Long-term trends and wave climate variability in the South Atlantic Ocean: the influence of climate indices
Linking wave climate variability and trends with climate indices is important to better understand and predict large-scale patterns of wave variability down to wave conditions at the coast. This study investigates such links in the South Atlantic Ocean using 72 years of ERA5 wave hindcast. Different wave parameters are computed, including storm wave statistics, and are further analyzed in terms of long-term trends and interannual changes. Our results indicate that, over the last decades, wave height has been significantly increasing across the entire domain, while extreme events statistics are also increasing, although with more complex spatial variability. The variations of these wave properties are primarily correlated, from low to high latitudes, with the Atlantic Multidecadal Oscillation (AMO), Tropical Southern Atlantic Index (TSA) and Southern Annular Mode (SAM), with different preferred timescales. We think that better understanding and predicting the evolution of these climate indices, including under climate change, will be critical to anticipate coastal hazards in this region.
(Regional Studies in Marine Science. vol. 66, n° 2352-4855, pp. 103131, 01/12/2023)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Significant Impact of Hydrothermalism on the Biogeochemical Signature of Sinking and Sedimented Particles in the Lau Basin
Abstract Iron (Fe) is an essential micronutrient for diazotrophs, which are abundant in the Western Tropical South Pacific Ocean (WTSP). Their success depends on the numerous trace metals, particularly Fe, released from shallow hydrothermal vents along the Tonga Arc. This study aimed to explore the spatio‐temporal impact of hydrothermal fluids on particulate trace metal concentrations and biological activity. To identify the composition of sinking particles across a wide area of the WTSP, we deployed sediment traps at various depths, both close and further west of the Tonga Arc. Seafloor sediments were cored at these deployment sites, including at a remote location in the South Pacific Gyre. The sinking particles were composed of a large amount of biological material (up to 88 mg d −1 ), indicative of the high productivity of the region. A significant portion of this material (∼21 ± 12 wt.%) was lithogenic of hydrothermal origin, as revealed through Al‐Fe‐Mn tracing. The sinking material showed similar patterns between lithogenic and biogenic fractions, indicating that hydrothermal input within the photic layer triggered surface production. A hydrothermal fingerprint was suggested in the sediments due to the high sedimentation rates (>47 cm kyr −1 ) and the presence of large, heterogeneous, metal‐rich particles. The presence of nearby active deep hydrothermal sources was suspected near the Lau Ridge due to the large particle size (1–976 μm) and the significant excess of Fe and Mn (2–20 wt.%). Overall, this study revealed that hydrothermal sources have a significant influence on the biogeochemical signature of particles in the region.
(Journal of Geophysical Research. Oceans. vol. 128, n° 2169-9275, 30/11/2023)
LOV, INSU - CNRS, SU, CNRS, IMEV, INSU - CNRS, SU, CNRS, GET, IRD, UT3, Comue de Toulouse, INSU - CNRS, CNES, CNRS, IMEV, INSU - CNRS, SU, CNRS, MIO, IRD, AMU, INSU - CNRS, UTLN, CNRS, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, CEFREM, UPVD, INSU - CNRS, CNRS
Present and past biogeochemical functioning of the benthic ecosystem of the West Gironde Mud Patch (Bay of Biscay) : remineralization, recycling and burial processes of C and associated elements (O2, N, Mn, Fe, P, S)
In order to improve the understanding of the biogeochemical functioning of River-dominated Ocean Margins (RiOMars), the West Gironde Mud Patch (WGMP) was used as a model of a temperate non-deltaic system subjected to a high hydrodynamics. Measurements and sampling, carried out during eight cruises in different seasons between 2016 and 2021, allowed to characterize its biogeochemical functioning from seasonal to multi-century scales. Results showed that in the proximal area (i.e., < 42.5 m), the high hydrodynamics results in a sediment instability with a surface layer of transient sandy muds (< 10 cm) overlying relic muddy sediments. This induces a digenetic regime divided into two layers, a modern and a relic, having distinct biogeochemical functioning. In the superficial modern layer, organic matter is remineralized through aerobic respiration and suboxic degradation processes. Conversely, sulfate reduction is the main remineralization process occurring in relic deposits. Moreover, measurements of several particulate and dissolved compounds highlighted that the cycles of iron and sulfur differ between relic sediments and the rest of the WGMP. In the distal area, where a more continuous sedimentation occurs, the diagenetic sequence gradually expands seaward, likely due a decrease in organic matter lability and an increase in bioturbation. Seasonal measurements highlighted that aerobic respiration rates vary in response to seasonal events such as the spring blooms and bottom water deoxygenation. On a multi-decennial scale, more than half of the organic carbon deposited in the distal area is buried in sediments with a maximum burial rate of 45 gC m-2 y-1. The organic carbon load of the sediments shows that, this burial is less efficient on a multi-century scale and is mainly related to the grain-size of deposited particles. On this time scale, organic matter remineralization is limited by its lability and bioavailability. Results also highlighted that the WGMP is a sink through the precipitation of authigenic minerals (P, S, Fe, Si) and the adsorption on particles (C, Fe, Mn). Finally, this work has shown that, due to its non-deltaic nature, the biogeochemical functioning of the WGMP differs from that of previously studied high-energy RiOMars, suggesting that it could represent a new RiOMars model.
