Dynamics of coarse particulate matter in the turbidity maximum zone of the Gironde Estuary
There is a lack of studies devoted to coarse particulate matter (CPM) in estuaries, although this fraction can disturb activities that filter large volumes of water, such as industrial or fishery activities. In the macrotidal and highly-turbid Gironde Estuary, a monthly sampling of CPM was performed in 2011 and 2013 at two stations in the Turbidity Maximum Zone (TMZ) to understand its seasonal, tidal and hydrological dynamics. Regardless of the season and station, low quantities of CPM (few g m3) were observed in comparison with suspended particulate matter (several 103 g m3). The highest concentrations were consistently recorded in bottom waters and at the upstream station. Whereas there is no clear link between the CPM present in the column water and spring or neap tides, an increase in the CPM size has been identified at the two stations after a flood event, fact potentially critical regarding filtering functioning of estuarine activities.
(Comptes Rendus. Géoscience. vol. 346, n° 1631-0713, pp. 28-36, 22/04/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, EDF [E.D.F.], UR EABX, IRSTEA
Fluid Seepage in Relation to Seabed Deformation on the Central Nile Deep-Sea Fan, Part 2: Evidence from Multibeam and Sidescan Imagery,
On the central Nile deep-sea fan, stratified sediments overlying mass-transport deposits (MTDs) are deformed into slope-parallel seabed undulations associated with fluid seepage. The western part of this system, in water depths of 1,950-2,250 m, is examined using multi-frequency data from hull-mounted and deep-towed swath/profiling systems. Sub-bottom profiles show sub-vertical fluid pipes that terminate both at and below seabed, and gas signatures along fault planes bounding the undulations. Fluid seepage is recorded by high- to intermediate-backscatter patches (HBPs, IBPs) that differ in appearance on multibeam imagery (30 kHz, ≤3 m penetration) and sidescan swaths (170/190 kHz, <0.1 m penetration). Comparison of the two suggests a distinction of (a) buried carbonates (0.1-3 m), (b) broad near-seabed (<0.1 m) carbonate pavements elongate along the undulations, (c) sub-circular areas of seabed seepage up to 300 m across. Four of the latter have narrower gas flares at their edges rising 400-800 m above seabed. These results are consistent with an evolving system of narrow fluid conduits that support the growth and burial of carbonate pavements, shifting over millennial timescales along linear zones parallel to fault planes rooted in MTDs. Sediment deformation above MTDs is inferred to provide pathways for fluid escape, but migration of gas-rich fluids from depth is likely to have facilitated slope destabilisation
(Advances in Natural and Technological Hazards Research. vol. 37, pp. 141-150, 22/04/2026)
OGS, GEOAZUR 7329, INSU - CNRS, UniCA, CNRS, IRD [Occitanie], UniCA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IFREMER
Identification of Hg-bearing phases and fluxes in the sedimentary record of laguna del Plata, central Argentina
(Revista Mexicana de Ciencias Geológicas. vol. 31, n° 1026-8774, pp. 104-115, 22/04/2026)
UB, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, SPE, CNRS, Bordeaux INP, UBM
Quantification of MTE in surface sediments of Morbihan Coast (South Brittany, France): A preliminary approach for determination of sources and dynamics
The Morbihan Coast (South Brittany, France) has an intense coastal activity: farming, industry, urban habitation runoff , yachting and transportation. In the past centuries, tin mining industry was also developed. These different factors may introduce metal trace elements (MTE) into the marine environment at toxic concentration levels. This pollution can particularly affect the oyster production, widely developed in the area. Monitoring MTE in surface sediments at high spatial resolution has been programmed to assess pollutants and their sources in two of the major Morbihan coastal systems concerned with oyster farming, and where available information on MTE impact and sediment quality is limited: the Bay of Quiberon, partly protected from the open ocean by the Quiberon Peninsula and several islands, mostly sandy (coarse to fine, with a significant shelly fraction), with water depths shallower that 25 m, and the Gulf of Morbihan, a shallow depth (less than 5 m, apart from the two paleoriver beds), semi-enclosed, estuarine system with very coarse sand to fine mud, mostly distributed by a strong tidal current system. Fifty two surface sediment samples were collected in April 2013 to characterize the MTE spatial distribution through the salinity and pollution gradients, from the small local rivers and harbor areas to the open marine environments. Analyses cover sedimentological and biogeochemical properties (particulate organic carbon using a LECO-CS-230; MTE using ICP-MS or DMA for Hg). Statistical analyses help to discriminate within the spatial variability the natural (e.g. grain-size effect) and anthropogenic factors. MTE concentrations were also compared to local geochemical background as measured at the bottom of three sediment cores collected in representative sites, for calculating the enrichment index of each MTE and evaluating the degree of sediment contamination. The initial interpretation of the results would indicate a clear distinction between the geochemical gradients linked to natural processes: sediment sources and size fractionation (for example, the relationship between Sr and car-bonate concentration in the sand fraction), and gradients linked to polluting factors, in particular in the harbors and protected arias, probably associated with boat maintenance (with Cu, Zn and Sn concentrations exceeding 100 ppm, up to 300 ppm in isolated places). More detailed statistical analyses and implications will be presented at the conference.
