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International audience; A new conodont species, Siphonodella leiosa, is described from the lower Carboniferous pelagic limestones of the Montagne Noire (France), deposited in North Gondwana on a outer platform environment. Specimens were obtained from one level dated to the Siphonodella jii conodont Zone. The major difference from other siphonodellid conodonts known in this area is that the elements of this new species have a practically entirely smooth and unornamented platform, apart from the development of one or two low rostral ridge-like nodes. Similar morphologies were generally observed in shallow marine deposits of the same time frame from China, Russia and East and Central European areas. The new discovery reinforces the idea that ornamentation of siphonodellids is not only related to bathymetry, but that temperature could play an important role in the diversification and radiation of unornamented species during the Siphonodella jii conodont Zone.

A quantitative sampling was made on the non-cultivated molluscs of the soft bottom macrofauna in the bay of Marennes-Oleron. A stratified random sampling, including an optimal allocation strategy. provided adequate data to estimate abundance and biomass (total weight. dry weight and ash-free-dry weight) of each molluscan species. The main stratification factors were respectively the bathymetric levels. the different types of sediment and the differences between natural, oyster-free mud flats and cultivated areas. A Smith Mc-Intyre grab was used to sample the subtidal, shallow areas and the tidal flats as well. The total number of sampling stations was 370. The final estimation of the total weight of benthic molluscs was 14,400 ± 3,000 tons (at 95 % confidence limits). The main trophic competitors for oysters were : Cerastoderma edule (4,500 ± 2,200 tons), Mytilus edulis (2,600 ±. 2,000 tons), Crepidula fornicata (1,800 ±. 900 tons), Solen marginatus (800 ±. 600 tons) and Macoma balthica (800 ± 400 tons). La stratégie d'échantillonnage retenue pour l'estimation des stocks de mollusques benthiques non cultivés du bassin de Marennes-Oléron consiste en un type d'échantillonnage aléatoire stratifié, après allocation optimale de l'effort d'échantillonnage au sein des strates. L'engin de prélèvement, une benne Smith Mc-Intyre, a été utilisée sur l'ensemble de la zone soit 180 km. Les principaux stratificateurs sont la bathymétrie, les types biosédimentaires et la présence ou l'absence de culture d'huîtres. Un ensemble de 370 stations a été effectué. Le stock global de mollusques non cultivés est évalué en biomasse fraîche à 14 400 ± 3 000 tonnes (au seuil d'erreur de 5 %). Les principales espèces compétitrices sur le plan trophique des huîtres sont : Cerastoderma edule (4 500 ± 2 000 tonnes), Mytilus edulis (2 600 ±. 2 000 tonnes), Crepidula fornicata (1 800 ± 900 tonnes), Solen marginatus (800 ± 600 tonnes) et Macoma balthica (800 ±. 400 tonnes).

Abstract Over the years, hurricane track forecasts and storm surge models, as well the digital terrain and bathymetry data they depend on, have improved significantly. Strides have also been made in the knowledge of the detailed variation of the surface wind field driving the surge. The area of least improvement has been in obtaining data on the temporal/spatial evolution of the mound of water that the hurricane wind and waves push against the shore to evaluate the performance of the numerical models. Tide gauges in the vicinity of the landfall are frequently destroyed by the surge. Survey crews dispatched after the event provide no temporal information and only indirect indications of the maximum water level over land. The landfall of Hurricane Bonnie on 26 August 1998, with a surge less than 2 m, provided an excellent opportunity to demonstrate the potential benefits of direct airborne measurement of the temporal/spatial evolution of the water level over a large area. Despite a 160-m variation in aircraft altitude, an 11.5-m variation in the elevation of the mean sea surface relative to the ellipsoid over the flight track, and the tidal variation over the 5-h data acquisition interval, a survey-quality global positioning system (GPS) aircraft trajectory allowed the NASA scanning radar altimeter carried by a NOAA hurricane research aircraft to demonstrate that an airborne wide-swath radar altimeter could produce targeted measurements of storm surge that would provide an absolute standard for assessing the accuracy of numerical storm surge models.

Lake Afdera is a hypersaline endorheic lake situated at 112 m below sea-level in the Danakil Depression. The Danakil Depression is located in the northern part of the Ethiopian Afar and features an advanced stage of continental rifting. The remoteness and inhospitable environment explain the limited scientific research and knowledge about this lake. Bathymetric data were acquired during 2 weeks expeditions in January/February 2016 and 2017 using an easily deployable echosounder system mounted on an inflatable motorized boat. This study presents the first complete bathymetric map of the lake Afdera. Bathymetric results show that the lake has an average depth of 20.9 m and a total volume of 2.4 km3. The maximum measured depth is 80 m, making Lake Afdera the deepest known lake in Afar and the lowest elevation of the Danakil Depression. Comparison with historical reports shows that the lake level did not fluctuate significantly during the last 50 years. Two distinct tectonic basins to the north and the south are recognized. Faults of different orientations control the morphology of the northern basin. In contrast, the southern basin is affected by volcano-tectonic processes, unveiling a large submerged caldera. Comparison between the orientation of faults throughout the lake with the regional fault pattern indicates that the lake is part of two transfer zones: the major Alayta–Afdera Transfer Zone and the smaller Erta Ale–Tat’Ali Transfer Zone. The interaction between these Transfer Zones and the rift axis forms the equivalent of a developing nodal basin which explains the lake’s position as the deepest point of the depression. This study provides evidence for the development of an incipient transform fault on the floor of the Afar depression.

