Enregistrements sédimentaires holocènes du plateau continental de la Baie d’Al Hoceima (Maroc) et lien avec les forçages tectoniques et climatiques.
Les plateaux continentaux sont au centre du continuum terre-mer et leur étude est déterminante pour comprendre l’évolution tectono-sédimentaire des bassins sédimentaires. Façonnés par les apports fluviatiles et la production bioclastique côtière, les plateaux continentaux sont sensibles aux variations du niveau marin relatif et aux changements climatiques.La baie d’Al Hoceima, au large du Maroc, sur la bordure Sud de la Mer d’Alboran offre la possibilité de caractériser la stratigraphie quaternaire de la plate-forme sud-méditerranéenne peu documentée. Cette région enregistre une forte sismicité liée au système de failles actives d’Al Idrissi qui engendre une subsidence de la baie. Plusieurs cycles à 100 000 ans sont enregistrés et permettent d’appréhender les variations tectoniques, climatiques et anthropiques de la région d’Al Hoceima depuis le Pléistocène supérieur.A partir de données de sismique Sparker (mission Malboro-2, 2012), de sondeur de sédiment Chirp et de 5 carottes Calypso (entre 5 m et 15 m de long), prélevées au centre de la baie (mission Albacore, 2021), notre étude propose une caractérisation sédimentologique et chronostratigraphique des sédiments holocènes. Elle met en évidence une surface d’érosion marine marquée par des débris coquilliers grossiers datant du dernier bas niveau marin (Last Glacial Maximum – LGM ). Elle est surmontée de prismes transgressifs (Transgressive System Tract – TST ) marquant le début de la remontée du niveau marin, suivis par des dépôts pro-deltaïques de haut niveau marin (Highstand System Tract – HST ).Une succession de prismes TST échelonnés depuis la plate-forme médiane jusqu’à la frange littorale est caractérisée par des géométries progradantes en direction du bassin à la faveur d’une paléotopographie complexe, héritée du LGM. L’unité pro-deltaïque HST montre plusieurs générations de sediment waves également visibles sur le fond marin actuel entre 50 et 100 de profondeur bathymétrique. Le caractère ondulé de ces dépôts est interprété comme une intensification des écoulements fluviatiles pouvant être le résultat d’une augmentation de la pluviométrie et/ou des changements de pratique agricole dans la région d’Al Hoceima.
(27/10/2025)
iSTeP, INSU - CNRS, SU, CNRS, CY, GEO-OCEAN, UBS, IFREMER, INSU - CNRS, UBO EPE, CNRS, SU FSI, SU, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
New insights on the regional architecture and dynamics of mixed fluvio-aeolian deposits from Middle Buntsandstein in the southern margin of the German Basin
(pp. 658920, 27/10/2025)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IFPEN, Bordeaux INP, GR, UR, INSU - CNRS, CNRS
Les glissements sous-marins du Cône de l'Amazone: caractérisation de leurs processus de mise en place
Les glissements sous-marins sont un « objet » sédimentaire communs à toutes les marges continentales. Ils résultent du déplacement gravitaire de blocs cohérents le long de surfaces de rupture. De par leur volume, ils modifient quasi-instantanément la morphologie et la physiographie des marges. Leur compréhension est essentielle pour évaluer les risques tsunamogènes, notamment dans un contexte de changement climatique et d’anthropisation croissante des littoraux qui affectent l’hydrodynamisme, la vitesse de sédimentation et la stabilité des pentes, et augmentent ainsi potentiellement la fréquence de ces phénomènes. Ce travail vise à comprendre les mécanismes de mise en place des dépôts de transport en masse (Mass-Transport Deposits – MTD) observés sur le haut de pente du Cône sous-marin de l’Amazone, en analysant leurs compositions et leurs organisations internes, en déterminant l’origine des sédiments mobilisés et en datant les épisodes de dépôt pour établir leur possible lien avec les variations climato-eustatiques. Ce travail s’inscrit dans le cadre du projet ANR MEGA. Il