Late Miocene transformation of Mediterranean Sea biodiversity
Understanding deep-time marine biodiversity change under the combined effects of climate and connectivity changes is fundamental for predicting the impacts of modern climate change in semi-enclosed seas. We quantify the Late Miocene–Early Pliocene [11.63 to 3.6 million years (Ma)] taxonomic diversity of the Mediterranean Sea for calcareous nannoplankton, dinocysts, foraminifera, ostracods, corals, molluscs, bryozoans, echinoids, fishes, and marine mammals. During this time, marine biota was affected by global climate cooling and the restriction of the Mediterranean’s connection to the Atlantic Ocean that peaked with the Messinian salinity crisis. Although the net change in species richness from the Tortonian to the Zanclean varies by group, species turnover is greater than 30% in all cases, reflecting a high degree of reorganization of the marine ecosystem after the crisis. The results show a clear perturbation already in the pre-evaporitic Messinian (7.25 to 5.97 Ma), with patterns differing among groups and subbasins.
(Science Advances. vol. 10, n° 2375-2548, 27/09/2024)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Influence of estuarine physical processes in the transport of microplastics: a modelling study in the Gironde estuary
(23/09/2024)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, SIAME, UPPA, MIO, IRD, AMU, INSU - CNRS, UTLN, CNRS
Estimating CaCO3 Content Based on Natural Gamma Ray (NGR) in Deep-Ocean Sediment Cores
We present a simple, quick, and high-resolution (approx.10 cm) method for calculating almost continuous calciumcarbonate (CaCO3) proxy records in deep-marine sediment cores based on the well-known dependence of NGR (natural gamma ray) on sediment clay content. The method used in this study is based on the assumption that sediment composition along the SAT (South Atlantic Transect) consists of two components: carbonate and clay. This assumption is reasonably accurate for the region under investigation. At carbonate-rich Site U1583 (66–97 wt% CaCO3), calculated CaCO3 wt% contents are within 4.18% at 1 standard deviation (r) of geochemical analyses of the CaCO3 wt% contents of discrete samples (measured using a coulometer), while at the more lithologically variable Site U1557 (0.1–92 wt% CaCO3), they are within 15.6% at 1r. Results indicate good to excellent correlations between the NGR- and coulometry-derived datasets, supporting the use of this method for carbonate stratigraphy, paleoceanography, and paleoclimate reconstructions. We provide an equation to derive CaCO3 wt% from NGR based on the SAT datasets. The procedure described below can be used to construct the higher resolution proxy CaCO3 records at other sites worldwide compared to discrete CaCO3 values. This method can assist with shipboard lithology determination and can guide core sampling.
(Stratigraphy. vol. 21, pp. 225-242, 20/09/2024)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Impact of human activities and climate change on estuarine systems: A multi-proxy and Optically Stimulated Luminescence (OSL) dating analysis of Western France estuaries
The middle of the 19th century marked the end of the Little Ice Age and the onset of a global warming period when entering the industrial era. Because of increased human activities, this phenomenon enhanced over the last 50 years, resulting in an acceleration of sea level rise and a multiplication of extreme events (floods, storms). Global climatic change, coupled with the ongoing urban development of coastal areas, had a major impact on the morphosedimentary behaviour of estuarine systems. Here we present results of a nationwide study of the main estuaries on the west coasts of France. The aim of this study is to compare the evolution of their geomorphology over the last two centuries and thus assess the impact of climate change and human activities. Sediment cores were taken in the Somme, Orne (English Channel), Loire and Gironde (Atlantic) estuaries to monitor environmental changes through a multi-proxy analysis. To establish an accurate geochronological frame of the cored successions, standard multi-grain quartz SAR OSL dating has been used in addition to 14C dating on recovered shell material. Three to five OSL samples per core were collected. The quartz OSL signal is very bright and dominated by a fast component, making it suitable for SAR De measurements. The preheat temperature was set at 160°C/10s, in line with the results of thermal transfer and preheat plateau tests. The quality of the etching was confirmed through purity checks, and the protocol used yielded excellent results in a dose recovery test (average measured to given dose ratio = 1.008±0.004, n=78). The