French Research Institute for Exploitation of the Sea
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Mg/Ca from Mussel Shells Rather than Δ18o as a Promising Temperature Proxy for Hydrothermal Vent Ecosystems
No full textMinor and trace metal fluctuations in biogenic carbonates have been demonstrated to be important potential environmental tracers in coastal areas, but remained poorly studied in deep-sea environments. For the first time, this study assesses the use of Mg/Ca signal as a thermometer proxy in hydrothermal vent ecosystems together with the analysis of oxygen stable isotope composition. Bathymodiolus azoricus and B. thermophilus mussels were collected at three hydrothermal vent fields from the mid-Atlantic ridge (Rainbow, Menez Gwen) and the East Pacific Rise (EPR 9°50N), presenting contrasted temperature and chemical habitat conditions. The variation of Mg/Ca was analysed via LA-ICP-MS and is revealed suitable to reconstruct temperature variations in these ecosystems, presumably due to stable Mg compositions of the seawater surrounding hydrothermal systems. Temperature anomalies inferred from Mg/Ca ratios can be good tracers of fluid pulses. Important fluid emissions appear however to generate major growth cessation in shell mineralization Temperatures inferred from IRMS δ18O analyses systematically underestimated the measured values in the environment. The isotopic disequilibrium is likely due to pH fluctuations in the mussel habitat, in the vicinity of vent fluid discharges, and/or interactions with the symbiotic chemosynthetic bacteria. Those results will first benefit to the ecological study of deep-sea mussels, but also provide a promising contribution for the study of the environmental dynamic in hydrothermal systems at short (daily) to long-term (pluri-annual) scales, recorded in the calcite material of bivalves
25th Argo Data Management Team meeting, Trieste, 21-25 October 2024
No full textThe ADMT-25 - 25th Argo data management team meting took place in Trieste on 21-25 October 2024.
Winter dynamics of phytoplankton and micronutrients in the Southern Ocean
No full textCombined observations of phytoplankton abundance, community structure, and trace metals are limited but crucial for understanding Southern Ocean biogeochemistry. While summer studies exist, winter research is scarce. This study provides a fundamental first overview of phytoplankton-micronutrient (i.e. trace metals) dynamics during early winter in the Indian sector of the Southern Ocean. Depth-resolved measurements were taken for chlorophyll-a, phytoplankton composition, and micronutrients iron (Fe), manganese (Mn), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), and cadmium (Cd). Phytoplankton abundance (0.27 - 0.08 µg L-1 chlorophyll-a), and presumably, metal uptake were low in winter. In the Subtropical Zone, cyanobacteria and haptophytes dominated, driven by the interplay of higher temperatures, limiting macronutrients, and trace metals such as Fe and Zn, while also influencing Co and Mn dynamics through biological uptake. In the Subantarctic and Polar Frontal Zones prasinophytes dominated, cyanobacteria were linked to Co uptake, while Mn and Zn deficiency and silicic acid limitation constrained diatoms. In contrast, flagellate groups, such as the dominant prasinophytes, may have compensated through substitution. In the Antarctic Zone, Fe and Mn were the primary limiting nutrients for the dominating diatoms, as silicic acid was no longer limiting. In turn, diatoms strongly influenced Zn particulates through biological uptake, while Phaeocystis and coccolithophores appear to have contributed more to Cd uptake. This winter perspective on phytoplankton-micronutrient relationships shows that phytoplankton continue to influence particulate trace metal distribution despite their low productivity and that there are strong phytoplankton group-specific associations with various essential metals, rather than iron alone, that vary latitudinally
En‐échelon Rifting and Origin of the Volcanism in the Comoros
No full textTwo volcanic provinces have been recently discovered during the SISMAORE oceanographic cruise in the Comoros archipelago in the North Mozambique Channel between Madagascar and East Africa: N’Droundé, along the North‐eastern insular slopes of Grande Comores Island and Mwezi, in the abyssal plain, north‐east of Mayotte and Anjouan islands. By combining bathymetry and backscatter data, high‐resolution seismic reflection and sub‐bottom profiles, we have identified and mapped various tectonic (faults, forced folds) and volcanic structures (lava flows, edifices, sills, dykes) at several spatial scales on the seabed and in cross‐section within the sedimentary cover. We have characterized the volcano‐tectonic structures (geometry, segmentation, and kinematics) to better understand the link (geometry, chronology) between tectonic and volcanic processes. We show that volcanic and tectonic features are controlled by tectonic processes and vice‐versa. Ridges, volcanic cones and lava flows are set up along fissures and dikes during main rifting events to accommodate a N40°E regional extension within an E‐W right lateral shear transfer zone. The volcano tectonic features are Plio‐Pleistocene. This transfer zone lies between the offshore branch of the East African rift system and Malagasy grabens and may have formed when the East African rifts propagated offshore. We evidence a major rifting episode in the last Ma. The estimated volume and flux of extruded lavas show that the volcanism of the Comoros could be related to shallow tectonic processes
Research for anticipating and facilitating change in fisheries management
