French Research Institute for Exploitation of the Sea
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Antarctic circumpolar current evolution and its relation to southern hemisphere westerly winds during the holocene
No full textThe Antarctic Circumpolar Current (ACC), Earth’s largest ocean current system, significantly influences global ocean circulation and climate. Despite its importance, the driving forces behind the ACC remain largely elusive. This study, utilizing simulation data combined with reconstructed data, explores the ACC’s evolution and its relationship with the Southern Hemisphere Westerly Winds (SWW) during the Holocene. Both simulation and reconstruction results indicate that the ACC strengthened and shifted poleward during the Holocene. Concurrently, the SWW also intensified and migrated poleward. The ACC’s increasing trend is driven by two ways related to the increase in Southern Hemisphere (SH) temperature. One way operates in the ocean, where rising SH mid-latitude seawater temperature lead to sea ice melt. Consequently, seawater salinity and density decrease. Simultaneously, the south-to-north gradient of salinity and density increases, thereby strengthening the ACC during the Holocene. The other way operates in the atmosphere, where raises SH mid-latitude surface temperature. Simultaneously, sea level pressure decreases. However, the south-to-north gradient of both surface temperature and sea level pressure intensify. These enhanced gradients lead to increased wind stress, which intensifies the SWW and induces a poleward shift. The intensified SWW further amplify the ACC and drive its poleward migration during the Holocene. In summary, the ACC’s strengthening during the Holocene resulted from rising SH temperatures, which altered the meridional gradients of seawater temperature, salinity, and density in the ocean. Concurrently, intensified atmospheric temperature and pressure gradients amplified wind stress and the SWW, further reinforcing the ACC
Soft Gripper for deep sea delicate sampling
No full textThis article focuses on the design of a delicate sampling tool for underwater vehicles. The objective is to develop a device capable of collecting fragile samples without causing damage. Designed for deep-sea exploration at depths of up to 6000 meters, this system aims to overcome the limitations of the bucket scoop grippers currently in use
Persistent organic pollutants in food systems: A comparative study across four contrasting socio-ecosystems: Portugal, Senegal, French Guiana, and Guadeloupe
No full textThis study quantifies persistent organic pollutants (POPs) in food across four territories undergoing dietary transitions: French Guiana, Guadeloupe, Senegal, and Portugal. A total of 200 local and imported food samples from 12 categories were analyzed for polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), and polychlorinated biphenyls (PCBs). Concentrations varied by food matrix, region, and origin. The highest PCDD levels were found in butter from Senegal (16.64 pg/g), and the highest PCDFs in leafy vegetables from Portugal (2.4 pg/g). Fish category showed the highest levels of dioxin-like PCBs (600.7 pg/g) and non-dioxin-like PCBs (3.6 ng/g). All values complied with EU Regulation 2023/915. To estimate dietary exposure, the maximum allowable daily intake (g of food/day) was calculated using Toxic Equivalents (TEQ), EFSA's tolerable weekly intake (TWI: 2 pg TEQ/kg bw/week), and compared to national food consumption data. In Portugal, exposure from fish exceeded the TWI, highlighting the influence of regional contamination sources and dietary habits
Disentangling relative controls of landscape evolution and spatial heterogeneity in the Vaigai River Basin, southern India: Regional implications and applicability
No full textDeciphering tectono-climatic-lithological and other controls over landscape evolution at variable spatiotemporal scales is paramount in natural resources management and development. We have systematically documented and analysed selected critical quantitative morphometric data, namely, asymmetry factor, hypsometric integral, hypsometric curve, drainage divide migration and normalised steepness index, in addition to the assessment of longitudinal profiles and knickpoints, for a unique morphological river basin, the Vaigai River Basin, located in southern India. The spatial variability of various controls of geomorphological characteristics of the basin is interpreted using these morphometric parameters and field data. Notable results include, predominance of a concave-up nature of the majority of the sub-basins, occurrence of a distinct convex zone in the upper part and a distinctly concave zone in the lower part of the basin, a range of symmetric to asymmetric topographic nature with very prominent asymmetry in the middle of the basin, highest normalised channel steepness in the northernmost sub-basin and insignificant and lesser steepness in the majority of the basin, evidence of north-easterly migration of drainage divides within the river basin, manifested by sub-basin boundaries and the alignment of the majority of the knickpoints parallel to the NE–SW trending Karur-Kambam-Painavu-Thrissur shear zone. The results cumulatively indicate that the Vaigai River that runs on an antecedent basin continues evolving, principally under the controls of regional Precambrian structures. Nevertheless, the evolution has been episodic and spatially varied. The resurgent tectonic influence is more pronounced in the northern and north-western parts of the basin, while the river capture and drainage divide migration are pronounced in the northeastern part, signifying the collective influence of tectonics and climate. On the contrary, the middle and lower reaches of the basin lack a soil-sediment-weathered zone, signifying the prevalence of an intense erosional phase of the river. This information, together with previously documented catastrophic flooding events and sediment accumulation, categorise the river basin as episodically active, and in a transient phase of evolution. While providing affirmative evidence for the previous regional geomorphological model, the interpretation of the continuum of inherited Precambrian structures in the present study implies that there are subtle spatial differences of lithological-climatological and structural controls within and among each of the sub-basins that need to be considered for any natural resources management at local to regional scales
