Links between biogeochemical cycles of metals and living organisms


Improving our knowledge of the metal cycle in contrasting environments of the world ocean is absolutely necessary for a better understanding of the oceanic biogeochemical cycles of major elements (C, Si, N, S) and the biological carbon pump. LEMAR is internationally recognised in this field, in particular through our strong involvement in the GEOTRACES programme. We combine observations, field or laboratory experiments and modelling. Our originality lies in the combined study of the dissolved and particulate phases, as well as their speciation (redox and organic), in order to better understand the interactions between these two reservoirs, which are fundamental in the metal cycle and yet are still little studied. Our expertise also includes the study of interactions between the metal cycle and plankton, by linking metal speciation to the bioavailability of micronutrients for marine plankton (phytoplankton and bacteria). The integration of omics tools (functional genomics, transcriptomics, etc.) into this theme is currently essential to further investigate the link between biogeochemical cycles of metals and interactions with living organisms. These explorations will continue to be carried out, both during oceanographic missions and in laboratory studies, notably thanks to our numerous international collaborations and our involvement in the future international programme BioGeoSCAPES (‘Ocean metabolism and nutrient cycles on a changing planet’). The strong international momentum of the GEOTRACES programme and the forthcoming BioGeoSCAPES programme now allows us to build and meet the challenge of integrated microbial biogeochemistry projects that require international coordination with a multidisciplinary approach.

The Silicon Cycle: The Forgotten Silicified


Le cycle du silicium est une thématique historique du LEMAR qui possède une forte visibilité internationale grâce à notre implication dans les programmes et consortium internationaux comme BioGeoSCAPES, IMBER, IODP, GEOTRACES, OPALEO, PAGES et SILICAMICS. Nous avons développé une approche transdisciplinaire, incluant la chimie, la biogéochimie, la paléo-océanographie, la biochimie, la physiologie, la biologie et, nouvellement, la génomique. Nous utilisons par ailleurs différents outils expérimentaux et de modélisation et des approches multi-échelles, depuis des expériences au laboratoire qui permettent de mieux comprendre les processus influençant le cycle du Si jusqu’à de grandes campagnes internationales d’observation du milieu naturel. Le «Si-group» a initié en 2015 le cycle de conférences internationales SILICAMICS autour du rôle des organismes silicifiants dans le fonctionnement des écosystèmes marins et dans les cycles biogéochimiques océaniques. SILICAMICS s’est poursuivie au Canada en 2018, et une 3 ème édition est en préparation en Chine (2021). Suite à ces conférences, l’article de Nature Geoscience (Tréguer et al., 2018) combine les compétences d’experts en physique, biogéochimie, génomique et modélisation pour faire le point sur l’efficacité d’export des diatomées ; l’issue spéciale de Frontiers in Marine Science (Moriceau et al. 2019) rassemble 12 articles couvrant les thèmes de SILICAMICS et deux ANRs (BIOPSIS et RADICAL) ont vu le jour, mettant en évidence la nécessité de réévaluer le rôle des silicifiés oubliés dans le cycle du Si (voir AR2.2 CHIBIDO). Ces épisodes ont de plus été moteurs dans la création d’un consortium puis d’une école internationale et cours en ligne (Silica School) réunissant 31 instituts de recherche de 12 pays. De nombreux chercheurs invités régulièrement au LEMAR garantissent le dynamisme et la visibilité de cette thématique du LEMAR au niveau international.


Pour en savoir plus :

Le cycle du silicium dans l’océan moderne :

Research topic dans Frontiers in Marine Sciences: Biogeochemistry and Genomics of Silicification and Silicifiers

Role of complex trophic interactions in biogeochemical cycles


In the ocean, trophic interactions between individuals are still mainly represented in a predator-prey pattern. However, meta-analyses of taxonomic co-occurrences, made possible by advances in molecular biology, suggest that many planktonic organisms are involved in complex interactions ranging from facultative predation to symbiosis to mutualism. While these relationships appear to be the rule rather than the exception in the ocean, research efforts are focused on a few emblematic examples. In CHIBIDO, we are trying to identify new interactions and are particularly interested in mixotrophic organisms (both phototrophic and phagotrophic), the trophic mode of the majority of dinoflagellates, and in diazotrophs that often live in symbiosis with other organisms. To better understand the role of trophic interactions on biogeochemical cycles (especially nitrogen and carbon), it is necessary to couple tools.

The team is internationally recognised for its expertise in the use of 13 C and 15 N stable isotopes to quantify oceanic fluxes. In recent years, it has coupled this approach with new tools (e.g. nanoSIMS or flow cytometry sorting) that make it possible to visualise and quantify fluxes between the environment and organisms and/or between organisms.

Carbon fate in the deep ocean


The biological carbon pump can be broken down into three stages: the formation of biogenic carbon at the surface (production), the transfer below the mixed layer (export) and the attenuation of the flux in the mesopelagic zone (200-2000 m), towards long-term storage (> 1000 years) in the deep ocean and sediments. For operational reasons, the years 1980-2000 were strongly focused on the first two components of the biological pump (international JGOFS programme). The depth of carbon flux attenuation with depth, which imposes strong constraints on the time scales of carbon storage in the deep ocean, is constrained by ocean dynamics (turbulence, small scales, etc.), dissolution processes, biological activity (heterotrophic activity, respiration) and particle behaviour (sedimentation, aggregation/desaggregation). The evolution of observation means (autonomous platforms, high frequency measurements, acoustics, imaging, molecular biology, etc.), as well as progress in modelling (computer power, taking complexity into account, Artificial Intelligence), now make it possible to tackle this question head-on. LEMAR is fully involved in this new dynamic and relies on its expertise in the description of the fate of dissolved organic matter, the silicon, iron and carbon cycles, the role of zooplankton, remineralisation processes, particle dynamics, the study of the small scale in the mesopelagic zone (see AR2. 1 CHIBIDO), modelling (in connection with the ITM Atlantic teams developing approaches in Artificial Intelligence), microbiology or ecology to get involved and carry out international projects on this topic. In addition, the laboratory actively participated in the creation of the international consortium JETZON (Joint Exploration of the Twilight Zone Ocean Network: coordinating programmes on the mesopelagic zone.