The HERMINE cruise is about to depart from Mindelo (Cape Verde) and return on April 29th in Las Palmas (Gran Canaria). Onboard the French oceanographic research vessel Pourquoi Pas ?, a team of 40 scientists will study the hydrothermal activity around the Trans-Atlantic Geotraverse (TAG) site (see map below).
Indeed, the hydrothermal activity along mid-ocean ridges is a fundamental process controlling the exchances of heat and chemial species between the ocean crust and seawater. Hydrothermal vents can serve as sources or sinks for many trace elements in the ocean. It has long been thought that iron and other trace metals were mostly removed in the vicinity of the vents, being incorporated into iron oxy-hydroxide or sulfide minerals, and thus not exported into the deep ocean. However, recent studies showed that iron can be stabilized in hydrothermal plumes and transported together with other trace metals, far across the ocean, up to thousands kilometers away from the vent source.However, little is known so far on the processes occurring from the fluid exit to the distal far-field non-buoyant plume, particularly in regions where seafloor massive sulfide (SMS) deposits are observed, such as at the vicinity of slow-spreading ridges and back-arc basins.
The Hydrothermal Exploration and Research for Mineralisation In New Environments (HERMINE) GEOTRACES process study (GPrA07) aims to answer at the following questions:
- What are the concentrations of metals, their physical (particulate/dissolved) and chemical (redox/organic/inorganic) speciation within the plume?
- What role do biogeochemical processes play in controlling trace element and gas distribution in hydrothermal plumes? What are the dispersal and biogeochemical reactivity of these elements?
- Can we establish a reliable baseline for the actual hydrothermal plume functioning, using a multiscale chemical and microbial mapping of hydrothermal plumes in order to further assess the potential impact of seabed mining?
Figure: Hermine cruise study site (©AS Alix, Ifremer)
Chief Scientist of the cruise: Y. Fouquet, C. Cathalot, and E. Pelleter
GEOTRACES scientists: H. Planquette, G. Sarthou, L.-E. Heimbürger, Catherine Jeandel