Understanding the relationship between foraminiferal Mg/Ca and clumped isotope thermometers
Reconstructions of past sea surface temperatures (SSTs) are essential for understanding long-term climate variability, yet different proxy methods can yield divergent results. In this study, we compare Mg/Ca-derived SSTs from Globigerinoides ruber sensu stricto and Trilobatus sacculifer with clumped isotope (Δ 47 ) SSTs measured on G. ruber s.s. from the same core, MD96-2048 (Indian Ocean), covering the last 1.25 million years (Ma). Using the same species and samples allows minimizing ecological and environmental biases. We find that Δ 47 -derived SSTs are systematically colder than Mg/Ca-SSTs prior to 0.4 Ma, while both proxies agree well after this point. This offset is not explained by diagenetic alteration (as assessed via SEM), nor by corrections for seawater salinity, pH, or Mg/Ca composition. The Mg/Ca-SSTs from T. sacculifer are more consistent with Δ 47 -SSTs in the older interval, but do not fully resolve the discrepancy. We found that the apparent Δ 47 -based cooling before 0.4 Ma is not supported by seawater δ 18 O estimates or other climate indicators. Our results suggest that Δ 47 -derived SSTs may be affected by an unknown bias in older intervals, although a combination of multiple factors explored in this study could also contribute to the observed offset.
(Geochimica et Cosmochimica Acta. vol. 407, n° 0016-7037, pp. 253 - 264, 01/10/2025)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, VUB, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, GLACCIOS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, PALEOCEAN, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA
Quantitative structural geology in the deep ocean using photogrammetry: Implications for the polyphased tectonic evolution of the Buteur Ridge, French Guiana
The Buteur Ridge is a 7 km-long and 6 km-wide relief on the eastern rifted margin of the Demerara Plateau, offshore French Guiana. This margin was formed during the Lower Cretaceous. In early 2023, the oceanographic cruise DIADEM used a manned deep submersible (Nautile) to sample and directly observe the eastern flank of this 3750 m-deep ridge. This study presents a new underwater photogrammetric method developed from the Nautile video records. This method incorporates both camera and submarine movements to produce photogrammetric 3D models of the seafloor below decimetre scale. The presented underwater photogrammetric method can be used for both past and future video records, as long as both underwater device and camera movements are recorded. The data obtained from the 3D reconstructions allow to reconstruct detailed stratigraphic and structural framework of the Buteur Ridge. The eastern flank of the Buteur Ridge is entirely composed of sedimentary layers. Structural analysis at bed scale suggests prograding structures likely associated with a N-S-directed paleocurrent. At ridge scale, structural analysis combined with seismic observations suggests that the Buteur Ridge is the result of a polyphased tectonic evolution. We highlight that Cretaceous tilted blocks, bounded by east-dipping faults, are overlapped by a post-rift unit. The syn-rift units are in contact with the east-dipping post-rift unit by a post-rift unconformity. Subsequent tilt and fault reactivation offset both the post-rift unconformity and the post-rift unit, resulting in the present relief of the Buteur Ridge.
(Marine Geology. vol. 488, n° 0025-3227, pp. 107609 (19p.), 01/10/2025)
ISTerre, IRD, INSU - CNRS, USMB [Université de Savoie] [Université de Chambéry], CNRS, Fédération OSUG, UGA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, GEO-OCEAN, UBS, IFREMER, INSU - CNRS, UBO EPE, CNRS, CEFREM, UPVD, INSU - CNRS, CNRS
From Carbon to Societal Footprint: Geoscience Research in the Face of the Socio-Environmental Emergency
(29/09/2025)
GR, UR, INSU - CNRS, CNRS, IMBE, AU, AMU, CNRS, IGE, IRD, INSU - CNRS, CNRS, INRAE, Fédération OSUG, UGA, Grenoble INP, UGA, IMPMC, MNHN, SU, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LCE, CNRS, UFC, UBFC, GET, IRD, INSU - CNRS, CNES, CNRS, EPE UT, Comue de Toulouse, HSM, IRD, INSU - CNRS, CNRS, UM, CEREGE, IRD, AMU, CdF (institution), INSU - CNRS, CNRS, INRAE
Multi‐decadal gravel beach dynamics in the United Kingdom and Ireland: Insights from satellite‐derived shorelines
Gravel beach systems provide vital protection from coastal flooding and erosion. They are highly dynamic and exhibit complex responses to hydrodynamic forcing over a range of temporal (hourly centennial) and spatial scales (m to km). Yet gravel beach evolution, particularly at interannual to decadal scales, across the spectrum of coastal settings, remains poorly understood. We use four decades of Satellite-Derived Shoreline (SDS) data to explore the morphodynamic behaviour of 45 selected gravel beach systems around the United Kingdom and Ireland. We apply a site-specific SDS extraction methodology and derive shoreline trends along 1554 shore-normal transects. Our findings indicate significant variability in decadal trends between sites ranging from 0.60 m/year retreat to 2.24 m/year progradation, with 36% of sites showing significant long-term trends over the study period. Nesses and spits were by far the most dynamic systems exhibiting the largest changes at transect level (from 4.73 m/year retreat to 10.5 m/year progradation), and the most significant changes in planform shape, while most constrained and unconstrained sites remained stable. We classify the observed behaviours, providing a first inventory of morphodynamic behaviours across different gravel beach systems in the United Kingdom and Ireland. We find that leading regional winter-averaged atmospheric indices provide some insight into planform behaviour over the entire domain, with 16 sites (35.6%) showing at least moderate (R ≥ 0.4) statistically significant correlations (p ≤ 0.05). Our results provide a deeper understanding of the long-term behaviour of gravel beach systems that can inform more effective coastal management strategies.
