HOPE uses an ambitious approach at the interface between microbial oceanography, geochemistry and autonomous sensor technology. The general approach combines both lab (WP1) and in situ (WP2, WP3) approaches, studying processes occurring at different spatiotemporal scales. At this stage of the project (2 years), the 3 WPs have been started.
-In WP1, we designed and realized a specific prototype device able to study the dynamics of diazotroph-derived particles in the lab, i.e. the SOCRATE experimental column (Simulated OCean wateR column with AutomaTEd sampling). Briefly, SOCRATE is an illuminated and temperature-controlled experimental 6 m-high water column fitted with a wave simulator in surface, and three sediment traps at the base to collect particles at desired time intervals. Sinking particles can be automatically and simultaneously sampled at desired time intervals without perturbation at every meter along the column, and their sinking velocity is measured by cameras fitted in the column. This column makes it possible to acquire metrics that are not accessible in the natural ocean (size, shape descriptors of particles, aggregation rates, sinking velocities, remineralization rates of specific diazotrophs, etc.) that are essential to be integrated in the marine components of the climate models used by the IPCC.
-In WP2, we performed 3 oceanographic expeditions (32 days at sea in 2024) onboard the Research Vessel ANTEA in the subtropical South Pacific Ocean. We used a combined strategy aiming at deploying 1000 m-long drifting mooring lines fitted with sinking particle traps in the deep ocean and studying carbon trophic flows in surface, to shed light on the complex carbon export pathways to the deep ocean.
-In WP3, we deployed in the South Pacific Ocean a smart profiling buoy (HOPE'ORTUNITY) equipped with high-tech sensors and automated devices, some of which were developed exclusively for the HOPE project. This 8.5 meters high and 5 meters in diameter platform, is completely self-sufficient in energy, powered by solar panels and wind turbines. The buoy works in tandem with six 700m-long instrumented fixed mooring lines, forming an oceanographic measurement system covering an area of over 2km2 in the ocean - one of the most extensively instrumented oceanographic sites to date. The combined system measures the high-frequency variability (hourly and daily for several years) of plankton biodiversity, associated carbon fluxes and currents, simultaneously at the surface and in the deep ocean. This data will shed light on the complex processes involved in carbon sequestration by the ocean.
