The importance of shallow hydrothermal island arc systems in ocean biogeochemistry

Hydrothermal venting often occurs at submarine volcanic calderas on island arc chains, typically at shallower depths than mid–ocean ridges. The effect of these systems on ocean biogeochemistry has been under-investigated to date. Here we show that hydrothermal effluent from an island arc caldera was rich in Fe(III) colloids (0.02–0.2 µm; 46% of total Fe), contributing to a fraction of hydrothermal Fe that was stable in ocean water. Iron(III) colloids from island arc calderas may be transferred into surrounding waters (generally 0–1500 m depth) by ocean currents, thereby potentially stimulating surface ocean primary productivity. Hydrothermal Fe oxyhydroxide particles (>0.2 µm) were also pervasive in the studied caldera and contained high concentrations of oxyanions of phosphorus (P), vanadium (V), arsenic (As), and manganese (Mn). Hydrothermal island arcs may be responsible for > 50% of global hydrothermal P scavenging and > 40% V scavenging, despite representing <10% of global hydrothermal fluid flow.