Forecasting winter wave height using decadal prediction of atmospheric indices over the Northeast Atlantic
Forecasting wave height variability on a decadal timescale is important from many perspectives, including the anticipation of coastal hazards. We propose a hybrid prediction system for forecasting winter wave height, from the multi-annual to the decadal timescales, using decadal climate predictions and regression models. We focus on the Northeast Atlantic, where the variability of winter wave height is primarily controlled by two large-scale atmospheric indices: the North Atlantic Oscillation (NAO) and the West Europe Pressure Anomaly (WEPA). Leveraging recent advances in prediction skills, decadal climate predictions of the NAO and WEPA are used as predictors of wave height. Hindcasts results over the period 1962-2024 demonstrate high skills for the western European coasts, especially for decadal variability, with NAO (WEPA) dominating predictability at the northernmost (southernmost) latitudes. Moreover, by implementing a multivariate linear regression model, a significant improvement in skill is observed between the two zones of influence of the NAO and the WEPA. The proposed methodology is generic and robust, and could be applied to other ocean regions where multi-annual to decadal variability in wave height is large. This approach also forms the foundation of a climate service that could be developed for coastal managers to better anticipate coastal hazards across relevant timescales.
(Climate services. vol. 44, n° 2405-8807, pp. 100723, 01/12/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Establishing experimental characterization of the thermal conductivity of limestone substrate under different water saturation indices to improve heat transfer knowledge
Geothermal heat exchangers are currently dimensioned using mathematical models that only consider conductive heat transfers where water content is not considered. However, considering water could improve geothermal exchange dimensioning. To understand the effect of water on thermal conductivity, we focus on the unsaturated zone characterized by its capacity to store and transfer heat and, also, strongly affected by variations in water content. Heterogeneous limestones in an unsaturated zone over a depth of 20 m deep were investigated in the laboratory. To measure the thermal conductivity at different water contents, two methods were considered: (1) the direct thermal conductivity method and (2) an indirect estimation through acoustic measurements using an empirical model originally developed for dry conditions. The applicability of this empirical approach beyond its initial domain is therefore explored. Both methods show coherent results in dry conditions (λ dry = 1.5 and 1.3 W. m -1 .K -1 for direct and indirect methods) highlighting the usefulness of the indirect, and easier, method. For saturated or partially saturated materials however, the indirect method presents apparent inconsistencies, while for some samples, of rather massive appearance, only slightly altered and fractured, water content has a relatively low impact on thermal conductivity. This indirect approach, when used with a dry-based empirical model, shows clear limitations in capturing the effect of water in the pores of complex rocks. The direct method, which directly measures the thermal conductivity of a small area at the sample surface, shows an increase in thermal conductivity with water saturation. Finally, we discuss the limits of both methods considering the microstructures of the samples.
(International Journal of Thermal Sciences. vol. 229, n° 1290-0729, pp. 111091, 01/11/2026)
ISTO, BRGM, INSU - CNRS, UO, CNRS, OSUC, INSU - CNRS, CNRS, PSL, UO, CNRS, LOMC, ULH, NU, CNRS, BRGM, LaMé, UO, UT, NEOLAiA, INSA CVL, INSA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Legacy PCB and hydrocarbon reservoirs in estuarine sediments: from historical contamination to hidden mass hotspots
Infrastructure-induced sediment deposits are common features in engineered river systems, yet their role as longterm reservoirs of persistent organic pollutants remains poorly quantified. The upper Seine Estuary (France), historically affected by intense industrial contamination and extensive river engineering, provides a relevant example of this issue. Here, we combined near-infrared hyperspectral imaging, 3D stratigraphic modelling and sediment-thickness-based extrapolation to quantify depth-integrated and spatially explicit stocks of polychlorinated biphenyls (PCBs) and total hydrocarbons (THC) across three infrastructure-induced sediment deposits. Sediment records revealed high historical contamination, with PCBs reaching 2.59 mg kg -1 during the 1970s, followed by a marked decline, while THC exhibited a similar temporal trend. Total stocks were estimated at 128 ± 67.9 kg for PCBs and 55.5 .10 3 ± 20.8 .10 3 kg for THC over only 0.1 km² of sediment deposits. Accordingly, surface-normalized PCB storage averaged 1310 mg m -2 , several orders of magnitude higher than values reported for other estuarine environments worldwide (0.01 -4.4 mg m -2 ). These exceptionally high stocks result from sustained historical contaminant inputs from nearby industrial sources and enhanced sediment accumulation promoted by river engineering works. Importantly, the uppermost 5 cm, commonly considered in stock assessments, contained only 0.4 % of the total PCB stock, showing that such contaminant mass hotspots may remain largely hidden. Because the estimated PCB stock was of the same order of magnitude as annual upstream PCB inputs previously measured to the estuary, these deposits may constitute a substantial secondary source of contamination if remobilized.
