Contourite distribution and bottom currents in the NW Mediterranean Sea: Coupling seafloor geomorphology and hydrodynamic modelling

Contourites are common morphological features along continental margins where currents encounter the seafloor. They can provide long-term archives of palaeoceanography, may be prone to sediment instability, and can have a great potential for hydrocarbon exploration. Despite their importance and increasingly recognised ubiquitous occurrence worldwide, the link between oceanographic processes and contourite features is poorly constrained. In particular, it is unclear under which specific conditions sediments are mobilised, modified and deposited by bottom currents. Here, we aim to determine key bottom current characteristics (velocity and bottom shear stress) affecting contourite deposition, by assuming that recent oceanographic regimes may be extended back in time over the past glacial-interglacial cycles, with strong winter circulation assumed similar to glacial conditions and weak summer circulation to interglacials. We present an integrated study from the NW Mediterranean Sea that couples results of the MARS3D hydrodynamic model with high-resolution sedimentological and geophysical data (piston cores, multibeam bathymetry and high resolution seismic data). Near bottom circulation was modelled during winter and summer 2013 as representative of past periods of high and low current intensity, respectively. Model results match well with the extent of contourite depositional systems and their different localised morphologic elements. We deduce that higher intensity events control the formation of erosional features such as moats and abraded surfaces. The heterogeneous distribution of bottom-current intensity on slopes explains the development of different types of contourite drifts. Plastered drifts form in zones of low bottom-current velocities constrained upslope and downslope by higher current velocities. Separated elongated mounded drifts develop where fast bottom-currents decelerate at foot of the slope. In contrast, no mounded contourite morphologies develop when the current velocity is homogeneous across the slope, especially in margins prone to downslope sediment transport processes. In confined basins, gyres may transport sediment in suspension from a margin with a high sediment supply to an adjacent starved margin, favouring the development of fine-grained contourites in the latter. Our results provide new insights into how detailed bottom-circulation modelling and seafloor geomorphological analyses can improve the understanding of palaeoflow-regimes, at least over time spans when the overall paleogeography and the distribution of contourite drifts is comparable to present-day conditions. The approach of coupled hydrodynamic models and geomorphological interpretations proposed here for depositional, erosional and mixed contourite features may be used to understand other areas affected by bottom currents, and for a better conceptual understanding of bottom-current processes and their interactions with the seafloor

Bone Marrow Transplant

Mucopolysaccharidosis type I-H (MPS I-H) is a rare lysosomal storage disorder caused by α-L-Iduronidase deficiency. Early haematopoietic stem cell transplantation (HSCT) is the sole available therapeutic option to preserve neurocognitive functions. We report long-term follow-up (median 9 years, interquartile range 8-16.5) for 51 MPS I-H patients who underwent HSCT between 1986 and 2018 in France. 4 patients died from complications of HSCT and one from disease progression. Complete chimerism and normal α-L-Iduronidase activity were obtained in 84% and 71% of patients respectively. No difference of outcomes was observed between bone marrow and cord blood stem cell sources. All patients acquired independent walking and 91% and 78% acquired intelligible language or reading and writing. Intelligence Quotient evaluation (n = 23) showed that 69% had IQ ≥ 70 at last follow-up. 58% of patients had normal or remedial schooling and 62% of the 13 adults had good socio-professional insertion. Skeletal dysplasia as well as vision and hearing impairments progressed despite HSCT, with significant disability. These results provide a long-term assessment of HSCT efficacy in MPS I-H and could be useful in the evaluation of novel promising treatments such as gene therapy

A ten-year numerical hindcast of hydrodynamics and sediment dynamics in the Loire Estuary

Abstract A numerical hindcast of the macrotidal Loire Estuary (France) has been generated to provide a long-term dataset (2008–2018) of estuarine hydrodynamics, temperature, salinity, and sediment dynamics. This hindcast is based on simulations coupling water motion, wave and mixed sediment models, forced with realistic conditions and extensively validated in the salinity gradient and turbidity maximum areas. These data represent extremely valuable information for diverse scientific communities, providing (i) environmental parameters for ecosystemic studies along the Loire River–sea continuum, (ii) a singular estuarine configuration for inter-comparison of estuarine functioning, and (iii) a ten-year synoptical view of a major estuarine environment of the North Atlantic Ocean

Brittany’s infralittoral seabed: an objective partitioning into marine ecological units