(Earth Surface Processes and Landforms. vol. 50, n° 0197-9337, pp. e70160, 17/09/2025)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Rapport de campagne DIADEM
En Janvier-Février 2023, la campagne DIADEM (Deep Investigations At DEMerara, ou DIve At DEMerara) s’est déroulée à bord du Navire Océanographique Pourquoi Pas ?, au Nord-Est du plateau sous-marin de Demerara, au large de la Guyane française et du Suriname. Cette campagne océanographique a utilisé une panoplie d’outils de mesures, de prélèvement et d’observation en fond de mer : le Nautile, sous-marin d’observation et de prélèvements, l’AUV (Autonomous Underwater Vehicle) IdeFx opérant des mesures géophysiques près du fond (cartographie bathymétrique, sondeur de sédiment, courants et paramètres physiques des eaux de fond), un mouillage pour mesurer les variations temporelles des courants et des paramètres physiques des eaux de fond, des carottiers pour prélever des sédiments meubles (Calypso pour une carotte d’une trentaine de mètres de long, Fantacore pour des carottes métriques préservant l’interface entre l’eau de fond et le sédiment), et une drague pour prélever des roches indurées.Cette campagne était multidisciplinaire et multisites. Les deux principaux objectifs étaient de:-Comprendre l’interaction entre les courants de fond, la morphologie du fond de la mer, et la sédimentation récente. La partie du plateau de Demerara étudiée pour cette thématique est balayée par la North Atlantic Deep Water (NADW), qui s’y écoule vers le Sud-Est. Cet écoulement est marqué dans la morphologie par des dépressions allongées (nommées queues de comètes), initiées sur des reliefs (nommés têtes de comètes). Le champ de comètes « Tangara » a été étudié en détail grâce à 6 plongées AUV, 4 plongées Nautile, (incluant des carottages d’interface au moyen de push-cores) et un mouillage. Sept autres sites ont été carottés autour de Tangara, afin d’obtenir une archive sédimentaire la plus complète possible dans les zones contouritiques présentant les taux de sédimentation maxima.Les observations faites pendant la campagne montrent que les têtes de comètes sont constituées de carbonates lités, souvent fortement basculés, et ont confirmé le rôle des courants de fond dans la sédimentation et morphologie sous-marine du secteur.-Cartographier et échantillonner les roches pre- et syn-rift affleurant sur la bordure du plateau. Cela concernait deux horsts ou blocs basculés (Plateau Bastille et Ride Buteur) sur la bordure Est du plateau (marge divergente), et différents sites (Ride des 60°, Canyon Poubelle) sur la bordure Nord du plateau (marge transformante), avec un socle formé de coulées basaltiques héritées du rifting Jurassique, recouvert par des séries sédimentaires associées au rift Crétacé. Au total, 6 plongées Nautile et 6 dragues ont permis d’observer et/ou d’échantillonner autant de coupes, et ont confirmé la nature presque exclusivement basaltique du socle du plateau.-Enfin, deux plongées Nautile ont été dédiées à des objets pouvant être associés à la sortie en fond de mer de fluides profonds. Une plongée a eu lieu sur une structure en forme de dôme, initialement supposée être un volcan de boue, mais qui s’est révélée être composée d’un empilement de carbonates lités. Une autre plongée a eu lieu dans la cicatrice sommitale des glissements gravitaires affectant le Nord Est du plateau de Demerara.-L’ensemble des plongées a observé une densité d’organismes importante en fond de mer. Des champs de nodules polymétalliques ont également été observés, associés aux affleurements de basaltes.
