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 mu m; 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 0-1500m depth) by ocean currents, thereby potentially stimulating surface ocean primary productivity. Hydrothermal Fe oxyhydroxide particles (>0.2 mu m) 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. Key Points A large portion of iron from hydrothermal island arc calderas exists as colloids These colloids coprecipitate important amounts of dissolved oxyanions Iron colloids from hydrothermal island arcs may stimulate primary productivity