(Journal of Hazardous Materials Advances. vol. 24, n° 2772-4166, pp. 101556, 01/11/2026)
M2C, UNICAEN, NU, INSU - CNRS, UNIROUEN, NU, CNRS, UNIROUEN, NU, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, GEDI, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, Institut CARMeN, UNICAEN, NU, ENSICAEN, NU, UNIROUEN, NU, INSA Rouen Normandie, INSA, NU, INC-CNRS, CNRS, COBRA, IRCOF, UNIROUEN, NU, INSA Rouen Normandie, INSA, NU, CNRS, UNIROUEN, NU, INSA Rouen Normandie, INSA, NU, INC3M, UNICAEN, NU, ENSICAEN, NU, ULH, NU, UNIROUEN, NU, INSA Rouen Normandie, INSA, NU, INC-CNRS, CNRS, INC-CNRS, CNRS
Numerical modelling of barchan dunes along the Aquitaine Coast
Along the Aquitaine coast in Southwest France, a vast barchan dune field is observed which provides an opportunity to study the morphology of such coastal dunes and examine differenthypotheses about their origin and evolution. The dunes formed over the past few centuries and were still shifting in the mid-19th century and were subsequently fixed by planting a maritime pine forest. Traces of their past migration are still visible in the landscape, particularly in the interdune areas where arc-shaped sandy ridges can be observed in low-lying areas. Beyond morphological characterizations, it is important to understand how these landforms have evolved under variable environmental forcing. Barchans are characterized by their crescent shape, however, the dunes examined in this study display characteristics that are specific to the Cap Ferret region, reaching heights of up to 32 m with relatively short horns and rounded shape. In this context, this study utilizes the process-based numerical model AeoLiS to identify the dominant controls on the morphological evolution of such dunes, hindcast the past wind regime conditions that shaped them by validating with the present topography and test the role of water level and vegetation in the formation of the surrounding arc-shaped ridges. For this study, we selected a typical dune morphology of the Cap Ferret Spit. Previous results show that the morphology of these barchans is consistent with a wind regime of directional spreading variability ranging from 30-45 °, and that the formation of the arc-shaped ridges can be explained by the influence of water level variability and vegetation. While previous work on coastal barchan dunes has mainly relied on field observations to propose hypotheses about their evolution, here a process-based aeolian transport model is used to simulate alternative forcing scenarios and validate them with the present-day topography, thus allowing competing hypotheses to be quantitatively tested. This approach sets a precedent for how coastal dune morphology and evolution can be investigated using numerical modelling tools combined with field observations to examine existing hypotheses.