(16/09/2025)
ISTerre, IRD, INSU - CNRS, USMB [Université de Savoie] [Université de Chambéry], CNRS, Fédération OSUG, UGA, CEFREM, UPVD, INSU - CNRS, CNRS, UGA, GEO-OCEAN, UBS, IFREMER, INSU - CNRS, UBO EPE, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, HNHP, MNHN, UPVD, CNRS, LOCEAN-CYBIOM, LOCEAN, MNHN, IRD, INSU - CNRS, SU, CNRS, IPSL (FR_636), ENS-PSL, UVSQ, CEA, INSU - CNRS, X, CNES, SU, CNRS, UPCité, UG, INSU - CNRS, CNRS, UA, UM
Orbital-scale competition of biogenic carbonate and opal production and its implication on carbon cycle at Del Caño Rise in the Indian sector of the Southern Ocean
Geochemical properties measured in core MD19-3575CQ, collected from the Del Ca˜no Rise within the Subantarctic Zone in the Indian sector of the Southern Ocean, provide evidence of orbital-scale changes over eccentricity, obliquity, and precession cycles in phytoplankton productivity and its influence on the organic matter burial over the last 235 kyr. CaCO3 and biogenic opal contents varied oppositely with high CaCO3 and low biogenic opal contents during the interglacial periods and vice versa during the glacial periods. During the glacial periods, the biogenic opal production by diatoms increased as a result of more silica supply when the Subantarctic Front shifted northward across the Del Ca˜no Rise. In addition, Fe-bearing dust and remobilized sediments likely enhanced diatom productivity. In contrast, biogenic carbonate production by coccolithophores and foraminifera was reduced during the glacial periods because of cold ocean temperature and competition for nutrients between coccolithophores and diatoms. More organic carbon was buried at the core site during the glacial periods than during the interglacial periods, probably in relation to a greater export efficiency by diatoms relative to coccolithophores as well as a better preservation of the organic matter when the Circumpolar Deep Water was less ventilated during the glacial periods.
(Palaeogeography, Palaeoclimatology, Palaeoecology. vol. 679, n° 0031-0182, pp. 113290, 15/09/2025)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Lateglacial and Holocene mountain glacier fluctuations near Cape Farewell South Greenland inferred from 10 Be moraine dating
ABSTRACT We report 43 new 10 Be exposure ages and six 26 Al/ 10 Be measurements from replicates from a small piedmont mountain glacier located at Cape Farewell (south Greenland) and temperature anomalies estimated from equilibrium‐line altitude (ELA) changes derived from 3D glacier reconstruction carried out using the ‘GlaRe’ toolbox. Both ELA‐derived temperature estimations and climate conditions documented from the transient simulation TraCE‐21ka help us to explore the causes of glacier changes during the investigated period. Exposure ages span from the Oldest Dryas to the Late Holocene, revealing that the GrIS retreat in this valley permitted the individualisation or formation of a mountain glacier early in the Lateglacial. Interestingly, four of the six 26 Al/ 10 Be ratios come from samples located on the oldest moraines do not reveal inheritance. The two other ratios suggest inheritance up to 6 ka. The oldest moraine combining a frontal and a lateral remain is dated to 18.4 ± 0.8 ka. Between 18 ka and ~14.7 ka, the glacier experienced a significant retreat interrupted by at least three minor advances or stillstands. We did not find any moraine formed either during the Younger Dryas, or during the Early and the Mid Holocene. The largest Holocene glacier advance occurred ~4.4 ka. Two other younger moraines were formed at ~2.9 ka and probably during the LIA. Temperatures of 3.3°C and 1.7°C colder than today may explain the glacier extent during the Lateglacial and the Holocene, respectively. Complementary dry regional climate conditions estimated from TraCE‐21ka simulations during the Early Holocene may explain why the glacier was smaller than during the Late Holocene.
