WP 3 : Hydrothermal plume modelling and dispersion of key biogeochemical compounds
The fate of these geochemical elements is poorly understood. They can be transported over long distances by ocean currents (e.g. several thousands of kilometers across the Pacific Ocean for instance), used as nutrients by the living world (biosphere), or sink to the ocean floor. The study of their transport and transformation on a global scale, known as the biogeochemical cycle, therefore request to address specifically to the roles of hydrothermal vents. In particular, we need to understand better the short-and-middle-term fate of geochemical compounds released from these vents. Where are they transported to? How much of them sink? Are they used (consumed) by certain living organisms and how? Several preliminary studies in ocean physics have shown that eddies populate the deep ocean, sort of giant vortices that can trap elements on the ocean floor and transport them over long distances. Although we initially believed that they were confined to the surface, tidal currents also seem to play a role in generating vertical exchanges, even at great depths. However, these physical questions have not been addressed in the case of hydrothermal vent and the geochemical compounds they discharge.
To address these issues, this WP3 will develop a tool, called a numerical regional circulation model, which simulates the fate of some chemical elements released from hydrothermal vents. This model is like a virtual swimming pool on which we blow wind to generate oceanic currents, we heat it from above to create a stratification between warm water at the surface and cold water at the bottom. Realistic underwater mountains are added to constrain the currents, creating specific deep channels, and the whole pool is shaken to generate oscillating tidal currents! Geochemical elements are then added to the vent sites, and these chemicals are then transported by the currents. Since we know some of the transformations that will affect these chemicals, the model will allow us to predict its concentration and its evolution along the way as it is transported. This numerical experiment will be carried out for a sufficiently long period of time to obtain a statistical view of the fate of biogeochemical compounds. We therefore hope to gain a better understanding of the role of hydrothermal vents in the global biogeochemical cycles of iron, manganese, and methane.
| The distribution of dissolved iron (nmol/kg−1) in the Atlantic Ocean from the GEOTRACES intermediate data product 2014 (Schlitzer, 2014). Hydrothermal plumes with elevated iron concentration are highly visible |
Distribution du fer dissous (nmol kg-1) dans l’océan Atlantique obtenue à partir du produit intermédiaire de données GEOTRACES (Schlitzer, 2014). Les panaches présentant des anomalies de concentration en fer au niveau des dorsales sont très visibles