Deep Argo Observations of Buoyancy Redistribution in the Atlantic Overturning
No full textThe steady‐state buoyancy budget of the Atlantic Meridional Overturning Circulation (AMOC) balances water mass transformation with meridional export. Using historical ocean data, Deep Argo observations, and atmospheric reanalysis, we assess the residual of this balance—water mass volume trends—and its role in the transformation budget of the Subpolar North Atlantic and Nordic Seas on interannual to bidecadal timescales. On long timescales, volume trends in deep convective seas can be large but the volume expansion or contraction of the upper and lower AMOC limbs remain minimal, suggesting that water mass transformation and AMOC intensity may be interchangeable. Conversely, interannual trends are larger across all regions and all density ranges. The volume of the AMOC limbs is significantly impacted so relationships with transformation rates can only be established when considering the timescales of the southward export of transformed water masses out of the subpolar domain
A new tektite strewn field in Australia ejected from a volcanic arc impact crater 11 Myr ago
No full textThis study re-evaluates the anomalous subgroup of australites known as high Na/K (HNa/K) tektites (Chapman and Scheiber, 1969). Although previous compositional and isotopic analyses suggested a distinct origin, the group has never been formally recognized as a separate tektite strewn field. We present new data from six HNa/K tektites, complementing the eight specimens already described. We conducted a comprehensive investigation, including petrographic (optical and electron microscopy, and micro-X-ray tomography), geochemical (major and trace element compositions, Sr-Nd isotopic composition, 40Ar/39Ar dating), and spectroscopic (for the identification of inclusions) analyses. We concluded that the HNa/K tektites originated from a separate impact event compared to Australasian tektites; they have an andesitic to dacitic composition and arc-related trace element signatures. Lechatelierite (and phosphate) inclusions as well as high levels of chondritic contamination support an impact origin, for which we provide a more precise 40Ar/39Ar age: 10.76 ± 0.05 Ma. For now, Sr-Nd isotopic data and trace elements composition point to three possible sources associated with active volcanic arcs: Luzon (Philippines), Sulawesi (Indonesia), and the Bismarck region (Papua New Guinea). Systematic petrographic and geochemical differences observed between tektites from the western and eastern parts of the ∼900-km-wide hypothesized strewn field (located in Southern Australia) may help to constrain the location of the source crater, but they need to be confirmed by the study of more specimens. We propose the name “Ananguite” for this new group of tektites
Spatiotemporal scales of mode water transformation in the Sea of Oman
No full textIn the Sea of Oman, mode water forms at the surface and is trapped under a warm stratified layer in summer. This capped and well-mixed oxygenated layer decouples the oxygen minimum zone from ocean surface processes and provides a space for remineralisation, reducing oxygen demand in the deeper oxygen minimum zone. Several physical processes, from isopycnal and diapycnal mixing to advection, transform mode water and change its properties. Using monthly climatologies derived from profiling floats and high-resolution underwater glider observations, we perform a volume budget analysis to investigate the mechanisms driving mode water volume change in the Sea of Oman from monthly to 3-day temporal scales. Isopycnal and diapycnal water-mass transformations are estimated in a density-spice framework. Mode water predominantly transforms along isopycnals, yet strong but transient diapycnal transformation occurs at shorter timescales. Moreover, fluxes between the mode water layer and its surroundings are highly sensitive to the presence of mesoscale eddies. Across eddies, diapycnal and isopycnal transformations intensify by 61 % and 45 % respectively, compared to non-eddy conditions, indicating that eddies are drivers of both lateral and vertical water mass exchanges. This study provides a new methodological approach to understanding water mass transformation using high-resolution underwater gliders, and shows that this water mass transformation framework can be used at higher resolution than traditional climatological products or models. By comparing monthly climatological products to the high-resolution glider data, we estimate that the climatological estimates are outside of the high-resolution glider mean ± standard error 40 % of the time for diapycnal and 60 % of the time for isopycnal transformation. These results highlight the intense variability occurring at small scales and can serve to inform future estimates of water mass transformation uncertainty from coarser products
Spatiotemporal Analysis of Sea-Surface pH in the Pacific Ocean Based on Interpretable Machine Learning
No full textIncreasingly severe ocean acidification (OA) disrupts the balance of marine ecosystems. Seawater pH is a key indicator of OA but remains challenging to characterize due to sparse and limited in situ observations. In this study, we propose a spatiotemporal inversion method for surface pH based on interpretable machine learning. By applying carbonate system calculations, we construct an expanded pH observational dataset and obtain spatiotemporal distributions of pH and its influencing factors across the Pacific Ocean from 2003 to 2021. The interpretability analysis reveals that physical, biological, and optical factors contribute 53.9%, 23.9%, and 22.2%, respectively, to pH variability. Sea-surface temperature is the dominant driver, contributing 15.9% of all factors by regulating CO2 solubility and biological activity. Particulate inorganic carbon (PIC) and particulate organic carbon (POC) show relative contributions of 12.6% and 9.4%, respectively, quantitatively reflecting the important roles of biogenic calcification and the biological carbon pump. Furthermore, the analysis focusing on the Ni & ntilde;o 3.4 region reveals a potential pathway through which the ENSO disturbances may affect pH by influencing PIC and POC. Therefore, this study provides a data-driven approach to gain deeper insights into the spatiotemporal patterns of pH and its influencing factors