(27/11/2023)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Role of Atmospheric Indices in Describing Shoreline Variability Along the Atlantic Coast of Europe
AbstractBeaches are highly variable environments and respond to changes in wave forcing, themselves modulated by climate variability. Here, we analyze three high‐quality beach profile data sets to robustly investigate, for the first time, the link between shoreline change, wave forcing and climate variability along the Atlantic coast of Europe. Winter wave conditions are strongly associated with North Atlantic Oscillation (NAO) and Western Europe Pressure Anomaly (WEPA), with WEPA explaining 50%–80% of the winter wave power variability. Shoreline variability during winter is also strongly linked to NAO and WEPA, with WEPA explaining 25% of the winter shoreline variability. Winter wave conditions and associated shoreline variability are both unrelated to El Nino Southern Oscillation. In addition to the atmospherically‐forced beach morphological response, shoreline change also depends strongly on the antecedent morphology as evidenced by significant correlations between summer/winter shoreline response and the shoreline position at the start of each season.
(Geophysical Research Letters. vol. 50, n° 0094-8276, 20/11/2023)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Compréhension des interactions entre l'hydroclimat du Nord-Est du Brésil et l'Atlantique tropical de l'Ouest au cours des derniers 300 000 ans par une approche multi-traceurs organiques
La Terre est un système complexe aux multiples interactions et le lieu de vie d’innombrables espèces vivantes. Dès lors, de nombreux travaux ont permis depuis des décennies, d’améliorer notre compréhension du climat de la Terre. Toutefois de nombreuses zones d’ombre restent aujourd’hui inexplorées. La région du Nord-Est (NE) du Brésil et de l’Atlantique tropical de l’Ouest est à ce jour relativement peu étudiée. Pourtant, l’hydroclimat singulier du NE Brésil et le rôle de l’Atlantique tropical de l’Ouest dans le transport interhémisphérique de chaleur font de cette région une zone importante d’un point de vue climatique. Parmi les traceurs couramment employés pour reconstruire les paléoenvironnements, les biomarqueurs lipidiques sont de précieux supports d’information. De nombreuses propriétés environnementales telles que la température de l’océan, la composition du couvert de végétation ou les conditions hydroclimatiques peuvent être reconstruites à partir de l’abondance, de la distribution ou de la composition isotopique de ces molécules. Ce projet de thèse vise à reconstruire les variations hydroclimatiques passées dans la région de l’extrême NE du Brésil, en relation avec la circulation de surface de l’Atlantique tropical de l’Ouest par la caractérisation du matériel organique d’une carotte de sédiments marins prélevée sur la marge brésilienne qui couvre les derniers 305 000 ans. L’analyse de la matière organique (MO) aux échelles totale et moléculaire a, dans un premier temps, permis de caractériser les sources de MO et notamment la composition des végétations actuelles dans la région d’étude. Ensuite, les températures océaniques de surface et de subsurface, qui ont respectivement été reconstruites à partir de la distribution des alcénones à longues chaînes et des alkyl tétraéthers de glycérols isopréniques, mettent en lumière des réchauffements d’ampleur en subsurface lors des trois dernières déglaciations. L’action conjointe du ralentissement de la circulation océanique et de l’intensification de l’Agulhas Leakage pendant ces périodes est proposée pour expliquer le réchauffement de l’Atlantique tropical de l’Ouest. Enfin, les variations passées du couvert de végétation au NE Brésil, déduites des propriétés des n-alcanes à longues chaînes, sont apparues étroitement liées aux changements hydroclimatiques. La température de surface de l’Atlantique tropical et l’intensité des vents des alizés semblent jouer un rôle majeur dans le contrôle des variations passées de végétation et de l’hydroclimat du Nord-Est du Brésil. En résumé, ce travail a notamment permis d’une part de mieux comprendre le rôle de l’Atlantique tropical en tant que réservoir de chaleur pendant les déglaciations et d’autre part de mieux contraindre les influences contrôlant les variations hydroclimatiques passées au Nord-Est du Brésil.