(27/10/2026)
BRGM, TU Delft, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Structures surimposées des dunes aquitaines : description et compréhension des facteurs de mise en place
Le littoral aquitain se caractérise par de vastes champs dunaires s’étendant sur 5-7km à l’intérieur des terres, majoritairement fixés par une forêt de pin maritime. Trois grands ensembles morphologiques peuvent être distingués: i) la dune bordière, façonnée par des actions de gestion depuis le XIXᵉ siècle, ii) les dunes barkhanoïdes, qui s’étendent sur 3-5km vers l’intérieur des terres et iii) les dunes paraboliques, les plus distales. Les dunes barkhanoïdes, sujet de cette étude, présentent une grande diversité de morphotypes correspondant à différents stades de leur développement: forme chaotique de petites dimensions, rides barkhanoïdes ou barkhanes individualisées. On dénombre jusqu’à 7 à 10 séries de dunes, plus ou moins parallèles les unes aux autres, dont la hauteur de crête augmente vers l’intérieur des terres. Au sud du Bassin d’Arcachon, les dunes sont plus massives, accolées en méga-rides-barkhanoïdes, pouvant atteindre localement 70m d’altitude (Biscarrosse). Malgré cette diversité (spatiale, dimensions), on constate que quelques que soit leur forme et leur taille, les dunes barkhanoïdes présentent toutes des structures surimposées. Le LiDAR-HD (©IGN) a permis de révéler ces structures de second ordre sur l’ensemble du littoral Aquitain. Deux types de morphologies sont identifiées (Billieres-Kim et al., soumis): des dépôts surimposés parallèles à la crête (superimposed bedforms) et des structures ondulantes régulières, perpendiculaire à la dune (wavy patterns). Bien que mentionnées dans la littérature, ces structures de 2nd ordre restent peu étudiées, tant du point de vue de leurs dimensions que des processus et conditions prévalents à leur formation. L’approche couplée LiDAR-Géoradar, constitue une approche performante pour étudier ces structures, à la fois en identifiant les caractéristiques de surface et en imageant avec grande précision l’architecture interne des dunes. Par ailleurs, les dunes du Pilat et du Trencat (33) sont deux systèmes dunaires transgressifs actifs, qui présentent des structures de 2nd ordre similaires mais de plus faibles dimensions. La comparaison entre dunes actives et anciennes dunes fixées permettra, par analogie, de s’interroger sur les forçages ayant gouverné leur mise en place au cours des derniers siècles, de replacer l’émergence de ces structures dans l’évolution des systèmes dunaires aquitains, et plus largement de la façade atlantique.
(27/10/2026)
BRGM, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Biomarkers and diatoms as tracers of phytoplankton communities and past sea ice conditions in the southwestern Ross Sea, Antarctica: drivers and variability over the last 200 years
The Ross Sea, Antarctica, is among the most seasonally productive regions of the global ocean, where different classes of phytoplankton, such as diatoms, dinoflagellates, and haptophytes (Phaeocystis antarctica), play key roles in marine ecosystems and the carbon cycle. Sea ice dynamics strongly influence Ross Sea phytoplankton blooms, yet the effects of recent sea ice changes on bloom composition and productivity remain poorly constrained, and longer baseline records are required to understand changes in sea ice and resulting impacts on phytoplankton and climate. The last 200-year period provides a natural baseline before the onset of the warming and rising atmospheric carbon dioxide (CO2) associated with industrialisation, making it critical for contextualising recent and projected change. We used sedimentary biomarkers and diatom assemblages to examine the relationship between physical changes in sea ice and phytoplankton community composition, which in turn influences the chemical signatures preserved in marine sediments. We investigated phytoplankton-derived lipid biomarkers (fatty acids, highly branched isoprenoids; HBIs, sterols) and diatom assemblages in six marine sediment core tops and three short sediment cores collected