repose sur l’analyse de trois carottes et de données acoustiques haute résolution (profils Chirp) obtenues durant la campagne AMARYLLIS-AMAGAS (2023). Les analyses microgranulométriques, XRF, des cortèges argileux et des foraminifères benthiques indiquent que les sédiments remobilisés des MTD et les argiles hémipélagiques en place sont très similaires en termes de composition lithologique, de contenu micropaléontologique et de géochimie. Les datations 14C et les analyses biostratigraphiques ont permis d’identifier les périodes de déclenchement des MTD. Les images RX révèlent des structures de déformation dominées par des plissements de tailles variées, associés à du cisaillement, des rafts microfracturés, voire à des écoulements gravitaires de type débrite. Les MTD prendraient leur source vers 200 m de profondeur d’eau, avec des distances de déplacement variées, de quelques centaines de mètres à plusieurs dizaines de kilomètres, et parfois des mises en place polyphasées. Leur déclenchement serait lié aux variations climato- eustatiques du Dernier Maximum Glaciaire et de la déglaciation. Il serait causé soit par une surcharge sédimentaire liée à la forte augmentation des taux de sédimentation soit par la dissociation des hydrates de gaz causée par les variations de température des eaux de fond affectant le haut de pente
(27/10/2025)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, GEOAZUR 7329, INSU - CNRS, UniCA, CNRS, IRD [Occitanie], UniCA, LOG, INSU - CNRS, ULCO, CNRS, IRD [Ile-de-France]
Structures internes des dépôts de transport en masse du Cône sous-marin de l'Amazone : en quoi nous renseignent-elles sur les processus de mise en place des glissements sous-marins ?
Les glissements sous-marins sont un processus de premier ordre qui affecte et façonne les marges océaniques du monde entier, impliquant le transfert de volumes variables de sédiments. Les plus grands glissements connus (10 à 2000 km3) sont retrouvés sur les marges continentales passives, caractérisées par une faible activité sismique et de faibles pentes (généralement < 2◦). Malgré celles-ci, les masses remobilisées peuvent se déplacer sur plusieurs dizaines voire centaines de kilomètres. Afin de comprendre leurs mécanismes de mise en place, nous avons analysé huit carottes de type Calypso collectées sur le haut de la pente continentale du Cône sous-marin de l’Amazone, à environ 50 km en aval de la zone de déclenchement, pendant la campagne AMARYLLIS-AMAGAS I (2023). Les limites des dépôts de transport en masse (MTD) ont été définies par la reconnaissance de structures de déformation dans les carottes puis par corrélation avec les profils Chirp. Les déformations ont été identifiées à partir des descriptions visuelles, des photographies et/ou des images rX. Ce travail a été effectué dans le cadre du projet ANR MEGA. Cinq classes de déformation ont été définies. La classe 1 comprend des structures de boudinage et des "écailles" centimétriques imbriquées illustrant un intense cisaillement associé à un faible déplacement horizontal. La classe 2 correspond à des dépôts hémipélagiques basculés de 5-40◦ et fortement micro-fracturés. La classe 3 comprend des structures plissées de taille centimétrique/plurimétrique, impliquant une rhéologie visqueuse et une absorption d’énergie associée à une décélération du MTD. La classe 4 correspond à des dépôts hémipélagiques sub-horizontaux mais intensément micro-fracturés et interprétés comme des mégablocs encore non désintégrés. La classe 5 présente des clastes arrondis flottant dans une matrice argileuse qui caractérisent le faciès débrite et le plus fort degré de déformation. Au sein des MTD, un motif classique de déformations comprend la superposition de bas en haut des classes 1 à 4 ou celle des classes 5 et 4 ou 1, 5 et 4. Ces motifs pouvant être superposés plusieurs fois, les MTD résulteraient d’une mise en place par gel successif de leur partie basale ou de la superposition d’épisodes de rupture/glissement distincts.
