Impacts of hydrothermal plume processes on oceanic metal cycles and transport

Characterization of hydrothermal plumes in terms of redox, rather than distance from the vent, illuminates the dominant transport processes and fate of metals, focusing on iron and manganese. Chemical, physical and biological processes in hydrothermal plumes control the flux of elements from hydrothermal vents to the global oceans. The timescales of these processes range from less than a second, as the hydrothermal fluid mixes with seawater at the seafloor, to decades, as the plume disperses over thousands of kilometres. Integrating hydrothermal geochemistry throughout the lifetime of the plume reveals some well-constrained processes, along with many surprises. For instance, contrary to the idea that metals are removed from the hydrothermal plume via oxidation, a survey of recent datasets reveals that oxidation of iron and manganese does not consistently result in their removal from the plume, and that manganese may be lost from the water column more rapidly than iron. These observations suggest that our understanding of element transport in hydrothermal plumes is incomplete, partly due to the change in removal processes as the plume disperses from less than 1 km from the vent to more than 4,000 km. We suggest that characterizing the plume on the basis of regions that retain some reduced components versus those that are fully oxidized, in addition to buoyancy, will illuminate the nature of the dominant processes and allow a more complete understanding of the ultimate fate of hydrothermally derived metals.