Variable organic matter stoichiometry enhances the biological drawdown of CO2 in the northwest European shelf seas
No full textVariations in the elemental ratios of carbon, nitrogen, and phosphorus in marine organic matter (OM) and their influence on the marine carbon cycle remain poorly understood for both the open and coastal oceans. Observations consistently show an enrichment of carbon and a depletion of phosphorus relative to elemental Redfield ratios. However, many biogeochemical models are constrained to Redfield stoichiometry, neglecting the effects of variable stoichiometry on carbon cycling and typically underestimating biological carbon fixation. This impedes the accurate representation of OM cycling and the resulting carbon fluxes, especially in productive temperate shelf seas such as the northwest European shelf seas (NWES). Here, the efficiency of oceanic CO2 uptake strongly depends on the biological uptake of inorganic carbon and its export to the North Atlantic, both of which are influenced by OM stoichiometry. In this study, we provide a first comprehensive and quantitative assessment of the effects of variable OM stoichiometry on carbon cycling in the NWES. For this purpose, we integrate two pathways for variable OM stoichiometry, motivated by observational and experimental results, into the regional high-resolution coupled 3D physical-biogeochemical modeling system SCHISM-ECOSMO-CO2 (Semi-implicit Cross-scale Hydroscience Integrated System Model - ECOSystem MOdel): first, the release of carbon-enriched dissolved OM under nutrient limitation and, second, the preferential remineralization of organic nitrogen and phosphorus. With these extensions we reproduce the observed OM stoichiometry and evaluate its impact on marine carbon cycling, with a focus on OM cycling and the resulting air-sea CO2 exchange. Compared to the reference simulation with fixed Redfield stoichiometry, the variable stoichiometry configurations show an increase in the annual net CO2 uptake of 10 %-33 % in the North Sea and 9 %-31 % in the entire NWES, depending on the relative contribution of the two new implementations. As the main driver of the additional CO2 uptake, we identify a corresponding intensification of annual and seasonal OM cycling, resulting in higher net autotrophy in surface waters and higher net heterotrophy in sub-surface layers. This enhanced gradient in net community production leads to an increased biological drawdown of inorganic carbon, most pronounced in the Norwegian Trench. By increasing the biological control on the surface partial pressure of CO2, this leads to higher summer and lower winter uptake. Our results highlight the importance of variable stoichiometry for an accurate representation of the shelf carbon pump mechanism in the NWES, as it significantly influences the efficiency of carbon sequestration. Since the response depends largely on regional physical conditions and pre-existing carbon export mechanisms, regional assessments are essential to understand the sensitivity of the carbon cycle to OM stoichiometry, which should be included in global models to accurately represent the coastal carbon cycle
A surface ocean pCO2 product with improved representation of interannual variability using a vision transformer-based model
No full textThe ocean plays a crucial role in regulating the global carbon cycle and mitigating climate change, with the spatial distribution and temporal variations of ocean surface partial pressure of CO2 (spCO2) directly determining the air-sea CO2 flux. However, constructing a global spCO2 data product that is able to resolve interannual and decadal variability remains a challenge due to the spatial sparsity and temporal discontinuity of observational data. This study presents an approach based on the Vision Transformer (ViT) model, combining high-quality observational data from the CO2 Atlas (SOCAT) with multiple advanced global ocean biogeochemical models results to reconstruct a global monthly spCO2 dataset (SJTU-AViT) at 1° resolution from 1982 to 2023. The approach employs the self-attention mechanism of the ViT model to enhance the modeling of the spatial and temporal variations of spCO2, as well as incorporates physical-biogeochemical constraints from the derivative of spCO2 with respect to key controlling factors as additional features. The incorporation of advanced ocean biogeochemical models during the training process allows the ViT-based model to capture more accurate spCO2 variability in these data-sparse regions. Evaluations demonstrate that the new data product effectively captures spCO2 variability at both global and regional scales, showing good consistency with SOCAT observations, long-term ocean station data, and global atmospheric CO2 trends. The reconstructed spCO2 demonstrates strong capability in reproducing spCO2 anomalies during El Niño-Southern Oscillation (ENSO) events, particularly in the eastern Pacific Ocean, where it shows a correlation of 0.81 with the Niño 3.4 index and demonstrates high consistency with cruise data. Based on the SJTU-AViT dataset, the estimated global air-sea CO2 flux patterns are consistent with known regional features such as strong uptake in the Southern Ocean and outgassing in the tropical Pacific. This study not only provide a new 42-year data product for advancing understanding of the ocean carbon cycle and global carbon budget assessments, but also introduces a new Transformer-based deep learning framework for Earth system data reconstruction. The data product is publicly accessible at https://doi.org/10.5281/zenodo.15331978 (Zhang et al., 2025) and will be updated regularly