(27/10/2025)
GEOAZUR 7329, INSU - CNRS, UniCA, CNRS, IRD [Occitanie], UniCA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, iSTeP, INSU - CNRS, SU, CNRS, CY, UERJ
Transient dynamics in confined aquifers: Planning horizon impacts on sustainable yield estimations
Confined aquifers challenge current groundwater sustainability concepts due to their long response time scales and the dampening potential of aquitards. Pumping introduces a perturbation that initiates a transient response, which propagates through the confining units towards adjacent aquifers and surface systems. As a result, the planning horizon, which refers to the timeframe over which management decisions are evaluated, becomes a critical factor in sustainability assessments. This work explores how sustainable yield estimations in confined systems are influenced by climatic conditions, the degree of confinement, and the chosen planning horizon. To investigate this, a synthetic cross-section model of a multi-layer aquifer system was developed using MODFLOW6 and FloPy. The sustainable yield was estimated through a constrained optimization approach, by iteratively running a transient model with different constant pumping rates. This analysis was conducted under a range of scenarios, including contrasting recharge rates, varying degrees of confinement, and multiple planning horizons. Additionally, the effect of transient recharge rates was investigated to understand their relevance on the transient response of the system and the impact on estimated sustainable yields. The modelled response times of this type of systems appear to be highly relevant for planning purposes given the typical human timeframes used for management and policy implementations. Our results reveal that sustainable yield is not a single, fixed value but a dynamic variable dependent on the chosen planning horizon. This analysis illustrates that what might be considered a sustainable withdrawal rate over a 25-year horizon could lead to unacceptable or undesirable impacts over a 50-year period, bringing an important question to the debate: which planning horizon to use? We conclude that effective management of confined aquifers requires a paradigm shift away from steady-state thinking: what is considered sustainable fundamentally depends on when we decide to evaluate it. This demands an adaptive, time-dependent approach where sustainability is analysed within a context-specific planning horizon, acknowledging that our decisions today have consequences that might unfold over decades or even centuries. This introduces broader issues of intergenerational equity, emphasizing that sustainability cannot be determined solely by physical indicators and it must also address long-term governance and ethical considerations.
(27/10/2025)
Bordeaux INP, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, CEREGE, IRD, INRA, AMU, CdF (institution), INSU - CNRS, CNRS
Population dynamics of the potentially invasive Asian date mussel, Arcuatula senhousia, in Arcachon Bay, France
Originated from Asia, Arcuatula senhousia has spread globally and is often reported as an invasive species that alters benthic communities and ecosystem functioning. However, very few studies have focused on the population dynamics of this ecosystem-engineering mytilid, partly due to the difficulty in monitoring cohorts of this short-lived, fast-growing species. Through a one-year monthly monitoring of mussel in two distinct locations in Arcachon Bay, France, we observed higher growth performance and P/B ratio at the station closer to the main river mouth, confirming the species preference for brackish, estuarine conditions. Post-recruitment mortality was particularly high, exceeding typical bivalve mortality rates, likely due to the vulnerability of this small species at the sediment surface. Trematode parasites, absent in our samples, were not implicated in mortality. In both locations, the reproductive phenology was similar, with a prolonged spawning season centred in the warmer months. As of 2024, A. senhousia remains a colonizing introduced species in Arcachon Bay with relatively low densities. However, vigilance is necessary, as its population dynamics resemble those observed in the few areas where these data are available and where this species has become invasive.