Marine biological distribution patterns are largely regulated by the physico-chemical properties of the overlying waters. The availability of new environmental layers with sub-kilometric resolution is therefore of great use to map marine in objective ways and therefrom interpret biogeographic patterns, optimize region-wide field surveys or plan in situ experiments. This report presents a data-driven high-resolution partitioning of Brittany’s infralittoral seabed environment areas with comparable environmental conditions. Six major abiotic drivers of shallow-water biological communities are used to compose its environmental space, notably: temperature, salinity, oxygen, light, wave-induced kinetic energy and baroclinic currents kinetic energy. Each parameter is represented in the analysis by a climatologic raster corresponding to average conditions at seabed computed from multiannual series extracted from latest generation oceanographic models and satellite imagery. A k-means unsupervised partitioning, assisted by an optimal cluster number estimation, is used to statistically partition the points representing the environmental space, which are exclusively described by their environmental attributes. Mapping of the clustered data depicts spatially-coherent areas that match ecological divisions traditionally-recognised in Brittany by experts but which previously lacked a fine and objective spatial delimitation. The divide between northern and southern Brittany is successfully demarcated as well as specific ecological conditions associated to (i) bays, (ii) areas influenced by freshwater outflows, (iii) swell-exposed coastal stretches and (iv) current-exposed sectors. The analysis further highlights small ecological enclaves geographically isolated from their larger analogues. By representing conditions at seabed in great detail, the result permits a better understanding of the benthic compartment than previous analyses based on surface and/or vertically-integrated conditions. The approaches success demonstrates the capacity to analyse and exploit Ifremer wealth of novel environmental datasets to objectively map marine ecological units.Les patrons de distribution des espèces et communautés marines sont largement régulés par les propriétés physico-chimiques des eaux environnantes. La mise à disposition de nouvelles couches environnementales à résolution sub-kilométrique s’avère, par conséquent, d’une grande utilité pour cartographier de façon objective les paysages écologiques marins en vue d’interpréter des patrons biogéographiques, optimiser les campagnes à la mer ou planifier de manière adéquate les expérimentations in situ. Le présent rapport a pour objet la segmentation à haute résolution des fonds marins infralittoraux de la Bretagne en zones aux conditions environnementales analogues. Six facteurs abiotiques majeurs régissant la distribution spatiale des communautés biologiques infralittorales sont utilisés pour composer l’espace environnemental, à savoir : la température, la salinité, l’oxygène, la lumière, l’énergie cinétique due aux vagues et l’énergie cinétique induite par les courants. Chaque facteur se présente dans l’analyse sous la forme d’un raster climatologique caractérisant les conditions moyennes au fond calculées à partir de séries pluriannuelles issues des modèles océanographiques ou de l’imagerie satellitaire de dernière génération. Un partitionnement non-supervisé par la méthode des k-médoïdes, assistée par une estimation du nombre optimal de clusters, est utilisé pour regrouper statistiquement les points représentant l’espace environnemental, décrits uniquement par leurs attributs environnementaux. Le résultat met en évidence une série de zones benthiques écologiquement similaires qui sont en accord avec les patrons écologiques connus en Bretagne par les experts, mais dont les contours étaient flous. La démarcation Nord/Sud en Bretagne est ainsi bien capturée, de même que d’autres unités écologiques particulières telles que (i) les baies, (ii) les zones à influence estuarienne, (iii) les zones côtières exposées aux vagues, et (iv) les secteurs exposés aux courant. L’analyse met aussi en évidence des petites enclaves écologiques isolées géographiquement de leurs analogues plus étendus. Grâce à une bonne représentation des conditions aux abords des fonds marins, le résultat permet de meilleures interprétations du compartiment benthique que les résultats issus des analyses précédentes qui utilisaient des conditions de surface ou moyennées verticalement sur la colonne d’eau. Le succès de l’approche démontre la capacité à analyser et à valoriser une grande quantité de données environnementales originales produites à l’Ifremer pour cartographier avec plus de détail les paysages écologiques marins

Using two-way nesting technique AGRIF with MARS3D V11.2 to improve hydrodynamics and estimate environmental indicators