completeness of the bleaching process was checked by comparing the quartz OSL ages with K-rich feldspar pIRIR50,180 ages. Quartz OSL signals appear to be sufficiently bleached for the Somme, Orne and Loire rivers, but we cannot be confident about sufficient bleaching of the quartz OSL signal for the Gironde samples (here IR50 ages are few hundred years older than quartz OSL ages). Nevertheless, the top recently buried sediment in the Gironde estuary was dated with quartz to 67±7 years, strongly suggesting that quartz OSL signal was sufficiently bleached at deposition. Our OSL ages are consistent with topo- and bathymetric map analysis, and provide a geochronological framework that underlines a rapid infilling, with rates for example up to 6cm/year in the Loire estuary. The OSL ages cast doubt on 14C ages previously obtained for the Loire and Gironde estuaries. Discrepancies sometimes exceed several hundred years, which highlights the limitation of 14C ages to date inner estuarine sediment successions (Olsen et al. 2017), where sedimentary materials are highly mobile, and underscores the potential advantages of OSL for such studies. These encouraging results should enable a more ambitious campaign using OSL dating to quantify in greater detail the rapid evolution of estuarine environments in response to global change. Olsen, Jesper, Philippa Ascough, Bryan Lougheed, et Peter Rasmussen. 2017. « Radiocarbon Dating in Estuarine Environments ». 141‑70. https://doi.org/10.1007/978-94-024-0990-1_7
(11/09/2024)
M2C, UNICAEN, NU, INSU - CNRS, UNIROUEN, NU, CNRS, DTU, IGN, UCPH, UNICAEN, NU, LPG, UM, UA, INSU - CNRS, CNRS, Nantes univ - UFR ST, Nantes Univ, LPG-ANGERS, LPG, UM, UA, INSU - CNRS, CNRS, Nantes univ - UFR ST, BIAF, UA, NOC, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Ecodynamique des Terres Rares dans les écosystèmes aquatiques : approches pluridisciplinaire et multi-échelle
Les écosystèmes aquatiques sont soumis à de nombreux contaminants, y compris les Terres Rares (REEs), qui forment un groupe cohérent d'éléments aux propriétés physico-chimiques similaires. Au cours des deux dernières décennies, la production et la consommation accrues des REEs pour les technologies modernes ont conduit à leur présence croissante dans les milieux aquatiques. Cependant, des lacunes significatives subsistent qui nécessitent des approches pluridisciplinaires combinant Géochimie et Ecotoxicologie afin de : i) évaluer les cycles géochimiques (distribution, réactivité et devenir) des REEs dans les écosystèmes aquatiques ; et ii) identifier les facteurs et processus contrôlant leurs concentrations dans les organismes aquatiques (biodisponibilité, bioaccumulation). La première partie de ce travail s'est concentrée sur la distribution spatiale et le comportement géochimique des REEs à l'interface continent-océan, principalement en milieu estuarien. L’analyse des concentrations en REEs dissoutes le long d’un profil estuarien dans l’estuaire de la Gironde par condition d’étiage a permis de caractériser le comportement géochimique dans le gradient de salinité avec : (i) un abattement des REEs à faible salinité (S<5), plus importante pour les REEs légères (La, Ce, Pr, Nd) ; (ii) une augmentation des concentrations dissoutes aux salinités intermédiaires (5 (10/09/2024) EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
The effects of a neonicotinoid insecticide, imidacloprid, on the embryo-larval stages of the sterlet sturgeon, Acipenser ruthenus
(03/09/2024)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, UR EABX, INRAE
The contribution of near surface geophysics to measure soil related terroir factors in viticulture: A review
Wine quality is affected by environmental factors in the location where the vines are cultivated, in particular the soil and the climate. Major soil-related factors influencing vine development, yield, and berry composition (and thus wine quality) include soil water availability, soil temperature, and soil nutrients, particularly nitrogen. These can be impacted by soil depth and soil compaction. Mapping these factors with classical field-based methods is constraining and expensive. Near surface geophysics (NSG) can be useful in increasing the resolution of data acquisition and, possibly, its cost. Among these techniques, many are already commercially available, but some of them, including Magnetic Resonance Sounding, Induced Polarization and Spectral Analysis of Surface Waves, require a high degree of expertise for acquisition and processing. These should be further developed in order to enlarge the application possibilities. This article reviews soil-related parameters relevant to terroir expression in vineyards and how these can be measured with NSG techniques.
