of the larvae which is transported offshore, numerous larvaeparticipate to the recruitment of clams of the western coast of Cotentin population. This explainsthe maintaining of important clam stocks in spite of annual harvesting mainly by raking thesediment habitat. Moreover, several experiments (2014-2018) show that about 20% of clamsshow moderated local displacements which can participate to colonise the harvesting areas. Theraking harvesting could also contribute to the clam displacement in removing sediment andclams in large area. All these features are favourable to maintain a sustainable fishery in thisarea with low abundance but in a large intertidal zone

3D hydrodynamics of a macro-tidal estuarine environment under wave and tide forcings

The sandy estuaries along the English Channel have been silting up for over 10 years. Former geoscientific studies, which assessed sediment stocks, showed that the sedimentary material came from the marine rather than the fluvial part due intense cross-shore dynamics. To understand how the sedimentary material was brought from the coastal sea from estuary, a three-dimensional coupled numerical model was first set up, before simulating hydrosedimentary processes. This study was applied to the bay of the Somme, located in the northern France along the English Channel. This estuarine environment is forced by semi-diurnal tides and ocean waves, that move the predominant fine and coarse sands. The sands moving from coastal ocean, a numerical validation was carried out at coastal, nearshore, and bay sites using several datasets from in-situ field campaigns. Good agreement was found between model and data in the coastal zone regarding to bottom and surface current, sea surface height and mean wave parameters. Vertical profiles of current were also well simulated, especially their modulation by ocean waves. The nearshore simulations reproduced the wave set-up and wave set-down, as well as the cross-shore dynamics with simulated undertow and streaming, and the longshore dynamics showing the longshore current generated by oblique incident ocean waves. Inside the bay, a modulation of the tidal wave is observed, as expected. The water filling and draining of the bay are well represented and follow the tidal phase: the ebb flow drains the bay while the flood flow fills it. These simulations were performed under calm and storm conditions, enabling us to identify the contribution of ocean waves to the hydrodynamics. The next step is to build the hydro-sedimentary model to assess the impact of hydrodynamics on sediment transport and the morphodynamics of the bay

3D hydrodynamics of a macro-tidal estuarine environment under wave and tide forcings

International audienceThe sandy estuaries along the English Channel have been silting up for over 10 years. Former geoscientific studies, which assessed sediment stocks, showed that the sedimentary material came from the marine rather than the fluvial part due intense cross-shore dynamics. To understand how the sedimentary material was brought from the coastal sea from estuary, a three-dimensional coupled numerical model was first set up, before simulating hydrosedimentary processes. This study was applied to the bay of the Somme, located in the northern France along the English Channel. This estuarine environment is forced by semi-diurnal tides and ocean waves, that move the predominant fine and coarse sands. The sands moving from coastal ocean, a numerical validation was carried out at coastal, nearshore, and bay sites using several datasets from in-situ field campaigns. Good agreement was found between model and data in the coastal zone regarding to bottom and surface current, sea surface height and mean wave parameters. Vertical profiles of current were also well simulated, especially their modulation by ocean waves. The nearshore simulations reproduced the wave set-up and wave set-down, as well as the cross-shore dynamics with simulated undertow and streaming, and the longshore dynamics showing the longshore current generated by oblique incident ocean waves. Inside the bay, a modulation of the tidal wave is observed, as expected. The water filling and draining of the bay are well represented and follow the tidal phase: the ebb flow drains the bay while the flood flow fills it. These simulations were performed under calm and storm conditions, enabling us to identify the contribution of ocean waves to the hydrodynamics. The next step is to build the hydro-sedimentary model to assess the impact of hydrodynamics on sediment transport and the morphodynamics of the bay