(16/11/2023)
METIS, EPHE, PSL, INSU - CNRS, SU, CNRS
The Antarctic Ice Core Chronology 2023 (AICC2023) chronological framework and associated timescale for the European Project for Ice Coring in Antarctica (EPICA) Dome C ice core
Abstract. The EPICA (European Project for Ice Coring in Antarctica) Dome C (EDC) ice core drilling in East Antarctica reaches a depth of 3260 m. The reference EDC chronology, the AICC2012 (Antarctic Ice Core Chronology 2012), provides an age vs. depth relationship covering the last 800 kyr (thousands of years), with an absolute uncertainty rising up to 8000 years at the bottom of the ice core. The origins of this relatively large uncertainty are twofold: (1) the δ18Oatm, δO2/N2 and total air content (TAC) records are poorly resolved and show large gaps over the last 800 kyr, and (2) large uncertainties are associated with their orbital targets. Here, we present new highly resolved δ18Oatm, δO2/N2 and δ15N measurements for the EDC ice core covering the last five glacial–interglacial transitions; a new low-resolution TAC record over the period 440–800 ka BP (ka: 1000 years before 1950); and novel absolute 81Kr ages. We have compiled chronological and glaciological information including novel orbital age markers from new data on the EDC ice core as well as accurate firn modeling estimates in a Bayesian dating tool to construct the new AICC2023 chronology. For the first time, three orbital tools are used simultaneously. Hence, it is possible to observe that they are consistent with each other and with the other age markers over most of the last 800 kyr (70 %). This, in turn, gives us confidence in the new AICC2023 chronology. The average uncertainty in the ice chronology is reduced from 1700 to 900 years in AICC2023 over the last 800 kyr (1σ). The new timescale diverges from AICC2012 and suggests age shifts reaching 3800 years towards older ages over marine isotope stages (MISs) 5, 11 and 19. But the coherency between the new AICC2023 timescale and independent chronologies of other archives (Italian Lacustrine succession from Sulmona Basin, Dome Fuji ice core and northern Alpine speleothems) is improved by 1000 to 2000 years over these time intervals.
(Climate of the Past. vol. 19, n° 1814-9324, pp. 2257 - 2286, 10/11/2023)
LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, GLACCIOS, LSCE, UVSQ, INSU - CNRS, CNRS, DRF (CEA), CEA, IGE, IRD, INSU - CNRS, CNRS, INRAE, Fédération OSUG, UGA, Grenoble INP, UGA, AARI, Roshydromet, TECLIM, ELI, UCL, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, NBI, UCPH, OCCR, UNIBE, USTC
Comparison of the accumulation and effects of copper pyrithione and copper sulphate on rainbow trout larvae
(Environmental Toxicology and Pharmacology. vol. 104, n° 1382-6689, pp. 104308, 01/11/2023)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Distribution of Living Benthic Foraminifera in the Baffin Bay and Nares Strait in the Summer and Fall Periods: Relation with Environmental Parameters
Arctic climate warming leads to drastic changes in sea ice dynamics, hence impacting primary productivity but also the benthic communities. Therefore, to assess the response of living benthic foraminifera to contrasting Arctic environments, surface sediments from nine stations were collected during the summer of 2014 and fall of 2015 in the Baffin Bay and Nares Strait. Living standing stock are systematically low in the eastern and western Baffin Bay and much higher in the North Water Polynya and the Kane Basin located at the entrance and in the center of Nares Strait, respectively. High living benthic foraminiferal densities in the NOW reflect higher TOC while the highest density in the Kane Basin coincides with lower TOC but higher C/N and higher δ13Corg. The contribution of agglutinated species is on average very high for the whole study area and dominated by the species Adercotryma glomeratum, Lagenammina arenulata, and Reophax scorpiurus. Calcareous species, dominated by Nonionellina labradorica and Melonis barleeanus, are more abundant in the North Water Polynya and the Kane Basin. The very high living standing stock observed in the Kane Basin might be related to the northern position of the ice arch that summer during 2014 and therefore a particularly scarce sea ice cover might have allowed massive phytoplankton production during that season. In this study, the distribution of living benthic foraminifera is discussed according to several environmental parameters such as water masses, phytoplankton productivity, and organic matter fluxes.
(Journal of Marine Science and Engineering. vol. 11, n° 2077-1312, pp. 2049, 01/11/2023)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, BEEP, IFREMER, UBO EPE, CNRS
Spatial distribution of anthropogenic particles and microplastics in a meso-tidal lagoon (Arcachon Bay, France): A multi-compartment approach.
