Genetic Relations Between the Aves Ridge and the Grenada Back-Arc Basin, East Caribbean Sea

The Grenada Basin separates the active Lesser Antilles Arc from the Aves Ridge, described as a Cretaceous‐Paleocene remnant of the “Great Arc of the Caribbean.” Although various tectonic models have been proposed for the opening of the Grenada Basin, the data on which they rely are insufficient to reach definitive conclusions. This study presents, a large set of deep‐penetrating multichannel seismic reflection data and dredge samples acquired during the GARANTI cruise in 2017. By combining them with published data including seismic reflection data, wide‐angle seismic data, well data and dredges, we refine the understanding of the basement structure, depositional history, tectonic deformation and vertical motions of the Grenada Basin and its margins as follows: (1) rifting occurred during the late Paleocene‐early Eocene in a NW‐SE direction and led to seafloor spreading during the middle Eocene; (2) this newly formed oceanic crust now extends across the eastern Grenada Basin between the latitude of Grenada and Martinique; (3) asymmetrical pre‐Miocene depocenters support the hypothesis that the southern Grenada Basin originally extended beneath the present‐day southern Lesser Antilles Arc and probably partly into the present‐day forearc before the late Oligocene‐Miocene rise of the Lesser Antilles Arc; and (4) the Aves Ridge has subsided along with the Grenada Basin since at least the middle Eocene, with a general subsidence slowdown or even an uplift during the late Oligocene, and a sharp acceleration on its southeastern flank during the late Miocene. Until this acceleration of subsidence, several bathymetric highs remained shallow enough to develop carbonate platforms

Water column distribution of zooplanktonic size classes derived from in-situ plankton profilers: Potential use to contextualize contaminant loads in plankton

Pollution is one of the main anthropogenic threats to marine ecosystems. Studies analysing the accumulation and transfer of contaminants in planktonic food webs tend to rely on samples collected in discrete water bodies. Here, we assessed the representativeness of measurements at the chlorophyll-a maximum layer during the MERITE-HIPPOCAMPE cruise for the entire water column by investigating the vertical distribution of particles and plankton obtained by in-situ optical profilers at nine stations across the Mediterranean Sea. We identified specific conditions where the interpretation of results from contaminant analyses can be improved by detailing plankton size structure and vertical distributions. First, the presence of higher than usual plankton concentrations can result in sampling issues that will affect biomass estimation within each size class and therefore bias our understanding of the contaminant dynamics. Secondly, the presence of an unsampled water layer with high zooplankton biomass might imply non-resolved contaminant pathways along the trophic structure. This study lays the basis for optimizing sampling strategy in contaminant studies

Marine habitat classification: a pluridisciplinary approach in a high macrotidal environment - The case of the English median Channel

In megatidal sea, benthic marine communities are strongly dependent on the substrate, which is fashioned by hydrodynamism. This interdependence between substrate and benthic communities has enabled the establishment of marine benthic habitats classifications. Such classification allows depicting at the same time the general habitats diversity at the scale of a given shelf, and the local variations at the scale of a smaller area. Indeed, it meets diverse needs for ecological description of the marine environment such as general habitat knowledge or environmental impact assessment. The EUNIS classification is available to describe the main habitats of the European marine seabeds (Davies et al., 2004). Based on available data at the time of its delivery, it is well adapted to describe shallow bays and estuarine environments, mostly characterised by mobile muddy fine sediments. On the contrary it fails in describing correctly clean coarser sediments habitats in more deep areas such as those found in the central part of English Channel (La Manche) (Connor, 2005; James et al., 2007). This continental shelf sea connects with the Atlantic Ocean in its western part and to the Southern North Sea in its eastern part. It is characterised by a series of strong offshore-inshore and capes/bays gradients characterised by progressive changes in temperature, bathymetry, shear stress that are registered in the sediment, but also in the benthic communities

Benthic habitat diversity in coarse sediment under high macrotidal environment

EUNIS (European Nature Information System) is the habitat typology of reference in Europe but it must be implemented by new observations, particularly for the more detailed levels of the classification in coarse sediments which were historically less explored because of sampling difficulties. Two surveys in 2010 and 2011 permitted to sample twelve rectangular areas in the mid part of the Channel dominated by coarse sediment habitats in a high hydrodynamic environment strongly influenced by tidal currents (see Trentesaux et al., this conference for the map). During the survey, four longitudinal side-scan sonar (SSS) profiles were realised (~10 nm length) in each area allowing a real time selection of sampling areas. A minimum of four 0.25 m² Hamon grab sampling stations for quantitative macrofaunal and sediment analysis and two video footages (ROV Seabotix LBV200) were selected in each area (see figure). The main objectives of this study were to re-assess the EUNIS typology along an east-west gradient in the English Channel, and to find a way to integrate acoustic information in the description and mapping of the habitats which is not yet taken into account

