Turbulence measurements in fluid mud layers of a macrotidal estuary
(22/02/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LEGI, UJF, Grenoble INP, CNRS, LTHE, OSUG, UJF, Grenoble INP, INSU - CNRS, IRSTEA, USMB [Université de Savoie] [Université de Chambéry], CNRS, IRD, INSU - CNRS, INPG, CNRS
Deglaciation and volcano-seismic activity in Northern Iceland : Holocene and Early Eemian
(Geodinamica Acta. vol. 18 (1), n° 0985-3111, pp. 81-100, 22/02/2026)
PBDS, INSU - CNRS, CNRS, LPGN, UN, CNRS, GR, UR, INSU - CNRS, CNRS, MNHN, UPMC, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, PALEOCEAN, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA
The biogeography of major diatom taxa in Southern Ocean sediments
Diatoms from 228 Southern Ocean core-top sediment samples were examined to determine the geographic distributions of 32 major diatom species/taxa preserved in the sediments of three zonally-distinct regions; Sea Ice, Open Ocean and the Tropical/Subtropical. In the first of three papers, 14 species/taxa occurring in the region where sea ice covers the ocean surface on an annual basis are geographically documented. Comparisons are drawn between the diatom abundances on the sea floor, sea ice parameters (annual duration and concentration in February and September) and February sea-surface temperature. Such parameters are commonly used in reconstructing past oceanographic conditions in the Sea Ice and Open Ocean zones. Analysis of the geographic patterns and sea-surface parameter correlations reveals species-specific distributions regulated primarily by sea ice coverage and sea-surface temperature, which support the use of diatom remains for the estimation of these past sea-surface environmental parameters. Comparison with reliable accounts of the 14 species from the sediments or plankton also provides the first glimpses into species-specific ecology and habitat linkages.
(Palaeogeography, Palaeoclimatology, Palaeoecology. vol. 223, n° 0031-0182, pp. 93-126, 22/02/2026)
UTAS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
La matière organique sédimentaire de deux zones d'upwelling sud américaines : évolution des marqueurs.
Ce travail concerne l'étude de matière organique (MO) des sédiments marins des plateformes continentales Brésilienne (Cabo Frio - 23°S; 42°W) et Chilienne (Baie de Mejillones, 23°S; 70,5°W) dans le but de caractériser indépendamment chacun des ces deux systèmes et de comparez leur fonctionnement au cours de L'Holocène de part et d'autre de l'Amérique du Sud. Bien que moins intense que celles d'autres secteurs du monde, la cellule d'upwelling du Cabo Frio est la plus importante de la côte brésilienne. Son contrôle dépend de trois facteurs principaux : (1) la morphologie de la plateforme continentale et l'orientation de la ligne de côte, (2) la position de l'axe du courant du Brésil et (3) le régime des vents. Les événements d'upwelling de cette région ont une très forte signature saisonnière (pendant l'été et l'automne austraux), et sont associés principalement à des vents de E - NE. La Baie de Mejillones est l'une des zones océaniques les plus productives du fait de la présence d'un système permanent d'upwelling. De plus, l'interface eau-sédiment demeure anoxique grâce à la présence de la zone d'oxygène minimum du Pacifique dans cette région. Cette anoxie est renforcée par le grand flux de matériel provenant de la productivité superficielle. Cette haute productivité associée à des eaux de fond anoxique et à une bioturbation limité, est à l'origine des sédiments laminés très riches en MO. Le climat aride environnant inhibe drastiquement l'introduction de matériel terrigène dans la baie limitant ainsi l'apport particulaire à la contribution éolienne. Nous avons abordé l'étude de ces deux systèmes contrastés par l'analyse de la MO préservée dans leurs sédiments. Les interprétations sont basées sur la mesure des teneurs en carbone (C), azote (N) et soufre totaux, des isotopes stables du carbone et de l'azote, des analyses par pyrolyse Rock-Eval ainsi que la détermination et la quantification du palynofaciès. En parallèle, nous réalisons la mesure des abondances relatives en alcénones, molécules dont les proportions permettront d'estimer les températures passées de la surface de l'océan. Le contrôle des âges, effectué par des datations au 14C en cours d'acquisition, doit nous permettre d'estimer les variations qualitatives et quantitatives de la MO sédimentaire au cours du temps. Contrairement aux sédiments laminés de nature plus organique de Mejillones, les sédiments du Cabo Frio visuellement homogènes sont d'origine pélitique et présentent des inclusions de bioclastes carbonatés. Les premiers résultats montrent que la matière organique contenue dans ces sédiments présente une certaine variabilité en quantité et en qualité, ce qui démontre différents modes de fonctionnement de ces upwellings au cours du temps. Au Brésil, les teneurs en carbone organique total (COT) sont relativement faibles (< 1,6 %), les indices d'hydrogène (IH) présentent des valeurs basses (188 mg HC/g COT en moyenne), tandis que les indices d'oxygène (IO) sont élevés (240 mg CO2/g COT en moyenne). A l'opposé, les sédiments chiliens présentent des fortes teneurs en COT (entre 2,5 et 6,1 %) associées à des IH élevés (455 mg HC/g COT en moyenne) et à des faibles IO (153 mg CO2/g COT en moyenne). La MO de Cabo Frio est relativement oxydée et présente une certaine contribution continentale. La MO de la Baie de Mejillones, quant à elle, est bien préservée et les lamines représentent des variations de la composition et des flux de MO qui arrive au sédiments, étroitement liées à des variations de l'intensité de l'upwelling.
