Assessing the Role of cheMolithoautotrOphy on caRbon fluxes in the mesopelagIC realm. – ARMORIC

The biological carbon pump (BCP) regulates the Earth’s climate by sequestrating photosynthetically fixed CO2 into the dark ocean. The BCP occurs in the form of organic carbon particles (POC) from planktic origins sinking below the surface. POC flux attenuates with depth through remineralisation by heterotrophic organisms. However, the variability of POC flux attenuation remains unexplained. Recent work showed that prokaryotes (Archaea and Bacteria) converting dissolved CO2 into POC (dark CO2 fixers) exist on sinking particles in the dark ocean. Yet, this potentially important new source of C to the dark ocean is not considered in POC flux attenuation. Combining innovative sampling strategy and measurements techniques, ARMORIC will generate unprecedented data on prokaryotic dark CO2 fixation rates and diversity associated to sinking POC. Accounting for dark CO2 fixation on POC may revolutionise conventional views on the apparent quantity of sinking POC being respired in the dark ocean.