Potential role of giant marine diatoms in sequestration of atmospheric CO2 during the Last Glacial Maximum: δ13C evidence from laminated Ethmodiscus rex mats in tropical West Pacific
Giant marine diatoms, blooming or aggregating within deep chlorophyll maxima under stratified conditions, can generate substantial production and a large export flux of organic carbon from surface waters. However, their role in regulating glacial-interglacial variation in atmospheric pCO 2 remains unclear. Here, we report the organic carbon isotopic compositions of Ethmodiscus rex diatoms (δ 13 C E. rex) and bulk sediments (δ 13 C org) from a sediment core in the eastern Philippine Sea dated to ~19.5-31.0 kyr B.P. and consisting of (from youngest to oldest) (1) laminated E. rex diatom mats (LDM), (2) diatomaceous clay (DC), and (3) pelagic clay (PC). Our results suggest that δ 13 C E. rex provides a better record of palaeoceanographic processes during LDM and DC deposition than δ 13 C org because of reduced differential vital effects in near-monospecific E. rex fractions. We used the isotopic composition of the coarse E. rex fraction (δ 13 C E. rex (>154 μm)) to calculate the CO 2 partial pressure of eastern Philippine Sea surface waters (pCO 2-sw) during the Last Glacial Maximum (LGM). Our pCO 2-sw records suggest that the eastern Philippine Sea switched from being a strong CO 2 source during DC deposition to a weak CO 2 sink during LDM deposition. The role of the eastern Philippine Sea as a CO 2 sink during the LGM was promoted by elevated primary production and, to a lesser extent, intensified water-column stratification. These observations highlight the potential role of giant marine diatoms in the sequestration of atmospheric CO 2 during the LGM and, hence, support changes in biogenic silica fluxes as a potential cause of lower glacial atmospheric CO 2. Our findings are consistent with an eolian source of silica, as proposed by the 'silica hypothesis' and the 'silicon-induced alkalinity pump hypothesis' but not by the 'silicic acid leakage hypothesis.
(Global and Planetary Change. vol. 108, n° 0921-8181, pp. 1-14, 22/04/2026)
IOCAS, CAS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UC
Differences in fluorescence properties between humic acid and its size fractions separated by preparative HPSEC
We applied three dimensional excitation-emission-matrix (3D-EEM) spectrofluorometry to investigate the fluorescence properties of a humic acid (HA) solution at different pH values and its size-fractions separated by preparative high performance size exclusion chromatography (HPSEC). 3D-EEM fluorescence spectra revealed peak maxima in the bulk HA which were assigned to protein-like, phenol-like and naphthol-like components. Moreover, changes of peak maxima with pH showed that phenol-like and naphthol-like molecular classes were composed of sub-components with different acidities, and, thus, different structures. The 3D-EEM spectra of three size-fractions separated by HPSEC showed similar peak maxima as for the bulk HA, with additional components, such as highly condensed aromatic systems, which had not been visible in the bulk HA. Furthermore, the fluorescence intensity of peak maxima in 3D-EEM spectra of size-fractions appeared invariably greater than that for the bulk HA. This phenomenon as well as the appearance of new maxima in size-fraction spectra is explained by the reduced self-quenching effect in the less complex and conformationally looser size-fractions. In fact, the close mutual proximity of fluorescent humic molecules in the tight supramolecular association of the bulk HA decreased or even inhibited their fluorescence quantum yield. This work shows that, due to self-quenching of humic molecules, fluorescence spectroscopy cannot be used to characterise the molecular complexity of humic matter and, thus, differentiate its environmental origin. \textcopyright 2012 Elsevier B.V.
