French Research Institute for Exploitation of the Sea
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Origin, size distribution, and hygroscopic properties of marine aerosols in the southwestern Indian Ocean: results of six campaigns of shipborne observations
No full textThis study presents observations of marine aerosols made during six ship-based campaigns in the southwestern Indian Ocean in 2021 and 2023. A set of aerosol measurement instruments is used to study the spatial and temporal variability in the number and size distribution of marine aerosols, the concentration of cloud condensation nuclei (CCN), and the hygroscopic properties of aerosols (kappa–Köhler parameter, κ). It has been shown that the number of submicron aerosols measured varies much more significantly (ranging from 100 to over 3000 cm−3) than the number of CCN (60 to 500 cm−3 at 0.4 % supersaturation). As a result, the κ values obtained show considerable variability, ranging from 0.05 to 0.7. Four distinct scenarios are examined to elucidate some of these variations: (1) the predominance of pristine air masses in the eastern regions of the subtropical Indian Ocean, with highly variable κ values sensitive to the low aerosol concentration measured in this area; (2) the predominance of polluted air masses in the Mozambique Channel, with weakly hydrophilic aerosols; (3) a precipitation and storm event in the southern Indian Ocean, with highly variable κ values; and (4) a new particle formation event in the open ocean, with an increase in κ values as the newly formed particles grow to Aitken mode particles. The size distribution of the sampled marine aerosols was analyzed according to the origin of the air masses. In general, a shift of the Aitken and accumulation modes toward larger aerosol sizes was observed for continental and subtropical air masses in the Indian Ocean due to aging. Conversely, the modes shifted toward smaller sizes for air masses in the southern Indian Ocean due to higher primary marine emissions. Aerosols are more hydrophobic for continental air masses (κ ∼ 0.1), more hydrophilic and variable over the subtropical Indian Ocean (κ ranging from 0.2 to 0.6), and intermediate (κ ∼ 0.2) over the southern Indian Ocean. The κ of the subtropical Indian Ocean increases with wind intensity, while it remains stable in the southern Indian Ocean. This effect is attributed to the high proportion of primary organic matter, which is due to the important concentration of nanophytoplankton in the southern Indian Ocean. It has been shown that primary organic aerosols act as surfactants, thus counterbalancing the highly hydrophilic properties of NaCl
Integrating marine protected areas and spatial fisheries restrictions in ecosystem models of the Aegean Sea
No full textThe Mediterranean Sea faces significant ecological challenges, including overexploitation and climate change, that necessitate innovative management strategies. Marine Protected Areas (MPAs) serve as critical management measures in preserving biodiversity and rebuilding fish stocks. This study employed the ECOSPACE modelling framework to assess the impacts of various spatio-temporal management scenarios in the Aegean Sea, focusing on biomass, catches, and spatial distributions of marine populations. The reference scenario revealed a 6 % decline in total biomass and substantial decreases in commercially important species by 2050. While prey species at lower trophic levels showed biomass increases due to reduced predation, these gains were inconsistent across functional groups (FGs). Five scenarios explored MPA placement, extended protection within Natura 2000 areas, and offshore wind farm (OWF) integration. Results demonstrated localized biomass increases within restricted zones but highlighted trade-offs, including effort redistribution and reduced total catches in some cases. Larger MPAs with stricter protections yielded more pronounced ecological benefits, particularly for demersal and benthic species, but posed economic challenges for fisheries. Among the tested scenarios, Scenario 3, which extended the bottom trawling and purse seining restriction area, demonstrated the highest biomass gains for key commercial species with moderate trade-offs in catch, making it suitable for fisheries-focused management. In contrast, Scenarios 1 and 2, which prohibited fisheries within Natura 2000 areas, offered broader conservation benefits, supporting their use in biodiversity-driven strategies. Once in operation, the areas associated with OWFs provided modest conservation benefits, supporting the potential for multi-use marine spatial planning. The findings of the present work can provide valuable insights for policymakers, aiding the development of adaptive management plans that balance biodiversity conservation with sustainable fisheries in the Aegean Sea. Future improvements should integrate high-resolution spatial data and socioeconomic analyses for a holistic understanding
Wind-Driven Control of Shelf-Sea CO2 Sinks