Currently, due to the global change and biodiversity loss, the knowledge of the species taxonomy and distribution is more than ever crucial. Especially in areas as the Avilés canyon systems (ACS), which is a Site of Community Importance (SCI) included in the Natura 2000 Network. A check-list of the echinoderm species belonging to the class Holothuroidea (a group that has been less studied and with scarce literature available) from the ACS was carried out, as well as a characterization of the holothurian fauna and its distribution. Samples were collected from both the continental shelf, slope and bathyal zones of the Asturian central coast (COCACE cruise, 1987–88), and the slope, bathyal and abyssal areas of the Avilés canyon systems (BIOCANT cruises, 2012–13). The identification of the species was based on morphological traits as well as on the observation of the microscopic calcareous ossicles extracted from different parts of the holothurian body. One hundred and seventy four specimens, belonging to 35 species of the five orders of the class Holothuroidea, were identified. Multivariate analysis allowed the differentiation of four main assemblages, which corresponded to abyssal plain, lower continental slope, upper continental slope, and continental shelf. Depth was the main structuring agent. Holothurian species richness was higher in deep-sea areas, the abyssal plain being the area with the highest number of species found.

International audience; A unique late Glacial–Preboreal record of changes in sea-level and sediment fluxes originating from the Alps is recorded in the Rhône subaqueous delta in the Western Mediterranean Sea. The compilation of detailed bathymetric charts, together with high-resolution seismic profiles and long cores, reveals the detailed architecture of several sediment lobes, related to periods of decreased sea-level rise and/or increased sediment flux. They are situated along the retreat path of the Rhône distributaries, from the shelf edge and canyon heads up to the modern coastline. They form transgressive backstepping parasequences across the shelf, the late Holocene (highstand) deltas being confined to the inner shelf. The most prominent feature is an elongated paleo-shoreface/deltaic system, with an uppermost sandy fraction remolded into subaqueous dunes. A long piston core into the bottomsets of this prograding unit allows precise dating of this ancient deltaic system. In seismic data, it displays aggradation, starting at not, vert, similar 15 cal kyr BP, followed by progradation initiated during the first phase of the Younger Dryas, a period of reduced sea-level rise or stillstand. The delta kept pace with resumed sea-level rise during the Preboreal (which is estimated at about 1 cm/yr), as a result of increased sediment supply from the Alps (melting of glaciers and more humid climate “flushing” the sediment down to the sea). Abandonment of the delta occurred around 10,500 cal yr BP, that is to say about 1000 yr after the end of the Younger Dryas, probably because of decreased sediment flux.

Co-auteur étranger; International audience; Deep-sea submarine eruptions are the least known type of volcanic activity, due to the difficulty of detecting, monitoring, and sampling them. Following an intense seismic crisis in May 2018, a large submarine effusive eruption offshore the island of Mayotte (Indian Ocean) has extruded at least 6.5 km3 of magma to date, making it the largest monitored submarine eruption as well as the largest effusive eruption on Earth since Iceland's 1783 Laki eruption. This volcano is located along a WNW-ESE volcanic ridge, extending from the island of Petite Terre (east side of Mayotte) to about 3,500 m of water depth. We present a detailed petrological and geochemical description of the erupted lavas sampled by the MAYOBS 1, 2, and 4 cruises between May and July 2019 and use these to infer characteristics and changes through time for the whole magmatic system and its dynamics from the source to the surface. These cruises provide an exceptional time-series of bathymetric, textural, petrological, and geochemical data for the 2018-2019 eruptive period, and hence bring an invaluable opportunity to better constrain the evolution of magma storage and transfer processes during a long-lived submarine eruption. Integrating the petrological signatures of dredged lavas with geophysical data, we show that the crystal-poor and gas-rich evolved basanitic magma was stored at mantle depth (>37 km) in a large (≥10 km3) reservoir and that the eruption was tectonically triggered. As the eruption proceeded, a decrease in ascent rate and/or a pathway change resulted in the incorporation of preexisting differentiated magma stored at a shallower level. Magma transfer from the deep mantle reservoir is syn-eruptive, as indicated by transfer times estimated from diffusion in zoned olivine crystals that are much shorter than the total eruption duration. Our petrological model has important hazard implications concerning the rapid and stealthy awakening of a deep gas-rich magma reservoirs that can produce unusually high output rates and long-lived eruption. Sudden tapping of large crystal poor reservoirs may be the trigger mechanism for other rarely witnessed high-volume (>1 km3) effusive events.

Wave height variability along the crest of breaking waves is shown to be a significant factor in the assessment of surf zone dynamics. Variations in excess of 50 percent of the maximum wave height can occur along a single crest without significant variations in bathymetry. The horizontal scale of this longshore variability in crest height corresponds to the wave length of incident breaking waves. Four possible mechanisms for this variability are postulated and then evaluated individually on the basis of field observations. A major result of these evaluations is that two-dimensional shallow-water wave equations appear to be inappropriate for expressing natural surf zone wave transformations and water motions even under the condition of waves encroaching on a plane sloping bottom. Consequently, three-dimensional equations of surf should be used for describing most natural surf zone dynamics.