(pp. 1, 22/02/2026)
PALEOTROPIQUE, ISTO, INSU - CNRS, UO, CNRS
Structural description of humic substances from subtropical coastal environments using elemental analysis, FT-IR and 13C-solid state NMR data
Elemental composition and spectroscopic properties (FT-IR and CP/MAS 13C-NMR) of sedimentary humic substances (HS) from aquatic subtropical environments (a lake, an estuary and two marine sites) are investigated. Humic acids (HA) are relatively richer in nitrogen and in aliphatic chains than fulvic acids (FA) from the same sediments. Conversely, FA are richer in carboxylic groups and in ring polysaccharides than HA. Nitrogen is mostly present as amide groups and for lake and marine HS the FT-IR peaks around 1640 cm-1 and 1540 cm-1 identify polypeptides. Estuarine HS exhibit mixed continental-marine influences, these being highly influenced by site location. Overall, the data suggest that aquatic and mixed HS are more aliphatic than has been proposed in current models and also that amide linkages form an important part of their structural configuration.
(Journal of Coastal Research. vol. 21, n° 0749-0208, pp. 370--382, 22/02/2026)
UCS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Alkenone and coccolith records of the mid-Pleistocene in the south-east Atlantic: Implications for the $U^{K'}_{37}$ and South African climate
(Quaternary Science Reviews. vol. 24, n° 0277-3791, pp. 1559-1572, 22/02/2026)
UAB, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Morphodynamics of nearshore rhythmic sandbars in a mixed-energy environment (SW France): 2. Physical forcing analysis
The morphology and migration of rhythmic intertidal ridge and runnel systems, and subtidal crescentic bars that border the southwest coast of France were characterized using in situ surveys and maps obtained by remote-sensing methods. The period from 1986 to 2000 was investigated. A total of 35 km of coast was mapped. This data set shows several specificities, the origin of which are examined in the present report using hydrodynamic data. A complete analysis of the influence of wave climate on both the shape and the movements of these rhythmic sedimentary patterns was performed. In addition, SWAN and MORPHODYN-coupled numerical models were used to provide quantification of both wave breaking and longshore currents for wave parameters that were representative of the mean values and of the energetic conditions. This study demonstrated the short time response of intertidal systems to the wave forcing. When the offshore significant wave height ( Hs) was lower than 2.5 m, regular coastal ridge and runnel systems developed in the intertidal zone and migrated in the longshore-drift direction at a rate of 1.7-3.1 m day -1. By contrast, the ridge and runnel system morphology abruptly changed when the Hs exceeded 2.5 m, and after the storm, the typical ridge and runnel rhythmic topography was recovered within 5-9 days. The crescentic bars, which had a convex seaward shape, were affected by waves with Hs values greater than 3 m (slightly less for short waves). Depending on the wave orientation, the crescentic bars moved in the longshore-drift direction at a rate that reached 1 m day -1. The data suggested a slight negative correlation between the mean alongshore length of the crescentic bar and the mean Hs. Finally, it seemed that increasing the wave obliquity with respect to the coast resulted in the flattening of the crescentic bars. Thus, coupling Spot and in situ mapping to hydrodynamic records allow the characterization of coastal morphology and dynamics, with time and space samplings that are particularly well adapted to the little studied alongshore morphodynamics. This approach should improve the difficult parameterization of morphodynamic models in high-energy environments.