(Geoderma. vol. 449, n° 0016-7061, pp. 116983, 01/09/2024)
UMR EGFV, UB, Bordeaux Sciences Agro, INRAE, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Biogeochemical cycling of manganese and iron in a macrotidal and hyperturbid estuary subject to flow-driven sedimentation
The study of manganese (Mn) and iron (Fe) cycling in early diagenetic processes in estuaries is crucial for understanding the functioning of these vital ecosystems and predicting their responses to environmental change. The present study investigates the dynamic interplay of Mn and Fe in early diagenetic processes at highly contrasted hydrosedimentary conditions in the Loire estuary, which is very rare and allows a comprehensive framework to understand diagenetic processes in a very dynamic environment. One campaign took place in the Brillantes intertidal mudflat in March 2015 (PV1), while 3 others took place in a muddy riverbed along the navigation channel off the city of Paimboeuf during a decennial flood in February (RR1–4), under moderate discharge in June (RRK-4) and low in August 2021 (RR2–4). The monitored riverbed station was upstream, under and downstream the maximum turbidity zone, respectively. By combining sequential extraction techniques for Mn and Fe in solid phases and pore-water analysis, the study provides insights into the behaviour of these elements in sedimentary environments and reveals their speciation and association with specific mineral phases and forms during different diagenesis stages. The remobilization of Mn and Fe in the surface sediments of the Brillantes mudflat (PV1) allows iron sulphide formation within the upper 50 cm of the sediment column (above the sulphate penetration depth). The deeper layers show other authigenic phases formation, such as the probable precipitation of vivianite below the sulphate depletion depth and progressive precipitation of carbonate at depth, leading to definitive burial and accumulation. At the muddy riverbed, following the exceptional flood in February 2021 (RR1–4), significant sediment erosion occurred unveiling to the water column old and reduced sediments. Sharp pore-water gradients for dissolved Mn, Fe and sulphate indicated the sudden exposure of the old 7Be-free and anoxic sediment to low-salinity, well‑oxygenated water. Despite its dark colour, this sediment showed no authigenic FeS/FeS2 phases. Four months later, changes in the estuarine environment (low river discharge) and the presence of a maximum turbidity zone (TMZ) led to a new deposition of a sediment layer (RRK-4) triggering transient diagenetic reactions. The freshly deposited sediment layer developed important recycling of dissolved Mn, Fe and sulphate above the precedent sediment water interface (SWI) generating a double peak, accompanied by consistently low concentrations of solid Mn and Fe phases specially FeS/FeS2 and Mn bound to FeS/FeS2 compared to PV1. Six months after the flood event, in August (RR2–4), the discernible attenuation of dissolved Mn and Fe peaks and sulphate concentration, indicated a gradual recovery of characteristic sediment profiles with the well-known redox layer succession. Overall, despite important sulphate reduction within sediments from both the river and its adjacent mudflats, pyritization is not a major process for Mn and Fe burial. The intense hydrodynamics of the mid estuary prevents thermodynamical equilibrium between pore-water chemistry and solid phases not allowing pyrite formation while in the calmer conditions of intertidal mudflats, pyrite accumulates in intermediate depths but carbonates and phosphates seem to be the preferential phases of burial probably related to methane production and phosphate availability.