No full textContinental shelf surface waters are considered a variable but increasing sink of atmospheric carbon dioxide (CO2), but the mechanisms controlling these increasing sinks are unclear. We identify that the winter wind‐driven surface atmosphere‐ocean CO2 gas exchange and wind‐driven movement of water onto (or off of) shelf seas are consistent with the atmospheric CO2 uptake tendency of many shelf seas. A 20‐year observational‐based analysis shows that geostrophic, wind and wave driven currents all contribute to the surface shelf break water velocities, but the dominance of each is location and season dependent. Analyzing these flows for fourteen shelf‐seas based on their 20‐year long‐term gradient in air‐sea partial pressure of carbon dioxide (their atmospheric CO2 uptake tendency) identifies significant relationships between uptake tendency and winter (r2 = 0.72 ± 0.03, p < 0.01, n = 14) and autumn (r2 = 0.57 ± 0.05, p < 0.01, n = 14) wind‐driven surface flows. These signals are most strong in winter, but the results are consistent at annual scales. Including the wintertime wind‐driven air‐sea CO2 gas exchange further enhances this result, and collectively they describe 82% of the variance in the atmospheric CO2 uptake tendency data (r2 = 0.82 ± 0.06, p < 0.01, n = 14). These findings identify that long‐term wind‐driven water flow and surface gas exchange are key mechanisms for controlling their chemical evolution and their status as CO2 sinks. This observational‐based evidence highlights the need for these wind‐driven processes to be resolved within methods used to predict or understand continental shelf‐sea carbonate system state and ocean health
(3111) Proposal to conserve the name Xenikoon australis (fossil Dinophyceae) with a conserved type
No full textA Tale of Two Shrimps—Speciation and Demography of Two Sympatric Shrimp Species From Hydrothermal Vents
No full textHydrothermal vents can serve as natural laboratories to study speciation processes due to their fragmented distribution, often with geographic barriers between habitats. Two sympatric species of Rimicaris shrimps occur at vents on the Izu-Bonin-Mariana volcanic arc: Rimicaris loihi also occurs near Hawai’i and R. cambonae is present on the Tonga Arc. These two species biogeographically co-occur and are genetically similar, raising questions about their speciation mechanisms, how they maintain distinct species, and whether interbreeding occurs. Here, we used barcoding and shotgun sequencing to test their genetic isolation and investigate their speciation process. We also evaluated population demography over 10 years to assess population densities and sex ratios at vents. Our results supported R. cambonae and R. loihi as two distinct species despite sympatry throughout part of their range. We also observed regional-scale genetic structure among R. loihi populations from the Izu-Bonin-Mariana volcanic arc, despite high dispersal potential. Finally, we found concomitant variations of shrimp densities and genetic diversity following fluctuations in geological and venting activities over a decade. A combination of geological instability, ocean currents dynamics and sea-level changes might drive temporary isolation among these local populations. We suggest that similar factors, with longer isolation periods, may also have promoted speciation between the two Rimicaris species, whereas distinct life-history traits could strengthen and maintain reproductive barriers. Overall, we found that the two species with large geographic distributions had significant patterns of genetic partitioning on a volcanic arc; this scenario contrasts with those observed previously at vents from mid-ocean ridges or back-arc basin systems
Circumpolar spread of avian influenza H5N1 to southern Indian Ocean islands
No full textSince 2020, the outbreak of high pathogenicity avian influenza (HPAI) H5N1 virus clade 2.3.4.4b has turned into the largest documented panzootic 1,3. Here, we describe its arrival into the Indian Ocean sub-Antarctic archipelagos of Crozet and Kerguelen, where we first detected the virus in October 2024 in dead southern elephant seals. While the panzootic is ongoing, it has already caused unprecedented mortalities of marine mammals and seabirds. We collected brain swabs from seal and seabird carcasses and obtained 25 novel HPAI H5N1 2.3.4.4b sequences. Using phylogeographic analyses, we show that there have been independent introductions of the virus to Crozet and Kerguelen islands, most likely from the distant South Georgia islands in the Southern Atlantic, and not from the more nearby coasts of South Africa. Our results point to a year-long gap in genomic surveillance in the sub-Antarctic region. Locally, our analyses show that the virus is transmitted between different species. Our serological analyses show that some southern elephant seal had mounted an anti-H5 antibody response. Through its circumpolar spread to the Indian Ocean, HPAI H5N1 2.3.4.4b moves closer to Australia, which remains free from infections with this strain, and represents a major threat to the sub-Antarctic wildlife
Conception et optimisation d’une enceinte étanche pour drone sous-marin
No full textDans les environnements marins, la protection des composants électroniques représente un enjeu crucial, omplexe et indispensable pour assurer la stabilité et la fiabilité des performances des véhicules sous-marins autonomes, en dépit de conditions extrêmes telles que les infiltrations d’eau et les fortes pressions. Cette étude porte sur la conception d’une enceinte de protection offrant un niveau élevé d’isolation et de robustesse mécanique. Une attention particulière a été portée à l’étude du système d’étanchéité, à l’agencement et à la fixation des composants internes, ainsi qu’à la gestion optimisée du câblage. Un système de gestion des câbles a été développé afin de minimiser l’enchevêtrement, améliorer la circulation interne, et simplifier les interventions de maintenance. Le choix des matériaux s’est orienté vers des solutions résistantes à la corrosion, compatibles avec une fabrication rapide et une installation efficace dans divers environnements marin
