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 similar to 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 similar to 0.2-0.6% of the annual estimated output of CO2 from all subaerial arc volcanoes, and similar to 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.