(. vol. 16, 22/04/2026)
LGO, UBS, IFREMER, UBO EPE, CNRS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Evidence for a three-phase sequence during Heinrich Stadial 4 using a multiproxy approach based on Greenland ice core records
Glacial climate was characterised by two types of abrupt events. Greenland ice cores record Dansgaard-Oeschger events, marked by abrupt warming in-between cold, stadial phases. Six of these stadials appear related to major Heinrich events (HEs), identified from ice-rafted debris (IRD) and large excursions in carbon-and oxygen-stable isotopic ratios in North Atlantic deep sea sediments, documenting major ice sheet collapse events. This finding has led to the paradigm that glacial cold events are induced by the response of the Atlantic Meridional Overturning Circulation to such massive freshwater inputs, supported by sensitivity studies conducted with climate models of various complexities. These models also simulate synchronous Green-land temperature and lower-latitude hydrological changes. To investigate the sequence of events between climate changes at low latitudes and in Greenland, we provide here the first 17 O-excess record from a Greenland ice core during Dansgaard-Oeschger events 7 to 13, encompassing H4 and H5. Combined with other ice core proxy records, our new 17 O-excess data set demonstrates that stadials are generally characterised by low 17 O-excess levels compared to interstadials. This can be interpreted as synchronous change of high-latitude temperature and lower-latitude hydrological cycle (relative humidity at the oceanic source of evaporation or change in the water mass trajectory/recharge) and/or an influence of local temperature on 17 O-excess through kinetic effect at snow formation. As an exception from this general pattern, stadial 9 consists of three phases, characterised first by Greenland cooling during 550 ± 60 years (as shown by markers of Greenland temperature δ 18 O and δ 15 N), followed by a specific lower-latitude fingerprint as identified from several proxy records (abrupt decrease in 17 O-excess, increase in CO 2 and methane mixing ratio, heavier δD-CH 4 and δ 18 O atm), lasting 740 ± 60 years, itself ending approximately 390 ± 50 years prior to abrupt Greenland warming. We hypothesise that this lower-latitude signal may be the fingerprint of Heinrich event 4 in Greenland ice cores. The proposed decoupling between stable cold Greenland temperature and low-latitude climate variability identified for sta-dial 9 provides new targets for benchmarking climate model simulations and testing mechanisms associated with millen-nial variability.
(Climate of the Past. vol. 10, n° 1814-9324, pp. 2115-2133, 22/04/2026)
LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, NBI, UCPH, GLACCIOS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, PALEOCEAN, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA
Influence des hydrophytes envahissants sur la biogéochimie des lacs peu profonds
Influence des hydrophytes envahissants sur la biogéochimie des lacs peu profonds (influence sur les dynamiques de l'oxygène et du carbone dissous, dont le méthane).
(pp. 14, 22/04/2026)
UR EABX, IRSTEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Amélioration de l’élimination des micropolluants des eaux usées grâce aux procédés tertiaires intensifs et extensifs
Amélioration de l’élimination des micropolluants des eaux usées grâce aux procédés tertiaires intensifs et extensifs compléments sur http://armistiq.irstea.fr/journee-de-restitution
(pp. 2, 22/04/2026)
UR MALY, IRSTEA, IRSTEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Etude intégrée de l’effet des apports amont et locaux sur le fonctionnement de la Garonne estuarienne (ETIAGE) : Axe 5 Synthèses des pressions et des impacts caractérisant les eaux de la Garonne estuarienne. Recommandations de gestion
Le programme ETIAGE a été mis en place avec pour objectif de répondre aux questions suivantes : que représentent les apports des effluents de la Communauté Urbaine de Bordeaux (CUB) par rapport à ceux venant de l’amont en termes de charge organique et de micro-polluants ? Quels rôles sur le devenir des effluents jouent la présence du bouchon vaseux et la stagnation résiduelle des eaux (déplacement net entre mouvement de flot et de jusant) au niveau de l’estuaire fluvial amont en période d’étiage estival ? Réciproquement, à quels moments et jusqu’où s’étend l’impact de ces effluents sur la qualité des eaux de la Garonne estuarienne ? Quelles incidences des effluents sur le comportement des populations biologiques en place ou migratoires dans la Garonne estuarienne ? Quelle tendance évolutive va connaître l’oxygénation des eaux ? Quel sera l’impact sur le comportement des micro-polluants et des populations biologiques ? Quelles recommandations de gestion pourraient être préconisées à partir de la synthèse des pressions exercées sur les eaux de la Garonne estuarienne ? Une présentation très synthétique des résultats, obtenus sur les quatre années du programme, est donnée : axe Caractérisation et rôle respectif des apports organiques amont et locaux sur l’oxygénation des eaux de la Garonne estuarienne ; axe 2 Caractérisation et flux des contaminants organiques (classiques et émergents) dans les eaux de la Garonne estuarienne ; axe 3 Apports métalliques de la CUB à la Gironde ; axe 4 actions 1 et 3 Inventaire et caractérisation saisonnière de la macrofaune présente (poissons et crustacés) dans la masse d’eau sous influence directe des apports de l’agglomération bordelaise; étude des effets des périodes hypoxiques sur les fonctionnements biologiques ; axe 4 action 2 : Approche de l’impact des conditions physico-chimiques affectant la masse d’eau estuarienne garonnaise sur les cortèges biologiques ; axe 4 action 4 Evaluation des niveaux de contamination et effets toxicologiques sur les composantes biologiques exposées dans la masse d’eau estuarienne garonnaise.