along a north-south transect extending from McMurdo Sound coastal polynya to south of Terra Nova Bay. Diatoms and biomarkers in core tops reveal increased proportions of open-ocean diatom species and bacterial fatty acids towards the southern end of the transect near McMurdo Sound driven by lower summer sea ice concentration and yearly duration, along with a phytoplankton community dominated by diatoms and higher summer biomass. In contrast, the northern end of the transect, near Terra Nova Bay, is characterised by higher proportions of diatoms associated with sea ice, as well as increased concentrations of sea ice diatom-derived fatty acids, and HBIs, driven by greater sea ice concentrations. Similarly, Phaeocystis antarctica-derived fatty acid biomarkers increase towards the northern end of the transect, likely driven by differences in the phytoplankton community. A Principal Component Analysis (PCA) of the biomarker and diatom dataset confirms this spatial structure, resolving three main variance groupings: diatoms and fatty acids associated with heavier sea ice (Fragilaropsis curta group, C24V0), which are inversely related to open-water and fast ice diatom assemblages (Chaetoceros resting spores, open ocean, cold water, and sea ice diatoms), while fatty acids and HBIs form a third, independent grouping consistent with shared postdepositional degradation. Within the short cores, sea ice associated diatoms such as Fragilariopsis curta and the sea ice proxy, PIPSO25, indicate an increase in sea ice extent over the last 200 years, accompanied by declining open ocean diatom species, a trend not captured by phytoplankton-derived fatty acids alone, which show little change in community composition over the same period. Overall, our records reveal a 200-year increasing sea ice trend in the southwestern Ross Sea, consistent with existing regional sea ice extent reconstructions from ice cores. Biomarkers in the southwestern Ross Sea sediment independently distinguish between pelagic diatoms, P. antarctica, and sea ice-associated diatoms, offering a valuable tool for developing longer decadal resolution records of sea ice and phytoplankton community changes.
(Biogeosciences. vol. 23, n° 1726-4170, pp. 6979 - 7008, 07/10/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Deciphering environmental processes in sedimentary carbonates, a dynamic isotope box model approach
Carbon and oxygen isotope records of sedimentary carbonates (δ13Ccarb and δ18Ocarb) are among the most widely used proxies for paleoenvironmental reconstructions, although their interpretation can be complicated by complex and overprinting processes. Here we present an innovative dynamic box model to unravel the environmental implications of δ13Ccarb and δ18Ocarb, that we apply and constrain in a modern lacustrine setting. We compare the simulated isotopic trends with those measured in the lake sedimentary carbonates over the last 60 years and confront our modeled dissolved inorganic carbon concentrations in the lake with reported measurements for the same period. While most of the relevant environmental parameters of the studied volcanic Lake Alchichica (Mexico) are well constrained, tuning the remaining inputs of the model allows a quantitative assessment of the environmental processes governing the lake's hydrological, carbon and oxygen cycles. Most notably, our results reveal that a clear imbalance in the lake's C budget and δ13C data can only be resolved if the model includes a substantial – but previously unrecognized – volcanic CO2 degassing flux to the lake. Our results further support that groundwater extraction and agriculture in the area have increasingly affected the lake's hydrological and C balance since the 1980s. Overall, we show that this alkaline lake, despite high biological productivity and massive carbonate deposition, is a net CO2 source to the atmosphere. Through a thorough parametrization and characterization of the C and O fluxes in a modern setting, this new modeling approach hold promises for reconstructing ancient environments from carbonate isotope archives.
