Ugo Guignard, stagiaire Master 2 LCE collaborant avec le MIO, donnera un séminaire en salle de réunion du LCE à St Charles, le mardi 30 juin 2026 à 14h00 sur le thème : Volatile Organic Compound Emissions and their Relationship with Phytoplankton Communities.

Lien Visioconférence

Résumé

Species-resolved volatile organic compounds (VOC) emission inventories of marine phytoplankton remain incomplete, limiting the accuracy of marine biogenic gas flux parametrisations in atmospheric and climate models. In particular, the relative con-tributions of specific taxa to the budgets of key aerosol precursors – dimethylsulfide (DMS), methanethiol (MeSH) and isoprene – are poorly constrained because field measurements integrate signals from mixed communities. To address these gaps, this thesis combines two complementary approaches: the VACOA ship campaign aboard the Marion Dufresne II across the Southern and Indian Oceans (January–February 2026), providing large-scale in situ observations of VOCs, aerosol composition and phytoplankton communities across six oceanographic periods; and the SARNEIO lab-oratory incubation experiment, comparing VOC emissions from two ecologically con-trasting phytoplankton species – Thalassiosira pseudonana (diatom) and Phaeocystis globosa (haptophyte) under identical controlled conditions.
During VACOA, DMS concentration peaked at frontal zones as expected, but three findings departed from predictions. The campaign-wide DMS–sulfate corre-lation was negligible (ρ = −0.085), likely attributed to the multi-day atmospheric oxidation lifetime of DMS and to the variable marine boundary layer fraction, which reached zero percent boundary-layer-dominated days during the biologically produc-tive Polar Front period. MeSH concentration showed a more coherent positive relationship with sulfate (ρ = +0.224), consistent with its faster oxidation kinetics. DMS and MeSH concentrations were strongly negatively correlated in the most productive periods (ρ = −0.70 and −0.82), suggesting competition between the DMSP lyase and demethylation pathways. Isoprene persisted in oligotrophic subtropical regions despite minimal phytoplankton biomass, showed no consistent diurnal cycle and was decoupled from nanophytoplankton abundance, likely pointing to a significant abiotic photochemical source at the sea surface microlayer.
In SARNEIO, preliminary PTR-ToF-MS measurements revealed contrasting emission dynamics across all three compounds. P. globosa showed continuously el-evated DMS and MeSH concentration declining with cell senescence, and near-zero isoprene concentrations, consistent with a high-DMSP haptophyte channelling antiox-idant protection through the sulfur pathway. T. pseudonana displayed a delayed DMS concentration increase coupled to the bloom peak, no corresponding MeSH concentra-tion increase — suggesting lyase dominance over demethylation during active growth and a variable isoprene signal whose quantification awaits resolution of an elevated blank. These species contrastscontrast impliesy that haptophyte- and diatom-dominated blooms contribute to atmospheric VOCs with different fingerprints and at different phases of the growth cycle.

Dr. Irene Nadal-Arizo, jeune chercheuse à l’Université de Málaga, donnera un séminaire à l’Amphithéâtre OCEANOMED, Bâtiment Méditerranée, Campus de Luminy, le jeudi 25 juin 2026 à 11h00 (30 min de présentation & 15 min de questions) sur le thème : Unravelling the physics behind marine life: applied modelling studies in the Mediterranean Sea and Eastern Atlantic Ocean.

Courte biographie 

Après avoir obtenu son diplôme en sciences marines, le Dr Irene Nadal-Arizo a soutenu une thèse de doctorat en océanographie physique à l’université de Málaga, où elle a développé un intérêt pour les interactions entre la physique océanique et les écosystèmes marins. Ses travaux de recherche portaient sur l’utilisation de modèles numériques pour étudier le transport, la dispersion et la connectivité en mer, en particulier dans les zones côtières, en appliquant des approches lagrangiennes à différents sujets d’intérêt, notamment les stocks halieutiques, les algues envahissantes et les déchets marins. Plus récemment, elle a étudié comment les changements climatiques liés à la température, aux remontées d’eau et à la disponibilité alimentaire peuvent affecter la répartition, la productivité et la dynamique des petites espèces pélagiques dans le système de remontée d’eau au large de l’Afrique du Nord-Ouest. Elle est actuellement en visite au MIO pendant deux semaines afin de rédiger une demande de bourse postdoctorale MSCA.