(pp. 21, 22/04/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, CNRS, UB, IRSTEA, UR EABX, IRSTEA
Importance, but not intensity of plant interactions relates to species diversity under the interplay of stress and disturbance
The lack of clarity on how the intensity and importance of plant interactions change under the co-occurrence of stress and disturbance strongly impedes assessing the relative importance of plant interactions for species diversity. We addressed this issue in subalpine grasslands of the French Pyrenees. A natural soil moisture gradient further experimentally stretched at both ends was used and a mowing disturbance treatment was applied at each position along the soil moisture gradient. Changes in intensity and importance of plant interactions were assessed by a neighbour removal experiment using four target ecotypes. A structural equation modelling approach was used to assess the relative impact of stress, disturbance, the intensity and importance of plant interactions on diversity at both the neighbourhood and community scales. Without mowing, changes in intensity and importance of plant interactions only diverged in the dry part of the soil moisture gradient. The intensity of plant interactions linearly shifted from competition to facilitation with increasing stress, while the importance followed a hump-shaped relationship. Species diversity components were tightly related to the importance of plant interactions only, both the neighbourhood and community scales. Mowing disturbance strongly reduced the importance of facilitation along the soil moisture gradient, and suppressed the relationship between the importance of plant interactions and diversity components. Together, our results highlight that 1) the importance is the best predictor of variations in species diversity in this subalpine herbaceous system, and 2) that fine-scale processes such as plant interactions can affect the entire plant communities. Finally, our results suggest that high level of constraints due to co-occurring stress and disturbance can inhibit the effects of plant interactions on species diversity, highlighting their potential role in regulating diversity and the maintenance/extinction of plant communities.
(Oikos. vol. 123, n° 0030-1299, pp. 777–785, 22/04/2026)
UB, BioGeCo, INRA, UB, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Impact du métolachlore sur la physiologie et le comportement de la diatomée dulçaquicole Gomphonema gracile
Les micro-algues jouent un rôle fondamental dans les écosystèmes aquatiques : elles sont à la base des réseaux trophiques et ce en raison de leur statut de producteurs primaires. Au sein des milieux aquatiques, elles peuvent ainsi être directement impactées par des molécules de type herbicide provenant des écosystèmes terrestres et retrouvées dans le milieu par des phénomènes de ruissellement, drainage, infiltration et lessivage des sols. Cependant, les descripteurs actuels (croissance, fluorescence chlorophyllienne) s’avèrent parfois peu sensibles pour détecter les impacts toxiques de molécules dont la cible n’est pas le photosystème. Dans ce contexte, cette étude a pour but de quantifier l’impact de l’herbicide métolachlore (inhibiteur des élongases) sur une espèce de diatomée dulçaquicole Gomphonema gracile Ehrenberg, mise en culture et isolée du milieu d’étude, la Leyre (principal tributaire du bassin d’Arcachon). Cet herbicide est le contaminant majoritaire du bassin versant (en termes de fréquence de quantification et de concentration). Sa toxicité est évaluée sur des paramètres physiologiques (croissance, photosynthèse, concentration en ATP) et comportementaux (mobilité). Alors que les descripteurs classiques (par exemple l’activité photosynthétique) ne permettent pas de mettre en évidence d’impact toxique du métolachlore, et ce quelle que soit la concentration testée, les descripteurs de mobilité (pourcentage de cellules mobiles, vitesse de déplacement) démontrent des impacts toxiques, pour des concentrations environnementales. Nos résultats soulignent l’importance de l’utilisation de descripteurs d’effet diversifiés, et démontrent le potentiel prometteur d’indicateurs comportementaux pour la mise en évidence de contaminations toxiques.
(pp. 22, 22/04/2026)
UR EABX, IRSTEA, IFREMER, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS