Flux measurements of explosive degassing using a yearlong hydroacoustic record at an erupting submarine volcano

The output of gas and tephra from volcanoes is an inherently disorganized process that makes reliable flux estimates challenging to obtain. Continuous monitoring of gas flux has been achieved in only a few instances at subaerial volcanoes, but never for submarine volcanoes. Here we use the first sustained (yearlong) hydroacoustic monitoring of an erupting submarine volcano (NW Rota-1, Mariana arc) to make calculations of explosive gas flux from a volcano into the ocean. Bursts of Strombolian explosive degassing at the volcano summit (520 m deep) occurred at 1-2 min intervals during the entire 12-month hydrophone record and commonly exhibited cyclic step-function changes between high and low intensity. Total gas flux calculated from the hydroacoustic record is 5.4 ± 0.6 Tg a^-1, where the magmatic gases driving eruptions at NW Rota-1 are primarily H₂O, SO₂, and CO₂. Instantaneous fluxes varied by a factor of ∼100 over the deployment. Using melt inclusion information to estimate the concentration of CO₂ in the explosive gases as 6.9 ± 0.7 wt %, we calculate an annual CO₂ eruption flux of 0.4 ± 0.1 Tg a^-1. This result is within the range of measured CO₂ fluxes at continuously erupting subaerial volcanoes, and represents ∼0.2-0.6% of the annual estimated output of CO₂from all subaerial arc volcanoes, and ∼0.4-0.6% of the mid-ocean ridge flux. The multiyear eruptive history of NW Rota-1 demonstrates that submarine volcanoes can be significant and sustained sources of CO₂ to the shallow ocean.