Transport and speciation of hydrothermally derived metals (e.g. Fe and Zn) from different island arc systems and mid-ocean ridges

Iron (Fe) and zinc (Zn) represent limited but essential micronutrients within the marine biogeochemical cycle in most oceans. For many years, hydrothermal vents were neglected as sources of dissolved metals into the oceans. However, ongoing research has shown that Fe is introduced to the world oceans and stabilized at elevated concentrations by hydrothermal venting, potentially transported thousands of kilometers away from its original source into the distal oceans, thereby contributing to the global oceanic metal budget. This is due to both inorganic (e.g. as sulfide nanoparticles) as well as organic complexation by small metal chelating molecules – so called organic ligands. Island arc hydrothermalism occurs at much shallower water depths than hydrothermalism at mid-ocean ridges. Hence, dissolved stabilized bioactive trace metals may be transported into the photic zone, the area of highest primary production rates in the ocean. There, hydrothermally derived metals may serve as essential micronutrients (Fe and Zn) or potential toxins (Al or Cu) to marine organisms, such as phytoplankton. Island arc hydrothermalism has not gained much attention thus far. In our ongoing projects related to RV SONNE cruises into the SW Pacific, SO253 (Kermadec Arc) and SO263 (Tonga Arc), we show that the role of this process in the oceans’ biogeochemical cycle of metals and the metals’ bioavailability may have been underestimated to date.

Contacts: Charlotte Kleint, Andrea Koschinky