(Estuarine, Coastal and Shelf Science. vol. 324, n° 0272-7714, pp. 109448, 15/10/2025)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LERAR, COAST, IFREMER, PatriNat, MNHN, IRD, CNRS, OFB - DSUED, OFB
Aquatic metabolism influences temporal variations of water carbon and atmospheric carbon dioxide fluxes in a temperate salt marsh
Salt marshes are blue carbon (C) ecosystems characterized by intense atmospheric CO2 uptake and C sequestration but also by organic and inorganic C exports through the tide. However, uncertainties about the main biotic factors controlling these vertical and horizontal C fluxes imply studying terrestrial and aquatic metabolisms simultaneously at small timescales (diurnal and tidal) to distinguish their contributions to net ecosystem CO2 exchange (NEE). In a temperate salt marsh, four sampling 24 h cycles were performed to measure all water C biogeochemical parameters (including CO2 partial pressures, pCO2), nutrients, and aquatic metabolism simultaneously to NEE from high tide during marsh immersion (imported coastal waters influenced by the continental shelf) to low tide during marsh emersion (exported channel waters influenced by the marsh drainage). At high tide, water CO2 oversaturation (water pCO2 > air pCO2) due to marsh aquatic heterotrophy and CO2-concentrated water inputs from the coastal end-member induced water–air CO2 emissions during marsh immersion. At low tide, water pCO2 in the channel were also mainly controlled by the marsh aquatic metabolism, inducing a water CO2 oversaturation in winter due to dominant heterotrophy and a water CO2 undersaturation in spring and summer due to dominant autotrophy. In winter, the greatest increases in dissolved inorganic carbon (DIC; from 2354 to 3963 µmol kg−1), total alkalinity (TA; from 2508 to 4016 µmol kg−1) and dissolved inorganic nitrogen (DIN; from 27.7 to 68.4 µM) were measured simultaneously during low tide at night, probably due to intense aerobic/anaerobic microbial respiration of organic matter in channel waters and/or sediments resulting in the greatest water pCO2 increase (from 533 to 1461 ppmv). On the contrary, in spring and summer, large water pCO2 decreases (down to 83 ppmv) and dissolved organic carbon (DOC) increases (up to 1040 µM) from high to low tide could be related to intense autochthonous and allochthonous marsh primary production, including benthic microalgae, phytoplankton and macroalgae. This study suggests that the horizontal exchanges of coastal waters with the salt marsh significantly modify water C dynamics and associated water CO2 sink/source state in the channel due to an intense marsh metabolism (production and respiration). At the daily scale, plant and phytoplankton metabolism rates played a major and a minor role, respectively, in the marsh CO2 sink measured by atmospheric eddy covariance at the ecosystem scale (NEE), even during immersion where emerged plants located on the highest marsh levels can maintain a low CO2 uptake, despite aquatic heterotrophy and associated water–air CO2 emissions.
(Biogeosciences. vol. 22, n° 1726-4170, pp. 5387 - 5411, 08/10/2025)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LERMPL, COAST, IFREMER, LERPC, COAST, IFREMER, DYNECO, IFREMER, UMR MARBEC, IRD, IFREMER, CNRS, UM, BRGM, ISTO, BRGM, INSU - CNRS, UO, CNRS, UMR ISPA, Bordeaux Sciences Agro, INRAE, BOREA, MNHN, IRD, SU, CNRS, UA
Tipping points in ocean and atmosphere circulations
Abstract. Continued anthropogenic pressures on the Earth system hold the potential to disrupt established circulation patterns in the ocean and atmosphere. In this narrative review, we investigate tipping points in these systems by assessing scientific evidence for feedbacks that may drive self-sustained change beyond critical forcing thresholds, drawing on insights from expert elicitation. The literature provides multiple strands of evidence for oceanic tipping points in the Atlantic Meridional Overturning Circulation (AMOC), the North Atlantic subpolar gyre (SPG), and the Antarctic Overturning Circulation, which may collapse under warmer and “fresher” (i.e. less salty) conditions. A slowdown or collapse of these oceanic circulations would have far-reaching consequences for the rest of the climate system and could lead to strong impacts on human societies and the biosphere. Among the atmospheric circulation systems considered, a few lines of evidence suggest the West African monsoon (WAM) as a tipping system. Its abrupt changes in the past have led to vastly different vegetation states of the Sahara (e.g. “green Sahara” states). Despite multiple potential sources of destabilization, evidence about tipping of the monsoon systems over South America and Asia is limited. Although theoretically possible, there is currently little indication for tipping points in tropical clouds or mid-latitude atmospheric circulations. Similarly, tipping towards a more extreme or persistent state of the El Niño–Southern Oscillation (ENSO) is currently not fully supported by models and observations. While the tipping thresholds for many of these systems are uncertain, tipping could have severe socio-environmental consequences. Stabilizing Earth's climate (along with minimizing other environmental pressures, such as aerosol pollution and ecosystem degradation) is critical for reducing the likelihood of reaching tipping points in the ocean–atmosphere system.