(Chemical Geology. vol. 661, n° 0009-2541, pp. 122182, 01/09/2024)
LPG, UM, UA, INSU - CNRS, CNRS, Nantes univ - UFR ST, Nantes Univ, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, ISTOM, IPREM, UPPA, INC-CNRS, CNRS, CHROME, UNIMES
Role of manganese oxides and oxyhydroxides in phosphate sequestration in natural aquatic environments
Excessive inputs of phosphorus (P) to aquatic environments can lead to eutrophication. Adsorption of phosphate on Fe oxides is one of the main process that can limit P availability. Oxidized forms of Mn have also been suggested to play a role in P trapping. However, although a considerable number of studies have shown the relationships between the geochemistry of Fe and that of phosphates, few studies have attempted to show the direct links between Mn and P. In the present study, we studied the adsorption of phosphate on synthetized Mn(III) and Mn(IV) oxides placed under natural conditions. The aim was to compare the role of Fe and Mn oxides in phosphate adsorption. Two muddy sediments were collected in a river bed at the edge of a large agricultural area. A sandy sediment was collected downstream. A muddy and a sandy sample were taken in a coastal environment. The experiments on phosphate adsorption by sediment and Mn oxides were carried out in slurries containing in situ waters spiked with 10 μM phosphate. Control experiments without Mn-oxide addition showed that the natural sediments tested still had the capacity to adsorb phosphate, in particular due to the presence of reactive Fe(III) oxides, extractable by an ascorbate solution. The addition of Mn(III) and Mn(IV) oxides in much larger quantities than the initial quantity of Fe oxides had little impact on the rate of phosphate adsorption. For both Mn(III) and Mn(IV) oxides, the Mn/P ratio between added particulate Mn and adsorbed P was very high, with values between 260 and 1000. The Fe/P ratio of the iron oxides contained in the slurries was between 6 and 20. On average, the P adsorption capacity of the Fe oxides was 50 times greater than that of the Mn oxides. Manganese oxides are generally less abundant than iron oxides in natural environments. Mn oxides therefore play a minor role in P sequestration compared with Fe oxides. Even if there are environments where Mn oxides can concentrate, the reduction of Mn oxides and subsequent liberation of adsorbed P does not represent a major risk for eutrophication of aquatic ecosystems.
(Chemical Geology. vol. 662, n° 0009-2541, pp. 122231, 01/09/2024)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Subantarctic jet migrations regulate vertical mixing in the Southern Indian
In the Indian sector of the Southern Ocean, the main Antarctic Circumpolar Current (ACC) transport is associated with the subantarctic jet and deviates around several subantarctic islands and volcanic plateaus. This forms regional eddies that are hotspots for productivity, nutrient and CO2 cycling. Though ACC jet migrations related to past climate variations have been reported in previous studies, little is known about their effect on vertical mixing where fronts interact with bathymetry. Here, we investigate past frontal shifts and their impacts on water column structure in the Del Ca˜no Rise, Crozet Archipelago, and Conrad Rise regions over the last 160,000 years by reconstructing surface and subsurface temperatures from siliceous microfossils assemblages in four sediment cores. Our results suggest that the ACC core was displaced equatorward during the last glacial period (70–18 kyrs), away from bathymetric features of the Indian sector of the Southern Ocean. This equatorward shift probably reduced front/bathymetry interactions and, with it, mixing of the upper layer of the ocean in the lee of subantarctic islands and plateaus. We propose that this process participated in the regional isolation of Antarctic Surface Water from deeper water masses. During Marine Isotope Stage (MIS) 5e (132–118 kyrs), an interglacial episode with a warmer-than-modern climate, the reverse situation is reconstructed, whereby the tightening of the ACC fronts against volcanic plateaus probably resulted in enhanced vertical mixing.
(Earth and Planetary Science Letters. vol. 642, n° 0012-821X, pp. 118877, 01/09/2024)
LEMAR, IRD, IFREMER, UBO EPE, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, EPHE, PSL, GSJ, AIST, SFU.ca