Crystallization of nano-scale hydrothermal iron particles: long-range hydrothermal Fe transport and its role in ocean chemistry.

Seafloor hydrothermal vents emit essential trace metals such as iron into the (deep) ocean. A key topic is the fate and transport range for this hydrothermal iron, to better understand its impact on the ocean nutrient inventory. Evidence is emerging that silicon coprecipitation and complexation with organic matter extend the lifetime of Fe in the ocean. We collected iron-rich nanoparticles and aggregates from one of the most iron-rich hydrothermal plumes know so far in the mid-Atlantic Rainbow vent field. We characterized the particles in detail with micro(spectro)scopy (TEM) and chemical methods. Sub-samples were then used in an aging experiment, to monitor changes to the iron particles and their interaction with seawater. Marked changes in particle morphology and chemistry occurred and we propose to use Fe K-edge EXAFS to determine the structural evolution. Our results will further elucidate how hydrothermal iron behaves in the global ocean and to what extent it becomes bioavailable.