(Earth System Dynamics. vol. 16, n° 2190-4979, pp. 1611-1653, 08/10/2025)
PIK, NOC, CAOS, IISc Bangalore, BCCR, BIO / UiB, UiB, USP, IMAU, KNMI, UNSW, LOCEAN-VARCLIM, LOCEAN, MNHN, IRD, INSU - CNRS, SU, CNRS, IPSL (FR_636), ENS-PSL, UVSQ, CEA, INSU - CNRS, X, CNES, SU, CNRS, UPCité, MOHC, IIASA, LDEO, UQAM, NOCS, LOCEAN-PROTEO, LOCEAN, MNHN, IRD, INSU - CNRS, SU, CNRS, IPSL (FR_636), ENS-PSL, UVSQ, CEA, INSU - CNRS, X, CNES, SU, CNRS, UPCité, CCRC, UNSW, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IISc
When invasion is faster than science: the long story of the flatworm who travelled across oceans
Both scientific and policy recommendations on marine non-indigenous species agree on the importance of a rapid detection and identification of species, for a rapid action. But sometimes, detection can just be the beginning of a long investigation, longer than the invasion of the species. In 2020, oyster farmers of the Arcachon Bay (France) noted the presence of a polyclad in cultivated oysters (Magallana gigas). Rapidly, special attention was paid to it because of its potential predatory behavior on bivalves. Because of its absence from public barcode databases until 2023 and from available identification keys, it was described as a new species (Idiostylochus tortuosus) while keeping in mind the high probability to be an introduced non-indigenous species. After several months of investigation, mainly based on molecular markers, the presence of this polyclad in Pacific areas (Australia and Japan)supported this status and finally allowed its identification as Postenterogonia orbicularis described from New-Zealand. Meanwhile, the species took the opportunity to proliferate both in terms of spatial expansion and population densities. This poster aimed to detail the investigation about this traveler polyclad and first results of population dynamic in the Arcachon Bay, acquired during two successive projects, RAPSODI (IFREMER) and VISQUEUX (FEAMPA-OFB).
(07/10/2025)
PatriNat, MNHN, IRD, CNRS, OFB - DSUED, OFB, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IRSTEA, LERAR, COAST, IFREMER, LERPC, COAST, IFREMER, CAPENA
One decade of monitoring the consequences of different forest management alternatives on ecosystem functioning in young plantations
The global demand for wood biomass is increasing, therefore it is necessary to develop forest management alternatives that can, simultaneously, produce large amounts of biomass and maintain ecosystem functions and services in a sustainable way. However, assessing the consequences of silviculture is challenging, as forest ecosystems function slowly over long periods of time. Therefore, in this study, an experimental platform was set up to monitor the long-term effects of several forest management alternatives (FMA) on ecosystem functioning in a pine forest in a temperate region characterised by oligotrophic conditions. In practice, we monitored three contrasting FMA over a decade: (i) wood biomass production (WBP), designed using an approach of very intense forestry (high stand density; seed lot of pines selected to growth fast), (ii) combined objective management (COM; low stand density), aimed at improving pine growth by alleviating any competition by spontaneous vegetation, and (iii) nutrient management (NuM; medium stand density), designed to improve tree nutrition using N-fixers in the stand furrows. Overall, although FMA showed contrasting stand growth and structures, they had modest effects on forest biogeochemistry over a decade of monitoring: FMA showed similar trends regarding atmospheric deposition, soil solution chemistry and water table-ditch chemistry. The main difference observed was a more important role of dissolved organic matter in NuM biogeochemical functioning. Conversely to their effects on biogeochemistry, the FMA appeared to influence the biophysical properties of stands. The WBP management (with high stand density) was shown to be shadier, cooler and wetter than the other FMA. This trend was fairly clear during the summer periods although differences were observed all year-long. An important result regarding biophysical effects was that, in addition to being observed in the topsoil layers, they were also evident in deeper soil layers and in the water table. All in all, our results indicated that contrasting FMA have tended to influence the ecosystem functioning, in particular its biophysical component, but showed no early sign of unsustainable biogeochemical functioning. Nonetheless, this latter result should be confirmed in the long-term through further monitoring.
(06/10/2025)
UMR ISPA, Bordeaux Sciences Agro, INRAE, UEFP, INRAE, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS