Campaign Summary Report - Mission Microbiomes from Buenos Aires (2021-12-04) to Ushuaia (2021-12-27) on board AtlantECO flagship SV Tara

The Tara MM Gayoso experiment: A holistic study of coccolithophore bloom dynamics. Every spring, the Patagonian shelf and shelf-break experience massive phytoplankton blooms. While diatoms and dinoflagellates dominate at the beginning, gigantic patches of high reflectance waters associated with coccolithophores are detected towards December. These develop in long (100-1000 km) south-to-north streaks along the shelf-break for several weeks, on the track of the strong, northward-flowing Malvinas Current. Whether the bloom is only advected or also benefits from upwellings and therefore fertilization processes triggered by the current along the shelf break is currently not known. Our specific questions are: (a) What are the ecosystem dynamics of a coccolithophore bloom and demise? (b) What are the contributions of different mortality agents (viruses, bacteria, allelopathy, grazers) in the bloom's demise and its metabolic footprint? (c) What is the role of infochemicals as mediators (notably through vesicles) of microbial interactions? (d) What are the large-scale biogeochemical consequences of microbial interactions? (e) Which type of microorganisms, viruses, and bacteria are emitted from coccolithophore blooms? (f) How does the Patagonian bloom relate to global coccolithophore biology? To address these questions, we deployed a unique sampling plan in a joint effort with a local Argentinian consortium. In November 2021, the mythical sailing boat ‘Motovelero Bernardo Houssay’ applied the AtlantEco multi-omics protocol to assess the early stages of the bloom from Ushuaia to Buenos Aires. The ‘Houssay’ met ‘Tara’ in Buenos Aires, and Tara performed in December 2021 a Lagrangian drift on a coccolithophore patch, guided by satellite data and SVP drifters, and deploying to our knowledge the most advanced eco-systemic protocols ever applied to a natural plankton bloom. This included, beyond the meta-omics (meta-B/G/T) samples, new protocols to assess the extracellular vesicles, single cell transcriptomics, the meta-proteome and meta-metabolome, the surface micro layer, a suite of specific methods targeting lipid- and gene-based molecular biomarkers of coccolithophores and their viruses, together with in-situ continuous measurements using optical sensors