(Estuarine, Coastal and Shelf Science. vol. 65, pp. 449-462, 22/02/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Major factors controlling Holocene δ 13 C org changes in a seasonal sea-ice environment, Adélie Land, East Antarctica
In an effort to investigate the controlling factors behind Holocene d 13 C org changes in East Antarctica we report high-resolution down-core records of bulk organic matter carbon isotopic ratios (d 13 C org), diatom census counts, total organic carbon, and biogenic silica content taken from one core recovered in the Adélie Trough. A good correspondence between the d 13 C org record and records of small/large and pennate/centric ratios in many of the core segments indicates that diatom species composition affected Holocene d 13 C org variations, possibly via diatom shape and size effects. Variations in the surface water CO 2 concentration and in the isotopic composition of the source during the Holocene cannot be ruled out although they cannot explain rapid and large-amplitude d 13 C org changes. Within the limit of our investigation, our results argue against active carbon acquisition through a carbon concentration mechanism as evidenced in low-latitude upwelling systems. The bulk organic matter thus represents a mixing of diatom taxa having different fractionation affinity to aqueous CO 2. Our results confirm previous evidence which demonstrates that d 13 C org down-core records should be used with great caution to reconstruct past CO 2 content in surface waters.
(Global Biogeochemical Cycles. vol. 19, n° 0886-6236, pp. GB4029, 22/02/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, CEREGE, IRD, INRA, AMU, CdF (institution), INSU - CNRS, CNRS
A new method for the measurement of biogenic silica in suspended matter of coastal waters: using Si:Al ratios to correct for the mineral interference
Measurement of biogenic silica (BSi) in the suspended matter of estuarine and coastal waters is not trivial because of the interference of lithogenic silica (LSi) that can represent up to 90% or more of the total particulate silica within the water column. Till date, no method has provided a satisfying way to correct this mineral interference when the most common wet-alkaline digestions are used. The most recently published method, Ragueneau and Tréguer (Mar. Chem., 45 (1994) 43–51), presents the disadvantage to be site-specific. In this paper, we present a robust method to measure BSi in all estuarine and coastal waters and correction for LSi interference. It consists of a double wet-alkaline digestion where the filter sample is submitted to a first digestion (0.2 M NaOH, pH 13.3) at 100 °C for 40 min. At the end of this first leach, all the BSi and part of the LSi have been converted into Si(OH)4. Si and Al concentrations ([Si]1 and [Al]1) in the supernatant are analyzed. After rinsing and drying, the filter is submitted to a second digestion, exactly identical to the first one, leading to the determination of the (Si:Al)2 ratio that is characteristic of the silicate minerals present in the sample. The corrected biogenic silica concentration is thus given by [BSi]=[Si]1–[Al]1(Si:Al)2. There are three basic assumptions behind the proposed method: (1) all the Al measured during the first leach is derived from silicate minerals, (2) all the biogenic silica has been digested during the first leach, so the second leach addresses the Si:Al ratio of silicate minerals only, and (3) silicate minerals dissolve during the second digestion exactly as during the first digestion, i.e. with a similar Si:Al ratio. Theoretical considerations and field experiments demonstrate that the above assumptions are accurate. Blanks and repeatability tests indicate that the detection limit ranges from 0.6 to 1.5 nmol of BSi present on the filter and that the uncertainty is close to 10%. This method was successfully applied to more than 200 samples from five different coastal areas, demonstrating the importance of this correction, which can represent up to 92% of the apparent BSi concentration determined after the first digestion.
(Continental Shelf Research. vol. 25, Issues (5-6), n° 0278-4343, pp. 697-710, 22/02/2026)
LEMAR, IRD, IFREMER, UBO EPE, CNRS, VUB, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LDO, INSU - CNRS, UBO EPE, CNRS
Palynology of the northwestern Mediterranean shelf (Gulf of Lions): First vegetational record for the last climatic cycle
Palynology has been performed for the first time on Late Quaternary sediments of the Gulf of Lions. The aim is both to tighten the chronology of seismic profiles in the region, and to elucidate the vegetation of southern France during the Last Climatic Cycle. Four cores, taken on the shelf, mostly record Marine Isotope Stages (MIS) 1 and 2 and part of MIS 3 and MIS 5. The latter sediments might have been preserved in a paleodepression on the emergent shelf between the Rhône and the Hérault rivers. It would explain their preservation against transgression and regression erosions of more recent stages. This study also provides a synthesis of palynological continental data collected during the last 40 years in southern Europe. Preliminary comparisons made between the latter and new marine data demonstrate that refugia of Picea and Abies existed in southern France during MIS 3 and MIS 2. The dynamics of Artemisia, deciduous Quercus and Corylus, Abies and finally Fagus is also reconstructed for the last deglaciation. First results obtained in the Gulf of Lions confirm and complete that synthesis.
(Marine and Petroleum Geology. vol. 22, n° 0264-8172, pp. 845-863, 22/02/2026)
PEPS, UCBL, INSU - CNRS, CNRS, CBAE, UM2, EPHE, PSL, CNRS, LDO, INSU - CNRS, UBO EPE, CNRS