Abstract. In the ocean, meso / submesoscale structures and coastal processes are associated with fine scales. The simulation of such features thus requires the hydrodynamic equations to be solved at high-resolution (from a few hundred meters down to a few tens of meters). Therefore, local mesh refinement is a primary issue for regional and coastal modelling. As over structured grids, AGRIF (Adaptive Grid Refinement In Fortran) library is committed to tackle this challenge. It has been implemented in MARS3D, which is a numerical model developed by Ifremer (the French research institute for the exploitation of the sea) for coastal environmental researches and studies. The present paper describes how the dedicated implementation preserves some essential principles (mass conservation, constant preserving…) along with the induced constraints. The use and the performance of this new tool are detailed over two configurations that illustrate the wide range of scales and resolutions typically targeted by coastal applications. The first one is based on multiple high-resolution (500 m) grids that pave the coastal ocean over thousands of kilometres, allowing a continuum between the regional and coastal scales. The second application is more local and has a finer resolution (50 m). It targets a recurrent question for semi-enclosed bays: the renewal time indicator. Throughout these configurations, the paper intends at comparing the two-way nesting method with the traditional one-way approach and highlights how MARS3D-AGRIF tool proves to be an efficient way significantly improve the physical hydrodynamics and bring it biological issues

Potential and limitations of convection-permitting CNRM-AROME climate modelling in the French Alps

International audienceConvection-permitting climate modelling is a promising avenue for climate change research and services especially in mountainous regions. Work is required to evaluate the results of high-resolution simulations against relevant observations, and put them in a broader context against coarser resolution modelling frameworks. Here we evaluate numerical simulations with the convection-permitting regional climate model CNRM-AROME ran at 2.5 km horizontal resolution over a large pan-Alpine domain in the European Alps, using either the ERA-Interim or climate model output as boundary conditions. This study analyses annual and seasonal characteristics of 2 m temperature, total precipitation, solid fraction of precipitation and snow depth at the scale of the French Alps under past and future climate conditions. The results are compared with the local reanalysis S2M, and raw or adjusted, with the ADAMONT method, simulations of the regional climate model CNRM-ALADIN driven either by the ERA-Interim reanalysis or the CNRM-CM5 global climate model. The study highlights generally similar differences in past and future climate between the datasets, as well as obstacles to the use of some CNRM-AROME outputs as they stand. These consist of excessive accumulation of snow on the ground above 1,800 m a.s.l., as well as lower temperature values at same elevations than the S2M reanalysis and the ADAMONT-adjusted outputs. Besides these obstacles, CNRM-AROME simulations present several advantages compared to the raw CNRM-ALADIN outputs. Among them, a significantly smaller cold bias, more realistic values of accumulated precipitations, as well as a better representation of the spatial variability of the different variables investigated, which always stand closer to the reference data than in the CNRM-ALADIN outputs. As suggested by many studies, CNRM-AROME could even produce more realistic accumulated precipitations at high elevation than the S2M reanalysis taken as our reference and consequently than the ADAMONT-adjusted projections, but the lack of a reliable set of high-resolution observations at high elevation remains an obstacle to their evaluation

Numerical modeling of bedload and suspended load contributions to morphological evolution of the Seine Estuary (France)

This numerical modeling study (i) assesses the influence of the sediment erosion process on the sediment dynamics and subsequent morphological changes of a mixed-sediment environment, the macrotidal Seine estuary, when non-cohesive particles are dominant within bed mixtures (non-cohesive regime), and (ii) investigates respective contributions of bedload and suspended load in these dynamics. A three dimensional (3D) process-based morphodynamic model was set up and run under realistic forcings (including tide, waves, wind, and river discharge) during a 1-year period. Applying erosion homogeneously to bed sediment in the non-cohesive regime, i.e., average erosion parameters in the erosion law (especially the erodibility parameter, E0), leads to higher resuspension of fine sediment due to the presence of coarser fractions within mixtures, compared to the case of an independent treatment of erosion for each sediment class. This results in more pronounced horizontal sediment flux (two-fold increase for sand, +30% for mud) and erosion/deposition patterns (up to a two-fold increase in erosion over shoals, generally associated with some coarsening of bed sediment). Compared to observed bathymetric changes, more relevant erosion/deposition patterns are derived from the model when independent resuspension fluxes are considered in the non-cohesive regime. These results suggest that this kind of approach may be more relevant when local grain-size distributions become heterogeneous and multimodal for non-cohesive particles. Bedload transport appears to be a non-dominant but significant contributor to the sediment dynamics of the Seine Estuary mouth. The residual bedload flux represents, on average, between 17 and 38% of the suspended sand flux, its contribution generally increasing when bed sediment becomes coarser (can become dominant at specific locations). The average orientation of residual fluxes and erosion/deposition patterns caused by bedload generally follow those resulting from suspended sediment dynamics. Sediment mass budgets cumulated over the simulated year reveal a relative contribution of bedload to total mass budgets around 25% over large erosion areas of shoals, which can even become higher in sedimentation zones. However, bedload-induced dynamics can locally differ from the dynamics related to suspended load, resulting in specific residual transport, erosion/deposition patterns, and changes in seabed nature