(Journal of Geochemical Exploration. vol. 129, n° 0375-6742, pp. 23--27, 22/04/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Investigations into the differential reactivity of endogenous and exogenous mercury species in coastal sediments
Stable isotopic tracer methodologies now allow the evaluation of the reactivity of the endogenous (ambient) and exogenous (added) Hg to further predict the potential effect of Hg inputs in ecosystems. The differential reactivity of endogenous and exogenous Hg was compared in superficial sediments collected in a coastal lagoon (Arcachon Bay) and in an estuary (Adour River) from the Bay of Biscay (SW France). All Hg species (gaseous, aqueous, and solid fraction) and ancillary data were measured during time course slurry experiments under variable redox conditions. The average endogenous methylation yield was higher in the estuarine (1. 2 %) than in the lagoonal sediment (0. 5 %), although both methylation and demethylation rates were higher in the lagoonal sediment in relation with a higher sulfate-reducing activity. Demethylation was overall more consistent than methylation in both sediments. The endogenous and exogenous Hg behaviors were always correlated but the exogenous inorganic Hg (IHg) partitioning into water was 2. 0-4. 3 times higher than the endogenous one. Its methylation was just slightly higher (1. 4) in the estuarine sediment while the difference in the lagoonal sediment was much larger (3. 6). The relative endogenous and exogenous methylation yields were not correlated to IHg partitioning, demonstrating that the bioavailable species distributions were different for the two IHg pools. In both sediments, the exogenous IHg partitioning equaled the endogenous one within a week, while its higher methylation lasted for months. Such results provide an original assessment approach to compare coastal sediment response to Hg inputs.
(Environmental Science and Pollution Research. vol. 20, n° 0944-1344, pp. 1292--1301, 22/04/2026)
IPREM, UPPA, INC-CNRS, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Tracking atmospheric and riverine terrigenous supplies variability during the last glacial and the Holocene in central Mediterranean
A multiproxy study coupling mineralogical, grain size and geochemical approaches was used to tentatively retrace eolian and fluvial contributions to sedimentation in the Sicilian Tunisian Strait since the last glacial. The eolian supply is dominant over the whole interval, excepted during the sapropel Si when riverine contribution apparently became significant. Saharan contribution increased during the B011ing Allerod, evidencing the persistence of aridity over North Africa although the northern Mediterranean already experienced moister and warmer conditions. The Younger Dryas is marked by proximal dust inputs, highlighting intense regional eolian activity. A southward migration of dust provenance toward Sahel occurred at the onset of the Holocene, likely resulting from a southward position of the Inter Tropical Convergence Zone that was probably associated with a large-scale atmospheric reorganization. Finally, a peculiar high terrigenous flux associated with drastic modifications of the mineralogical and geochemical sediment signature occurred during the sapropel 51, suggesting the propagation of fine particles derived from major floodings of the Nile River resulting from enhanced rainfall on northeastern Africa and their transportation across the Sicilian Tunisian Strait by intermediate water masses.
(Climate of the Past. vol. 9, n° 1814-9324, pp. 1065-1087, 22/04/2026)
LOG, INSU - CNRS, ULCO, CNRS, IRD [Ile-de-France], HNHP, MNHN, UPVD, CNRS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, PALEOCEAN, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, GEOPS, UP11, CNRS
Mise au point d’un indice diatomique pour les cours d’eau de la Réunion (IDR) : Rapport final sur la démarche d’élaboration de l’indice (Version finale, 05-02-2013)
La DCE a force d'application dans les DOM comme dans le contexte continental. Cependant l'environnement abiotique comme les espèces en place constituent un contexte biogéographique très spécifique rendant impossible l'utilisation d'indices biologiques préexistants mis au point pour l'Europe continentale. L’Office de l’Eau de la Réunion a donc décidé de porter un programme spécifique de recherche-développement, mis en ½uvre de 2008 à 2012 par le consortium Asconit Consultants – Irstea (ex-Cemagref). L'étude ayant conduit à la genèse de l'IDR (Indice Diatomique Réunion) s'est appuyée sur l’acquisition d’environ 370 relevés taxinomiques des espèces rencontrées sur place et de données associées de chimie des eaux, obtenues sur un réseau de 56 sites à l'occasion de 5 campagnes de prélèvements de terrain réalisées à 2 saisons différentes. L'analyse de ces données a permis une caractérisation plus ou moins consolidée des préférences écologiques de 343 espèces, le repérage de communautés diatomiques-types caractéristiques de conditions environnementales particulières (naturelles, altérées) et, au final, la mise au point de ce nouvel indice IDR qui mobilise les profils de qualité écologique de 172 espèces suffisamment occurrentes d'eau douce. Cet indice d’un principe de conception original mesure l’altération de la qualité de l’eau à partir du cumul de messages d’altération portés par 48 taxons d’alerte qualifiés de « Taxons –», dont la présence est synonyme indiscutable de dégradation anthropique de l’eau.