Résumé

Hydrodynamic features play a crucial role in shaping the dispersal, connectivity, and population dynamics of marine species. Here we explore how physics-to-biology modelling frameworks can help elucidate the mechanisms by which hydrodynamic processes govern biological outcomes in two environmentally dynamic regions. First, in the Mediterranean Sea, a Lagrangian particle tracking algorithm coupled to a high-resolution hydrodynamic model is used to map dispersal pathways in the Alboran and Adriatic Seas, with applications including fish larvae and invasive macroalgae. Shifting to the Eastern Atlantic, an end-to-end modelling framework coupling ocean circulation, lower-trophic ecosystem and individual-based models is applied to two small pelagic species in the Canary Current Upwelling System, to identify mechanisms by which large-scale climate variability impacts their spatiotemporal dynamics, and to generate future projections of abundance and biomass distribution. Finally, a collaborative project with CNRS-MIO exploring new physics-to-biology frameworks for other commercially important marine species is presented.

Pedro Junger, jeune chercheur à l’Institut de Biologie de l’École Normale Supérieure de Paris, donnera un séminaire à l’Amphithéâtre OCEANOMED, Bâtiment Méditerranée, Campus de Luminy, le mardi 16 juin 2026 à 11h00 sur le thème : Linking genomics and remote sensing to diagnose phytoplankton iron stress in the global ocean.

Résumé

Marine ecosystems rely almost entirely on primary production provided by phytoplankton, which globally perform 50% of the photosynthesis on our planet, fixing atmospheric carbon dioxide and driving the biological carbon pump, a key process in climate regulation. Their ability to capture carbon, however, depends on the availability of scarce nutrients like iron. Climate change and human activities are shifting the oceanic distribution and bioavailability of iron, yet the responses of different phytoplankton groups to these changes remain poorly understood.

In this talk, I will describe how we combined omics data and satellite observations to map phytoplankton iron nutritional status at the global scale. We analyzed the abundance and expression of iron-responsive genes in metagenomes (n=2,155) and metatranscriptomes (n=1,466) from 655 stations across three global ocean expeditions.

Our approach exploits a well-known physiological response: under iron limitation, phytoplankton swap iron-containing proteins in the photosynthetic electron transport chain (ferredoxin, cytochrome c6) for iron-free alternatives (flavodoxin, plastocyanin). The ratio between these protein pairs serves as a proxy for iron stress. These genomic proxies correlated strongly with satellite-derived estimates of phytoplankton physiological status and modeled iron concentrations. Using a Random Forest model trained on satellite products, biogeochemical model outputs, and nutrient data, we predicted global distributions of iron stress that accurately captured well-known iron-limited regions, including the Southern Ocean, equatorial Pacific, and subarctic Pacific. Validation against independent bottle bioassays confirmed metatranscriptomics as particularly well-suited for diagnosing iron stress in situ. This work provides a scalable framework for linking genomics and remote sensing to monitor global phytoplankton iron stress.

Alexandre Che-Pelicier du laboratoire Molecular Surveillance, Environmental Science Department  du Cawthron Institute, Auckland University of Technology, Earth Sciences New Zealand, donnera un séminaire à l’Amphithéâtre OCEANOMED, Bâtiment Méditerranée, Campus de Luminy, le mardi 16 juin 2026 à 13h00 sur le thème : Les isotopes stables et l’ADN environnemental peuvent-ils aider à comprendre la mystérieuse vie marine des anguilles de Nouvelle-Zélande ?

Lien Zoom

Résumé

Les zones de reproduction et les voies de dispersion larvaire de deux espèces d’anguilles de Nouvelle-Zélande restent inconnues, rendant leur cycle de vie encore partiellement incompris. Bien que la pose de balises ou de tags soit utilisée pour suivre les déplacements de certains animaux marins, ces méthodes sont difficiles à appliquer aux anguilles adultes et à leurs larves (leptocéphales). Cette présentation portera sur l’utilisation de marqueurs biochimiques et moléculaires afin de reconstruire les routes de migration de ces deux espèces entre l’océan Pacifique tropical et les rivières tempérées de Nouvelle Zélande.

Mots clés

Migrations marines, Leptocephales, Anguilles, Isotopes stables, Isoscapes, ADN environmental.