Hydrothermal fluid emanations from the submarine Kickʹem Jenny volcano, Lesser Antilles island arc

Little is known about the role of island arcs as hydrothermal sources to the ocean when compared to the extensive research that has been carried out on hydrothermal systems at spreading ridges, although increasingly more work is being done on intraoceanic arcs. Here, we present fluid geochemistry data from the Kickʹem Jenny (KeJ) submarine volcano of the Lesser Antilles island arc. Discharge of diffuse hydrothermal fluid was discovered on the southwestern flanks of the volcano. Hydrothermal input into the water column was recognized from CH4 and trace-metal anomalies in water-column profiles in a depth range of 500–700 m. Samples collected directly on the seafloor also showed evidence for hydrothermal emissions where Mg and Cl were depleted in the fluids compared to ambient seawater, while CH4 and several trace metals were enriched. The chemical composition of these samples, including O and H isotope data, suggests that the fluids are a mixture between a condensed vapor phase derived from a phase-separated hydrothermal fluid, which was conductively cooled in the sub-surface, and seawater. Increased dissolved organic carbon (DOC) concentrations of the fluids also indicate interaction with the sediment layer through which the fluids percolated. Although the volcanic crater could not be sampled directly due to safety concerns, δ3He and some trace-metal values in seawater samples indicate fluid input containing a mantle component, probably from a hot, focused-flow source in the crater region around 200–300 m depth.