(pp. 130, 22/04/2026)
UR REBX, IRSTEA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
An integrated environmental approach to investigate biomarker fluctuations in the blue mussel Mytilus edulis L. in the Vilaine estuary, France
Estuarine areas represent complex and highly changing environments at the interface between freshwater and marine aquatic ecosystems. Therefore, the aquatic organisms living in estuaries have to face highly variable environmental conditions. The aimof this work was to study the influence of environmental changes from either natural or anthropogenic origins on the physiological responses of Mytilus edulis. Mussels were collected in theVilaine estuary during early summer because this season represents a critical period of active reproduction in mussels and of increased anthropogenic inputs from agricultural and boating activities into the estuary. The physiological status of the mussel M. edulis was evaluated through measurements of a suite of biomarkers related to: oxidative stress (catalase, malondialdehyde), detoxication (benzopyrene hydroxylase, carboxylesterase), neurotoxicity (acetylcholinesterase), reproductive cycle (vitelline, condition index, maturation stages), immunotoxicity (hemocyte concentration, granulocyte percentage, phagocytosis, reactive oxygen species production, oxidative burst), and general physiological stress (lysosomal stability). A selection of relevant organic contaminant (pesticides, (polycyclic aromatic hydrocarbons, polychlorobiphenyls) was measured as well as environmental parameters (water temperature, salinity, total suspended solids, turbidity, chlorophyll a, pheopigments) and mussel phycotoxin contamination. Two locations differently exposed to the plume of the Vilaine River were compared. Both temporal and inter-site variations of these biomarkers were studied. Our results show that reproduction cycle and environmental parameters such as temperature, organic ontaminants, and algal blooms could strongly influence the biomarker responses. These observations highlight the necessity to conduct integrated environmental approaches in order to better understand the causes of biomarker variations.
(Environmental Science and Pollution Research. vol. 20, n° 0944-1344, pp. 630-650, 22/04/2026)
IFREMER, LEMAR, IRD, IFREMER, UBO EPE, CNRS, INRA, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UR REBX, IRSTEA, CNRS
Bi-hemispheric forcing for Indo-Asian monsoon during glacial terminations
The drivers of the Indo-Asian monsoon dynamics during terminations have recently emerged as a controversial issue. Cheng et al. (2009. Ice Age Terminations. Science 326, 248–252), using East-Asian speleothem records, proposed a strict northern hemisphere insolation control at the orbital timescale with weak monsoon intervals occurring at terminations. On the contrary, An et al. (2011. Glacial–Interglacial Indian Summer Monsoon Dynamics. Science 333, 719–723), using a record from the Hequing paleolake basin, highlight the importance of the southern hemisphere climate forcings on Indian summer monsoon dynamics at glacial–interglacial timescale. The purpose of this note is to propose an explanation of the weak monsoon intervals at terminations, using a deep sea sediment stack monsoon record. The mechanism involved is linked to interhemispheric interactions, as proposed by An et al. (2011), superimposed to the role of orbital forcing (precession and obliquity parameters). This explanation clarifies the combination of complex drivers acting on the Indo-Asian monsoon dynamic at terminations.