Assessment of microplastic (MP) contamination is still needed to evaluate this threat correctly and tackle this issue. Here, MP contamination was assessed for a meso-tidal lagoon of the Atlantic coast (Arcachon Bay, France). Sea surface, water column, intertidal sediments and wild oysters were sampled. Five different stations were studied to assess the spatial distribution of the contamination. Two were outside of the bay and three were inside the bay (from the inlet to the back). A distinction was made between all anthropogenic particles (AP, i.e. visually sorted) and MP (i.e. plastic polymer confirmed by ATR-FTIR spectroscopy). The length of particles recovered in this study ranged between 17 μm and 5 mm. Concentration and composition in sea surface and water column samples showed spatial variations while sediment and oyster samples did not. At outside stations, the sea surface and the water column presented a blended composition regarding shapes and polymers and low to high concentrations (e.g. 0.16 ± 0.08 MP.m and 561.7 ± 68.5 MP.m, respectively for sea surface and water column), which can be due to coastal processes and nearby input sources. The inlet station displayed a well-marked pattern only at the sea surface. High AP and MP concentrations were recorded, and fragments along with polyethylene overwhelmed (respectively 76.0 % and 73.2 %). Higher surface currents could explain this pattern. At the bay back, AP and MP concentrations were lower and fibers were mainly recorded. Weaker hydrodynamics in this area was suspected to drive this contamination profile. Overall, fragments and buoyant particles were mainly detected at the sea surface while fibers and negatively buoyant particles prevailed in other compartments. Most of the studied samples presented an important contribution of fiber-shaped particles (from 31.5 % to 94.2 %). Finally, contamination was ubiquitous as AP and MP were found at all stations in all sample types.
(Science of the Total Environment. vol. 898, n° 0048-9697, pp. 165460, 01/11/2023)
EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS
Écoulements Turbiditiques Volcanoclastiques Récents du Bassin de Somalie : Sources et Origines
L'Archipel des Comores se situe au Sud du Bassin de Somalie et est constitué de 4 iles volcaniques. Au large de celui-ci, des dépôts volcanoclastiques ont été découverts à partir d'enregistrements sédimentaires carottes (campagnes océanographiques : MOZAPHARE, 1996 ; SISMAORE, 2020-21 ; SCRATCH, 2021). Ce sont des turbidites à matériel volcanoclastique retrouvées sur plusieurs dizaines à centaines de kilomètres. Cette étude s'insérant dans le cadre des ANRs COYOTE (ANR-19-CE31-0018) et ITCH (ANR-22-EDIR-0003), vise à caractériser les genèses et mécanismes de mise en place des évènements turbiditiques depuis 1200 ka du bassin de Somalie. Pour retracer les sources, des analyses géochimiques ont été faites sur des verres juvéniles basaltiques à basanitiques issus des niveaux volcanoclastiques. Ces derniers ont été étudiés à partir d'une approche morphogranulométrique ayant pour but de (i) classer les grains entre les éléments lithiques masqués et les verres frais et de (ii) décrire des morphologies caractéristiques de certains dynamismes éruptifs. Parmi les douze évènements principaux étudiés, la plupart présente une source potentielle du volcan principal de l'ile de Grande Comore, le Karthala. Les morphologies des particules volcaniques semblent mettre en jeu du volcanisme phréatomagmatique, sous-marin peu profond à surtseyen. Les valeurs de teneurs en eau des verres frais viendraient corroborer cette hypothèse. Une période éruptive principale entre 1200 et 800 ka est documentée dans toutes les carottes étudiées (espacées de 50 à 400 km d'une source comorienne). Pour expliquer une activité volcanique surtseyenne répétitive visible sur plusieurs niveaux espaces de dizaines de milliers d'années, une cyclicité des phases éruptives entrecoupées d'effondrements successifs de l'édifice volcanique, peinant à dépasser durablement la surface et nécessaire à son émersion, sont proposés. Les volumes déplacés avec les turbidites volcanoclastiques font de ces éruptions menant à l'émersion du Karthala des évènements régionaux majeurs.
(30/10/2023)
BRGM, EPOC, EPHE, PSL, UB, INSU - CNRS, CNRS, LMV, IRD, INSU - CNRS, CNRS, UCA, LMV-ENSMSE, Mines Saint-Étienne MSE, IMT, CNRS, LMV, IRD, INSU - CNRS, CNRS, UCA, LGSR, UR, IPG Paris