No full textIn this article, I am considering the changes that occurred in fisheries science during the last three decades from a personal scientific point of view and as a woman in science. The contribution and visibility of women in this field has increased, though further progress is possible
Origin and Pathways of Source Water Masses in an Upwelling Bay: The Case of Paracas Bay Off Southern Peru
No full textThis study aims to characterize the properties of source water masses emerging in the coastal bay of Paracas, an anthropized bay embedded within the peruvian upwelling system. A Lagrangian modeling approach is used based on hydrodynamical conditions from a previous modelling study. Lagrangian floats representing water parcels were launched in the bay and advected backward in time for 15 days by the simulated currents. Hydrodynamic conditions represented synoptic, seasonally modulated, wind-driven currents, influenced or not by the passage of a downwelling poleward propagating coastal trapped wave, mimicking El Niño conditions. The bay source waters originated mainly from the shelf and slope north of the bay, coherently with the poleward subsurface circulation, with no connection to regions south of the bay. As expected from seasonal changes in stratification, the average depth, depth and temperature ranges of the source waters were larger in winter than in summer. During the propagation of the downwelling coastal waves, the poleward flow over the inner shelf north of the bay intensified, filling the bay with warmer and shallower source waters. Implications on the oxygenation of the bay are discussed.This study detailed insight into the dynamics of the source waters and the potential influence of seasonal and interannual variability, such as El Niño events, on the circulation and properties of water masses in the bay
Working Group on Fisheries Benthic Impact and Trade-offs (WGFBIT; outputs from 2024 meeting)
No full textThe Working Group on Fisheries Benthic Impact and Trade-offs (WGFBIT) develops methods and assessments to evaluate fisheries’ benthic impact at a regional scale while considering trade-offs between fisheries and seabed health. This report summarizes progress on a European-wide assessment of bottom trawl impacts, presenting the first quantitative evaluation across the Baltic, Atlantic, Mediterranean, and Black Seas. Using indicators of seabed status—RBStot (biomass rel-ative to fauna carrying capacity) and RBSsen (biomass of the 10% most sensitive fauna relative to carrying capacity)—significant regional and habitat differences in bottom trawling impacts were identified. Methods to differentiate between good and degraded states were further re-fined, including probability-based approaches for seabed condition assessment. A roadmap was established to implement a Core Fishing Grounds Analysis (CFGA) across all EU marine regions within the 2024–2027 cycle. CFGs aim to balance sustainable fishing and en-vironmental goals by protecting high-value fishing areas. Discussions addressed current limita-tions of CFGA and guidelines for defining scenarios in trade-off analyses. A preliminary exercise using Atlantic and Mediterranean data explored the effects of varying RBS values on surface area, landing value, fishing effort, and weight. Assuming RBS = 0.8 as the threshold for a "good" condition, the study assessed reductions in exploited areas and fishing efforts needed to meet EU marine targets (D6C5 Adverse Effects on Habitats). The BFIAT (Bottom Fishing Impact Assessment Tool) model was advanced to predict trawling-induced habitat changes and their impact on biological processes like bioturbation. Case studies in the Celtic Sea, Greek waters, Baltic Sea, and Kattegat utilized datasets linking macrofauna traits to biogeochemical processes under different fishing and hydrodynamic regimes. Outputs from BFIAT are integrated with models like OMEXDIA to evaluate sediment carbon processing and with 3D models (NEMO/SPM-IOW, NEMO-ERSEM) to analyze carbon dynamics and dep-osition. Future work will examine the impacts of fauna reduction, sediment mixing, and carbon decay on ecosystem processe
Working Group on Shipping Impacts in the Marine Environment (WGSHIP; outputs from 2024 meeting)
No full text
Convergent iridescence and divergent chemical signals in sympatric sister-species of Amazonian butterflies
No full textThe evolution of traits in closely-related species living in sympatry strongly depends on both shared selective pressures and reproductive interference. In closely-related Morpho butterfly species living in the understory of the neo-tropical rainforest, the blue iridescent coloration of the wings is likely involved in predation evasion, as well as in mate recognition and courtship. We used spectrophotometry, behavioral experiments, visual modeling, and chemical analyses to characterize the evolution of visual and chemical traits in two closely-related species, Morpho helenor and Morpho achilles. We specifically compared trait variation between samples from allopatric and sympatric populations of M. helenor to test the effect of ecological interactions with M. achilles on trait evolution. We quantified the differences in wing iridescence and tested for variations in the sexual preference for this trait. We found a strong similarity in iridescence between M. helenor and M. achilles in sympatry, while the iridescence of M. helenor diverged in allopatry, suggesting that predation favors local resemblance. Although intraspecific behavioral experiments showed that iridescent signals could be used as visual cues during intraspecific mate choice, the strong resemblance of the iridescent signals between species may impair these species' visual recognition. In contrast, the divergent chemical bouquets detected between species suggest that the visual similarity of sympatric Morpho species may have favored the divergence of alternative traits involved in species recognition, such as chemical cues