Benthic habitat diversity in coarse sediment under high macrotidal environment

EUNIS (European Nature Information System) is the habitat typology of reference in Europe but it must be implemented by new observations, particularly for the more detailed levels of the classification in coarse sediments which were historically less explored because of sampling difficulties. Two surveys in 2010 and 2011 permitted to sample twelve rectangular areas in the mid part of the Channel dominated by coarse sediment habitats in a high hydrodynamic environment strongly influenced by tidal currents (see Trentesaux et al., this conference for the map). During the survey, four longitudinal side-scan sonar (SSS) profiles were realised (~10 nm length) in each area allowing a real time selection of sampling areas. A minimum of four 0.25 m² Hamon grab sampling stations for quantitative macrofaunal and sediment analysis and two video footages (ROV Seabotix LBV200) were selected in each area (see figure). The main objectives of this study were to re-assess the EUNIS typology along an east-west gradient in the English Channel, and to find a way to integrate acoustic information in the description and mapping of the habitats which is not yet taken into account

Marine habitat classification: a pluridisciplinary approach in a high macrotidal environment - The case of the English median Channel

In megatidal sea, benthic marine communities are strongly dependent on the substrate, which is fashioned by hydrodynamism. This interdependence between substrate and benthic communities has enabled the establishment of marine benthic habitats classifications. Such classification allows depicting at the same time the general habitats diversity at the scale of a given shelf, and the local variations at the scale of a smaller area. Indeed, it meets diverse needs for ecological description of the marine environment such as general habitat knowledge or environmental impact assessment. The EUNIS classification is available to describe the main habitats of the European marine seabeds (Davies et al., 2004). Based on available data at the time of its delivery, it is well adapted to describe shallow bays and estuarine environments, mostly characterised by mobile muddy fine sediments. On the contrary it fails in describing correctly clean coarser sediments habitats in more deep areas such as those found in the central part of English Channel (La Manche) (Connor, 2005; James et al., 2007). This continental shelf sea connects with the Atlantic Ocean in its western part and to the Southern North Sea in its eastern part. It is characterised by a series of strong offshore-inshore and capes/bays gradients characterised by progressive changes in temperature, bathymetry, shear stress that are registered in the sediment, but also in the benthic communities

Azimuthal anisotropy in the wider Vienna basin region: a proxy for the present-day stress field and deformation

International audienc

Coda-Q in the 2.5-20 s period band from seismic noise : application to the greater Alpine area

Coda-Q is used to estimate the attenuation and scattering properties of the Earth. So far focus has been on earthquake data at frequencies above 1 Hz, as the high noise level in the first and second microseismic peak, and possibly lower scattering coefficient, hinder stable measurements at lower frequencies. In this work, we measure and map coda-Q in the period bands 2.5-5 s, 5-10 s and 10-20 s in the greater Alpine region using noise cross-correlations between station pairs, based on data from permanent seismic stations and from the temporary AlpArray experiment. The observed coda-Q for short interstation distances is independent of azimuth so there is no indication of influence of the directivity of the incoming noise field on our measurements. In the 2.5-5 s and 5-10 s period bands, our measurements are self-consistent, and we observe stable geographic patterns of low and high coda-Q in the period bands 2.5-5 s and 5-10 s. In the period band 10-20 s, the dispersion of our measurements increases and geographic patterns become speculative. The coda-Q maps show that major features are observed with high resolution, with a very good geographical resolution of for example low coda-Q in the Po Plain. There is a sharp contrast between the Po Plain and the Alps and Apennines where coda-Q is high, with the exception a small area in the Swiss Alps which may be contaminated by the low coda-Q of the Po Plain. The coda of the correlations is too short to make independent measurements at different times within the coda, so we cannot distinguish between intrinsic and scattering Q. Measurements on more severely selected data sets and longer time-series result in identical geographical patterns but lower numerical values. Therefore, high coda-Q values may be overestimated, but the geographic distribution between high and low coda-Q areas is respected. Our results demonstrate that noise correlations are a promising tool for extending coda-Q measurements to frequencies lower than those analysed with earthquake data

The AlpArray Seismic Network: A Large-Scale European Experiment to Image the Alpine Orogen

The AlpArray programme is a multinational, European consortium to advance our understanding of orogenesis and its relationship to mantle dynamics, plate reorganizations, surface processes and seismic hazard in the Alps-Apennines-Carpathians-Dinarides orogenic system. The AlpArray Seismic Network has been deployed with contributions from 36 institutions from 11 countries to map physical properties of the lithosphere and asthenosphere in 3D and thus to obtain new, high-resolution geophysical images of structures from the surface down to the base of the mantle transition zone. With over 600 broadband stations operated for 2 years, this seismic experiment is one of the largest simultaneously operated seismological networks in the academic domain, employing hexagonal coverage with station spacing at less than 52 km. This dense and regularly spaced experiment is made possible by the coordinated coeval deployment of temporary stations from numerous national pools, including ocean-bottom seismometers, which were funded by different national agencies. They combine with permanent networks, which also required the cooperation of many different operators. Together these stations ultimately fill coverage gaps. Following a short overview of previous large-scale seismological experiments in the Alpine region, we here present the goals, construction, deployment, characteristics and data management of the AlpArray Seismic Network, which will provide data that is expected to be unprecedented in quality to image the complex Alpine mountains at depth