(Quaternary Science Reviews. vol. 59, n° 0277-3791, pp. 1-4, 22/04/2026)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, CLIM, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, GLACCIOS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA
Mobility and fluxes of trace elements and nutrients at the sediment–water interface of a lagoon under contrasting water column oxygenation conditions
The early diagenesis of the major carrier phases (Fe and Mn minerals), trace elements (As, Co, Cr, Hg, MeHg, Ni) and nutrients (RNO 3 , NH þ 4 , RPO 4) and their exchange at the sediment water/interface were studied in the Berre Lagoon, a Mediterranean lagoon in France, at one site under two contrasting oxygen-ation conditions (strictly anoxic and slightly oxic) and at an adjacent site with perennially well-oxygen-ated water. From the concentration profiles of the primary biogeochemical constituents and trace elements of the pore and bottom waters, as well as the total and reactive particulate phases, it was possible to locate and identify the diagenetic reactions controlling the mobility of trace elements in the sediments and quantify their rates by coupling one-dimensional steady-state transport-reaction modelling and thermodynamic speciation calculations. Under oxic conditions and in the absence of benthic organisms, the main redox reactions were well identified vertically in the surface sediments and followed the theoretical sequence of oxidant consumption: O 2 > ΣNO 3/MnO 2 > Fe(OH) 3 > SO4 2-. However, under anoxic conditions, only MnO 2 , Fe(OH) 3 and SO 4 2- reduction were present, and they all occurred at the interface. The main biogeochemical controls on the mobility of As, Cr, Hg, MeHg and Ni in the surface sediments were identified as the adsorption/ desorption on and/or coprecipitation/codissolution with Fe oxy-hydroxides. In contrast, Co mobility was primarily controlled by its reactivity towards Mn oxy-hydroxides. In sulphidic sediments, As, Hg and MeHg were sequestered along with Fe sulphides, whereas Co and Ni precipitated directly as metallic sulphides and Cr mobility was enhanced by complexation with dissolved organic ligands. The fluxes of trace elements at the sediment–water interface are essentially dependent on the localisation of their remobilisation and immobilisation reactions under the interface, which in turn is governed by the ben-thic water oxygenation conditions and kinetic competition among those reaction and diffusion processes. Under oxic conditions, the precipitation of Fe or Mn oxy-hydroxides in the surface sediments constitutes the most efficient mechanism to sequester most of the trace elements studied, thus preventing their diffusion to the water column. Under anoxic conditions the export of trace elements to the water column is dependent on the kinetic competition during the reductive dissolution of Fe and/or Mn oxy-hydroxides, diffusion and immobilisation with sulphides. It is also shown that benthic organisms in the perennially oxygenated site have a clear impact on this general pattern. Based on the extensive dataset and geochem-ical modelling, it is predicted that the planned re-oxygenation of the entire lagoon basin, if complete, will most likely limit or reduce the export of the trace elements from the sediments to the water column and therefore, limit the impact of the contaminated sediment.
(Applied Geochemistry. vol. 31, n° 0883-2927, pp. 35-51, 22/04/2026)
CEREGE, IRD, INRA, AMU, CdF (institution), INSU - CNRS, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IFREMER, PROTEE, UTLN
High-resolution analysis of a tsunami deposit: case-study from the 1755 Lisbon tsunami in southwestern Spain
(Marine Geology. vol. 337, n° 0025-3227, pp. 98-111, 22/04/2026)
GEOLAB, UBP, IR SHS UNILIM, UNILIM, UCA [2017-2020], CNRS, UCA, LMV, UBP, INSU - CNRS, UJM, CNRS, IMTV, UdA, INSERM, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Effect-directed analysis of endocrine-disrupting compounds in multi-contaminated sediment: identification of novel ligands of estrogen and pregnane X receptors
Effect-directed analysis (EDA)-based strategies have been increasingly used in order to identify the causative link between adverse (eco-)toxic effects and chemical contaminants. In this study, we report the development and use of an EDA approach to identify endocrine-disrupting chemicals (EDCs) in a multi-contaminated river sediment. The battery of in vitro reporter cell-based bioassays, measuring estrogenic, (anti)androgenic, dioxin-like, and pregnane X receptor (PXR)-like activities, revealed multi-contamination profiles. To isolate active compounds of a wide polarity range, we established a multi-step fractionation procedure combining: (1) a primary fractionation step using normal phase-based solid-phase extraction (SPE), validated with a mixture of 12 non-polar to polar standard EDCs; (2) a secondary fractionation using reversed-phase-based high-performance liquid chromatography (RP-HPLC) calibrated with 33 standard EDCs; and (3) a purification step using a recombinant estrogen receptor (ER) affinity column. In vitro SPE and HPLC profiles revealed that ER and PXR activities were mainly due to polar to mid-polar compounds, while dioxin-like and anti-androgenic activities were in the less polar fractions. The overall procedure allowed final isolation and identification of new environmental PXR (e.g., di-iso-octylphthalate) and ER (e.g., 2,4-di-tert-butylphenol and 2,6-di-tert-butyl-alpha-methoxy-p-cresol) ligands by using gas chromatography coupled with mass spectrometry with full-scan mode acquisition in mid-polar fractions. In vitro biological activity of these chemicals was further confirmed using commercial standards, with di-iso-octylphthalate identified for the first time as a potent hPXR environmental agonist.
(Analytical and Bioanalytical Chemistry. vol. 405, n° 1618-2642, pp. 2553-2566, 22/04/2026)
INERIS, LPTC, UB, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, IRCM - U896 Inserm - UM1, UM1, INSERM, UM