(Chemical Geology. vol. 721, n° 0009-2541, pp. 123616, 05/10/2026)
BGS, EPHE, PSL, CNRS, UBE, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UNAM, IFPEN, IMPMC, MNHN, SU, CNRS, ESE, CNRS, IPGP - UMR_7154, INSU - CNRS, IGN, UR, IPG Paris, CNRS, UPCité, CARRTEL, USMB [Université de Savoie] [Université de Chambéry], INRAE, Fédération OSUG
Littoral and wetland vegetation decrease carbon emissions from dry inland waters
Lakes are recognized as active components of the inland water carbon (C) cycle, as organic matter is processed by microbial respiration, inducing large carbon dioxide (CO 2 ) and methane (CH 4 ) emissions. In the context of long-lasting drought periods, large uncertainties remain about: (1) the influence of wet-dry cycle on CO 2 and CH 4 fluxes in littoral zones and lacustrine wetlands; and (2) the contribution of emergent vegetation to C fluxes in dry inland waters. At the water-land interface of two shallow lakes, this study focuses on CO 2 and CH 4 fluxes from vegetated and bare dry inland waters in relation to hydrological fluctuations. Three seasonal campaigns were conducted to measure daytime CO 2 and CH 4 fluxes in pelagic, littoral and wetland surface waters, as well as in temporarily air-exposed sediments, using floating and static chambers, respectively. Our results reveal that wet-dry cycle in the littoral zone and wetlands strongly influence gaseous C fluxes through contrasting patterns, especially in late summer, when the biological processes are most active (primary production and respiration). In air-exposed littoral zones, organic-poor sandy sediments presented the lowest CO 2 and CH 4 emissions, whereas in air-exposed lacustrine wetlands, water-saturated sediments accumulated high amounts of plant-derived organic matter, promoting intense microbial activity and the highest C emissions. However, amphiphytes and helophytes vegetation in exposed littoral zones and wetlands reversed the direction of C fluxes, inducing the highest CO 2 uptake due to high photosynthesis rates. This study underlines the relevance of considering vegetation in dry inland waters, particularly in lacustrine littoral zones and wetlands, to obtain comprehensive lake C budgets, especially under climate change scenarios.
(Journal of Environmental Sciences. vol. 168, n° 1001-0742, pp. 656 - 666, 01/10/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UNIPR, UR EABX, INRAE, ECLA, USMB [Université de Savoie] [Université de Chambéry], INRAE, OFB
Land–sea thermal decoupling and iceberg discharges in the western North Atlantic during Heinrich Stadials 5–3
Abrupt climate changes of the last glacial period, including Dansgaard–Oeschger cycles and Heinrich Stadials (HSs), were contemporaneous with profound disruptions of the Atlantic Meridional Overturning Circulation (AMOC). However, their impacts on the western North Atlantic and adjacent North American continent remain poorly resolved. Here we present a high-resolution multiproxy reconstruction from core MD99-2203 (Cape Hatteras, 35° N), integrating mineralogical and reworked dinocyst data, pollen and foraminiferal assemblages, and iLOVECLIM model simulations to identify HSs and investigate vegetation–ocean linkages during HSs 5–3. In contrast to the western European margin, each HS is marked by continental cold conditions coeval with warm sea surface temperatures (SST) and the onset of iceberg-rafted debris (IRD) deposition near Cape Hatteras, yet the regional landscape remained dominated by open forests. A close up of HS 4 reveals a distinct two-phase structure: an early stage of synchronous cooling in land and SST, associated with peak IRD deposition in the Ruddiman Belt, followed by a post-surge phase when ice-rafted debris reached 31–35° N. During this phase, cold and dry continental conditions contrasted with anomalously warm sea surface temperatures, generating enhanced land–sea thermal gradients. This contrast increased humidity and, together with rising atmospheric CO2 concentration, may have triggered transient forest recovery, which coincided with subsequent surface cooling. Comparisons with transient iLOVECLIM simulations successfully capture the early phase and reveal insightful spatially heterogeneous feedbacks in the later period. Our results reveal complex, evolving land–ocean interactions during abrupt climate events, providing new insights into regional climate dynamics and impacts of AMOC weakening.
(Quaternary Science Reviews. vol. 389, n° 0277-3791, pp. 110141, 01/10/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IPMA, CCMAR, UAlg, HNHP, MNHN, UPVD, CNRS
Unraveling bottom current influence on diatomaceous deposits in the Bransfield Strait (Antarctic Peninsula) throughout the past millennium
(Marine Geology. vol. 500, n° 0025-3227, pp. 107837, 01/10/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS