CE01 - Terre fluide et solide

Role of Rhizaria in biogeochemical Cycles in the epi-and mesopelagic ocean – RhiCycle

The elusive role of Rhizaria in oceanic biogeochemical cycles

Considering their broad size spectra and extended range of vertical habitats, substantial contribution to the marine carbon pool, what is the significance of rhizarians in biogeochemical cycles, in particular carbon and silica cycling?

Understand the role and quantitative contribution of Rhizaria in contemporary biogeochemical cycles, extending from the epipelagic to the mesopelagic ocean

1) Objective 1 aims to assess the elemental composition and sinking rates of a broad taxonomic and size range of silicified rhizarians<br /><br />2) Objective 2 aims to evaluate the contribution of rhizarians to POC and bSiO2 fluxes, from the epipelagic to the mesopelagic zone using sediment traps<br /><br />3) Objective 3 aims to provide quantitative information about the vertical distributions of rhizarian populations using in situ and automated imaging systems. Specifically, it will allow comparison of vertical fluxes with abundances in order to derive rhizarian’s (i) turnover times, (ii) growth rates and (iii) carbon demand. These biotic variables will be used to infer the impact of flux-feeding phaeodarians impact on carbon flux attenuation in the ocean water column.<br /><br />The full characterization and quantification of the impact of rhizarians on carbon and silica cycling has not yet been attempted in any part of the ocean. Consequently, given their new-found importance in marine communities and ocean processes, this project will significantly expand our knowledge of rhizarian ecology as well as understanding of biogeochemical processes, in particular in the mesopelagic ocean. This may radically change our perception of the role and significance of these unicellular organisms in structuring marine ecosystems and biogeochemical cycles. RhiCycle will deliver useful and comprehensive information not only for biogeochemists and/or modelers willing to include rhizarians in their biogeochemical budgets and/or models, but also for plankton ecologists.

-Imagery in situ (underwater vision profiler 5 and 6)
-Elemental composition (carbon and silicon) of marine rhizarians
-Vertical flux quantification
-Geochemical quantification of total fluxes (carbon and biogenic silica)

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Planktonic organisms play crucial roles in biogeochemical cycles that regulate Earth’s climate. Within planktonic communities, Rhizaria are diverse protists that build complex mineralized skeletons, for some, of biogenic silica. In recent years, they have begun to emerge as important organisms structuring planktonic communities and modulating biogeochemical processes linked to the silica and carbon cycles. Yet, considering their broad size spectra and extended range of vertical habitats, they still lack a full characterization and quantification of their impacts (i.e., export and flux attenuation) on these processes. To this end, the RhiCycle project will evaluate the role and quantitative contribution of Rhizaria in marine biogeochemical cycles, in particular the biological carbon pump and marine silica cycle, extending from the epipelagic to the mesopelagic ocean. Built around a multidisciplinary team of internationally recognized experts, an original combination of tools and expertise encompassing marine biogeochemistry, quantitative in situ imaging, sediment trap fluxes and molecular characterizations of diversity will be used. Designed to complement regional field studies and oceanographic cruises in a variety of ecosystems, laboratory experiments will generate information needed to interpret large-scale studies in different major oceanic basins (Northeastern Pacific, North Atlantic). Ultimately, since the full characterization and quantification of the impact of rhizarians on these processes has not yet been done in any part of the ocean, and given their new-found importance in marine biota, this project will significantly improve upon our knowledge of rhizarian ecology as well as expand understanding of key biogeochemical processes affecting the mesopelagic ocean.

Project coordinator

Monsieur Tristan Biard (Université du Littoral Côte d'Opale (ULCO), Laboratoire d'Océanologie et de Géosciences (LOG))

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

FSU-PEB Florida State University / Plankton Ecology and Biogeochemistry
SIO-IOD Scripps Institution of Oceanography / Integrative Oceanography Division
CNRS-LOV Laboratoire d'Océanographie de Villefranche-sur-mer (LOV)
CNRS-LEMAR CNRS, Laboratoire des sciences de l'Environnement Marin (CNRS-LEMAR)
ULCO-LOG Université du Littoral Côte d'Opale (ULCO), Laboratoire d'Océanologie et de Géosciences (LOG)

Help of the ANR 256,176 euros
Beginning and duration of the scientific project: December 2019 - 48 Months

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