Chemical Fluxes From a Recently Erupted Shallow Submarine Volcano on the Mariana Arc

Hydrothermal discharge from submarine arc volcanoes is thought to be an important contributor to global hydrothermal budgets, but quantitative flux measurements are scarce. Ahyi Seamount, a shallow (<100 m) submarine intraoceanic arc volcano located in the Commonwealth of the Northern Mariana Islands, erupted in May 2014. In May and December 2014, we sampled the hydrothermal plume created by the eruption and estimated chemical fluxes from Ahyi by combining shipboard hull-mounted Acoustic Doppler Current Profile current vector measurements with continuous and discrete Conductivity, Temperature, and Depth (CTD) data. Towed CTD sections were conducted perpendicular to the mean current direction: a sampling strategy that optimized chemical flux calculations by reducing complexities introduced by temporal variability in the speed and direction of plume dispersion. The Ahyi plume had an elevated optical backscatter signal accompanied by evidence of reduced chemical species and a lowered pH. We found enriched concentrations of H-2, He-3, CH4, particulate S, Mn, and Fe, observations consistent with a highly active hydrothermal system. The fluxes of magmatic He-3 and Fe from Ahyi were similar to that measured at three slow-spreading ridge-crest sites, whereas CH4 and Mn were 100-1,000 times lower. This is the first study to constrain export fluxes of a shallow submarine arc volcano into the euphotic zone. However, our data were collected soon after an eruption and thus may not be fully representative of the longer-term chemical inputs from Ahyi.