Accumulation and dispersion dynamics of mud and sand particles in a continental shelf under estuarine influence: a numerical modelling analysis (Gironde, France)

Coastal environments are directly influenced by terrigenous inputs coming from rivers through estuaries. Quantifying the amount of nutrients and contaminants brought by sediments from continental areas to the sea is of major interest for marine resource protection. The complexity of the intra-estuarine dynamics, associated with the strong variability of meteorological forcing makes it difficult to quantify the residence time of particles within the estuary and the accumulation and dispersion areas offshore the mouth. Moreover, the dynamics of fine sediment trapping areas in the adjacent continental shelf (e.g. temporary or permanent storage such as the “West-Gironde Mud Patch” (WGMP) ) remains extremely challenging to address. Based on a realistic process-based numerical model, the aim of this work is to investigate the dynamics of the sediment accumulation and dispersion areas in order: (i) to describe the role played by the intertidal mudflats and the subtidal mud patches on sediment trapping and further resuspension, and (ii) to investigate the influence of hydro-meteorological events (e.g. high/low river discharges, storms) on sediment fluxes

Impact hydrodynamique de la mise en place d’un parc d’hydroliennes en Baie du Mont Saint-Michel

Les fortes vitesses rencontrées à l’entrée de la Baie du Mont Saint-Michel font de cet environnement macro-tidal un endroit privilégié, en termes de ressources énergétiques, pour l’implantation d’une ferme d’hydroliennes. Afin d’établir plus précisément son potentiel énergétique et d’évaluer l’impact de l’implantation de telles machines sur son hydrodynamisme, une modélisation hydrodynamique de la Baie du Mont Saint-Michel est mise en oeuvre à l’aide du modèle de circulation régionale MARS3D (LAZURE & DUMAS, 2008) dans sa version tridimensionnelle. La validation hydrodynamique de cette configuration est réalisée à partir de comparaisons à des mesures courantologiques récentes (KERVELLA, 2010). A partir de cette modélisation, une cartographie du potentiel énergétique de la Baie est établie et les endroits propices à l’installation de structures récupératrices de l’énergie des courants sont identifiés. L’impact de l’implantation d’une ou plusieurs structures à l’un de ces endroits sur l’hydrodynamique de la Baie est évalué : l’effet de l’extraction d’énergie des courants est modélisé par l’implémentation d’un nouveau terme puits, correspondant à une force de retard colinéaire à l’écoulement (DEFNE et al., 2011), dans les équations du mouvement de MARS3D. Les résultats présentés pour 2 valeurs d’extraction de l’énergie disponible (25% et 55%) montrent que l’impact d’un parc de petite superficie sur les courants reste très local

Contourite identification along Italian margins: The case of the Portofino drift (Ligurian Sea)

A brief review of the published evidence of current deposits around Italy is the occasion to test the robustness of matching bottom current velocity models and seafloor morphologies to identify contourite drifts not yet documented. We present the result of the regional hydrodynamic model MARS3D in the Northern Tyrrhenian and Ligurian Sea with horizontal resolution of 1.2 km and 60 levels with focus on bottom current: data are integrated over summer and winter 2013 as representative of low and high intensity current conditions. The Eastern Ligurian margin is impacted by the Levantine Intermediate Water (LIW) with modeled mean velocity of bottom current up to 20 cm s−1 in winter 2013 and calculated bottom shear stress exceeding 0.2 N m−2 in water depth of 400–800 m. By crossing this information with seafloor morphology and geometry of seismic reflections, we identify a sediment drift formerly overlooked at ca 1000 m water depth. The Portofino separated mounded drift has a maximum thickness of at least 150 m and occurs in an area of mean current velocity minimum. Independent evidence to support the interpretation include bottom current modelling, seafloor morphology, seismic reflection geometry and sediment core facies. The adjacent areas impacted by stronger bottom currents present features likely resulted from bottom current erosion such as a marine terrace and elongated pockmarks. Compared to former interpretation of seafloor morphology in the study area, our results have an impact on the assessment of marine geohazards: submarine landslides offshore Portofino are small in size and coexist with sediment erosion and preferential accumulation features (sediment drifts) originated by current-dominated sedimentary processes. Furthermore, our results propel a more general discussion about contourite identification in the Italian seas and possible implications