COccolithophore CarbOnate PROduction: from the PETM to future oceans

Objective

Carbon dioxide (CO2) from human activities is the main cause of today’s global warming. To tackle this challenge, we need to understand how Earth naturally stores carbon-especially in the ocean, the planet’s largest carbon sink. Coccolithophores, microscopic marine algae, are key players in this process. Through photosynthesis, they absorb atmospheric CO2 and convert it into organic carbon, while simultaneously forming protective tests (coccoliths) made of calcium carbonate, thereby fixing inorganic carbon. When they die, their carbonate plates sink to the seafloor, accumulating over time (a process known as carbonate flux) and becoming part of the fossil record. Today, coccolithophores dominate marine carbonate fluxes (50–90%), but the carbonate contribution of their fossil counterparts, calcareous nannofossils (CN), in past oceans is largely unknown. COCO-PRO addresses this gap by calculating, for the first time, how much carbonate was produced and exported to the seafloor by individual CN species during the Paleocene–Eocene Thermal Maximum (PETM, ~56 million years ago), a past global warming event considered the closest analogue to today’s climate change. The project combines precisely dated marine reference sections, quantitative species counts, morphometric and geometric measurements to calculate species-specific carbonate flux with unprecedented taxonomic and temporal resolution. By integrating approaches from paleoclimatology, micropaleontology, biogeochemistry, marine biology and geometry, COCO-PRO will reveal how CN species responded to past warming and ocean acidification, while producing the first-ever species-specific CN carbonate flux data for a hyperthermal event. These results will improve climate models, guide mitigation strategies, and directly support EU priorities and Sustainable Development Goals (SDGs 13, 14, 12, 4 and 5), thereby enhancing Europe's capacity for climate action, ocean sustainability, gender equality, and knowledge transfer.