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The Silicon Cycle: The Forgotten Silicified

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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 : https://www-iuem.univ-brest.fr/cycle-du-silicium-dans-locean/

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

New Recognition for Major Players in the Ocean’s Silicon Cycle

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Functional ecology

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Understanding the role and functions of organisms in their living environment is a major objective set by the DISCOVERY team. To simplify the representation of biodiversity and its role in the functioning of ecosystems, a functional approach to biodiversity is used by looking for groups of species, characterised by common biological traits (trophic mode, mobility, sediment reworking, bioirrigation, etc.) that have homologous effects on key ecological functions (e.g. food webs, primary production, photosynthesis, biogeochemical fluxes, bioturbation, etc.). Particular attention will be paid to the variability of biological traits (functional redundancy) in response to biotic and abiotic interactions, and to the study of interactions between functional groups (facilitation, complementarity, inhibition, competition) in order to appreciate the complexity of communities. This information will enable us to conceptualise, develop and parameterise models of community structuring and ecosystem functioning.

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Role of complex trophic interactions in biogeochemical cycles

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Noctiluca scintillans variashttp://planktonnet.awi.de (provided under a Creative Commons Attribution 3.0 License)

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.

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Carbon fate in the deep ocean

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Source: https://www.pexels.com/

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: https://jetzon.org/) coordinating programmes on the mesopelagic zone.

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The ocean dynamics is structured on scales ranging from a thousand kilometers, a few meters, through the tens / hundreds of kilometers.

Identification, study and development of molecules and ingredients of marine origin for health and biotechnology

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Marine environments are home to a wide variety of organisms whose physiology has adapted to the biotic and abiotic constraints of their environment, adapting their cellular functioning and producing original primary and/or secondary metabolites. These cellular mechanisms and these compounds, whether they are involved in vital processes or in inter-organism interactions, represent a reservoir of potentially valuable molecules in human, animal and plant health, in cosmetics, in agri-food and more generally in biotechnology. The aim is to take advantage of the knowledge acquired on marine biodiversity, chemical ecology and the cellular mechanisms of marine organisms, to isolate, characterise and develop mechanisms and bioactive substances that can be used to combat certain diseases, families of compounds that are beneficial to human and animal health, or of interest in biotechnology. It is also a question of imagining tomorrow’s biotechnological developments in innovative fields such as biomimetic approaches for the development of biocompatible materials, the emergence of natural products from sustainable approaches, or the fight against biofouling. The identification of fundamental, ancestral and original mechanisms present in marine organisms represents a source of inspiration for mimicking these processes in human health, in the fight against certain metabolic pathologies or cellular disorders, thus accelerating our interface perspectives towards clinical research.

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An major research theme at LEMAR on which the unit displays complementary skills and unique expertise in the West

Copyright : Laboratoire LEMAR- 2018

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