Characterisation Of Rhizaria in modern Oceans: from living cells to fossils

Can we simultaneously learn from past, present, and future oceans by studying plankton? For 521 million years, Rhizaria have abundantly and ubiquitously populated all oceans from the surface to the deep. They have biomineralised intricate skeletons by using silicon, thus impacting marine biogeochemical cycles. Upon death, their skeletons can become fossils and reflect ancient planktonic life. Yet, do fossils reflect all Rhizaria populations living in the water column? What is the fate of some large biomasses of contemporary Rhizaria that would have not been preserved as fossils? Ultimately, what is the interplay between live and fossilised forms? ChORhizO will provide a holistic and cross-disciplinary view of these questions, bridging disciplines from oceanography, biogeochemistry to micropaleontology. Rhizaria stocks, gravitational fluxes and fossil records will be quantified using a variety of innovative methods, from experimental to in situ approaches, from living cells to fossils. Oceanographic expeditions will be conducted in two contrasted oceanic basins (the Southern Ocean and Mediterranean Sea), where we observe imbalances between Rhizaria biomass and fossil composition. These basins will provide us with an opportunity to consider diverse water column alteration processes (i.e., taphonomy) that govern fossil record formation. New Vision moorings will be developed to investigate the detailed interplay between stocks and fluxes, ultimately fuelling fossil records. Over a period of two years, they will simultaneously quantify in situ both aspects at unprecedented scales: specimens spanning five orders of magnitude in size will be quantified along the entire water column. A precise understanding of how and which populations are reflected in fossil records will allow us to quantify the magnitude of modern biogeochemical cycles. Ultimately, ChORhizO will enhance our ability to reconstruct past ocean conditions as well as predict future fossil assemblages.