(Journal of Quaternary Science, n° 0267-8179, 14/09/2025)
CEREGE, IRD, AMU, CdF (institution), INSU - CNRS, CNRS, INRAE, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Bridging the gap: oxygen and nutrient budgets in the Loire estuary using a benthic-pelagic box model
In hypoxic estuaries, sediment feedback is clearly a key factor in nutrient and oxygen cycling, favouring nutrient enrichment and oxygen depletion in the water column. It is crucial to understand these mechanisms to implement effective management strategies for these coastal systems. In this study, a coupled benthic-pelagic box model was developed to assess the impact of sediment and water column processes on nutrient and dissolved oxygen stocks in a hypoxic estuary. The model integrates physical and biogeochemical processes, focusing on the sediment-water column interaction during two contrasting hydrological contexts sampled in 2021: a winter flood and a summer low discharge period. The model reproduces the main processes well, despite some discrepancies with the observed data due to the underlying assumptions, which are discussed. The winter flood caused substantial erosion of upstream sediments, resulting in a strong redox gradient and high sediment-water exchange. The short residence time of the water prevented solutes accumulation, minimising their influence on oxygen and nutrient stocks. In summer, under low flow conditions, benthic recycling to the water column is intensified, resulting in an increase in ammonium concentration of up to 91%, compared to 67% from pelagic processes. In contrast, phosphate release remains modest (around 4%), particularly from the sediments underneath the Turbidity Maximum Zone (TMZ), where benthic exchange is limited by the presence of an oxide-rich sediment layer that acts as a barrier. However, phosphate availability in summer is primarily driven by pelagic desorption from suspended particles, notably in the TMZ. The results clearly highlight a decoupling between nitrogen and phosphorus recycling, which is promoting nitrogen enrichment and potentially favouring harmful algal blooms and hypoxia. The proposed simplified modelling approach is a crucial step in identifying the estuarine processes controlling oxygen and nutrient dynamics and can be easily applied to any estuary.
(Science of the Total Environment. vol. 1000, n° 0048-9697, pp. 180446, 11/09/2025)
LPG, UM, UA, INSU - CNRS, CNRS, Nantes univ - UFR ST, Nantes Univ, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IPREM, UPPA, INC-CNRS, CNRS, CHROME, UNIMES, LERMPL, COAST, IFREMER
Exploring Future Shoreline and Nearshore Evolution Under Sea-Level Rise Projections: Application of the LX-ST Model to Lacanau
This study applies the reduced-complexity model LX-ST to simulate the future evolution of the shoreline and nearshore morphology of Lacanau, a wave-dominated, erosion-prone coastal site in southwest France. By coupling longshore transport with shoreface translation processes, the model evaluates changes under various IPCC sea-level rise scenarios through 2100. Results highlight significant spatial variability in erosion, with pronounced downdrift retreat near coastal defenses. The findings demonstrate the utility of LX-ST for informing long-term coastal adaptation strategies.
(01/09/2025)
BRGM, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
A small increase in temperature could rapidly expand the latitudinal range and pathogenicity of the marine trematode parasite Curtuteria arguinae
The phenology and transmission dynamics of the marine trematode Curtuteria arguinae were investigated, a parasite whose recently elucidated life cycle involves oystercatchers (Haematopus ostralegus), needle snails (Bittium reticulatum), and edible cockles (Cerastoderma edule). To assess the influence of temperature and light on cercarial emergence, infected B. reticulatum were exposed to temperatures ranging from 15 °C to 27 °C under both light and dark conditions. Cercarial emergence peaked under warm and illuminated conditions, showing strong temperature dependence, and, to a lesser extent, light dependence. Emergence occurred significantly at temperatures ≥21 °C, with median emergence rates of 12–47 cercariae.day−1, and the positive influence of light was overruled at higher temperatures. A 22-year dataset from Arcachon Bay (France) was also analyzed to determine the timing of first infections in cockles relative to sea and air temperatures, as well as cockle shell size, across ten cohorts. First infections of cockles were consistently observed in late summer, with a mean sea temperature of 20.8 °C, placing cercarial transmission once a thermal threshold is reached. This thermal dependency explains the parasite's current southern distribution. With climate warming, its range is likely to expand northward along the northeastern Atlantic coast, in areas where all hosts are already present. Expansion may also be supported by the northward extension of B. reticulatum. In areas where the parasite is already established, rising temperatures may enhance cercarial output and infection intensity, increasing pathogenic effects on both intermediate hosts and posing a growing threat to ecosystem functioning and cockle fisheries.
(Estuarine, Coastal and Shelf Science. vol. 326, n° 0272-7714, pp. 109541, 01/09/2025)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, OASU, UB, INSU - CNRS, ULR, CNRS, INRAE, SU, SBR, SU, CNRS, ECOMAP, AD2M, CNRS, SBR, SU, CNRS