Characterizing an Incipient Fault System: Insights From the Morphometric Analysis of the North‐South Faults (Alboran Sea)
No full textInvestigating the dynamic evolution of active fault systems is fundamental for deciphering regional tectonics and assessing seismic risk, particularly in offshore regions where direct observation is challenging. Our ultra‐high‐resolution bathymetric study of the North‐South Faults (NSF) documents an incipient and dynamically evolving left‐lateral transtensional system, comprising 41 right‐stepping, highly segmented fault scarps and associated pockmarks. The NSF’s fault interactions and morphological scarp profiles analysis support a hybrid fault growth model, with coherent constant‐length growth predominating, and a sharp northwestern boundary reflecting an actively propagating shear zone. This kinematic interpretation is reinforced by en echelon patterns and focal mechanisms displaying strike‐slip and extensional components. The NSF appears to be the northward‐propagating tip of the larger Al‐Idrissi Fault, and its present‐day activity may be supported by fault‐aligned pockmarks. Empirical calculations show that faults can generate earthquakes up to Mw 6.5, and we propose the NSF as a plausible alternative source for the historical Mw 6.1, 1910 Adra earthquake, suggesting that a full system rupture could pose a greater seismic hazard to coastal populations than currently recognized. This research advances our understanding of early stage fault growth and provides valuable insights into the dynamics of evolving transtensional fault systems, applicable to other tectonically active offshore environments
Seasonal to long-term variability of natural and anthropogenic carbon concentrations and transports in the subpolar North Atlantic Ocean
No full textThe Atlantic Meridional Overturning Circulation (AMOC) is integral to the climate system, transporting heat and anthropogenic carbon across the North Atlantic (NA) from subtropical to subpolar latitudes. This physical mechanism promotes the uptake and sequestration of atmospheric CO2 through surface cooling as warm water advances northward and consequently sinks through deep winter convection. Using ship-based observations, ocean reanalyses, neural networks, and a back-calculation approach, we present a 30-year monthly time series of contemporary carbon (natural, Cnat and anthropogenic, Cant) concentrations and transports at the A25-OVIDE hydrographic section in the subpolar NA Ocean, and assess their variability from seasonal to long-term scales. We divided the section into essential layers, including the upper branch of the AMOC (uMOC) and the mixed layer (ML). Our findings indicate that the full-section-averaged Cnat concentration shows no significant trend over the 30-year period. In contrast, the full-section-averaged Cant concentration increased by more than one third over the 30-year period, attributed to anthropogenic influences and atmospheric CO2 increase. Seasonal and interannual variability is more pronounced in the uMOC and in the ML, where deep convection and biological activity impact their concentration. The seasonal deepening of the ML in winter contributes two thirds and one half of its ML concentration for Cnat and Cant, respectively, the rest being attributed to biology and solubility. The Cant and Cnat transports are predominantly determined by the variability of volume transport, except for the decadal trend in Cant transport which is primarily influenced by changes in Cant concentration. The variability in tracer transport is the largest in the uMOC, which exhibits a seasonal peak-to-peak amplitude of approximately 25 % of the annual mean tracer transport. These results offer new insights to refine model representations and improve our understanding of the subpolar NA carbon dynamics
Phylogeography of the widely distributed John Dory (Zeus faber, Actinopterygii: Zeiformes) reaffirms the prevalence of at least two deeply divergent clades
No full textThe John Dory Zeus faber is a commercially exploited demersal fish species with a known distribution ranging from the Northeast Atlantic to parts of the Indian and Pacific oceans. A previous genetic survey using cytochrome c oxidase subunit I (COI) DNA barcodes suggested the presence of two geographically segregated taxonomic units within Z. faber. We revisit this hypothesis by expanding the number and geographic coverage of DNA barcodes, addressing a major data gap along parts of the Atlantic coast of Africa and conducting a comprehensive phylogeographic analysis. Our findings consolidated the existence of two highly divergent mitochondrial clades, Clade A and Clade B (mean K2P distance: 7.4%), with the transition zone between them located along the Atlantic coast of Morocco. Clade A exhibited no phylogeographic structure, with haplotypes shared between Northeast Atlantic and Mediterranean populations. Conversely, four geographically structured subclades (mean K2P distance: 0.9%) were detected within Clade B, extending south and eastward from Morocco to Japan and New Zealand. Historical demographic events driving allopatric divergence, along with oceanographic and environmental factors, likely shaped the current geographic distribution of the two clades. These findings not only prompt the need to re‐evaluate the taxonomic status of Z. faber but also highlight the probable existence of multiple evolutionarily significant units (ESUs) that must be considered in the scope of stock assessment, fisheries management and conservation purposes