Submarine venting of liquid carbon dioxide on a Mariana Arc volcano

Abstract

Although CO 2 is generally the most abundant dissolved gas found in submarine hydrothermal fluids, it is rarely found in the form of CO 2 liquid. Here we report the discovery of an unusual CO 2 ‐rich hydrothermal system at 1600‐m depth near the summit of NW Eifuku, a small submarine volcano in the northern Mariana Arc. The site, named Champagne, was found to be discharging two distinct fluids from the same vent field: a 103°C gas‐rich hydrothermal fluid and cold (<4°C) droplets composed mainly of liquid CO 2 . The hot vent fluid contained up to 2.7 moles/kg CO 2 , the highest ever reported for submarine hydrothermal fluids. The liquid droplets were composed of ∼98% CO 2 , ∼1% H 2 S, with only trace amounts of CH 4 and H 2 . Surveys of the overlying water column plumes indicated that the vent fluid and buoyant CO 2 droplets ascended <200 m before dispersing into the ocean. Submarine venting of liquid CO 2 has been previously observed at only one other locality, in the Okinawa Trough back‐arc basin (Sakai et al., 1990a), a geologic setting much different from NW Eifuku, which is a young arc volcano. The discovery of such a high CO 2 flux at the Champagne site, estimated to be about 0.1% of the global MOR carbon flux, suggests that submarine arc volcanoes may play a larger role in oceanic carbon cycling than previously realized. The Champagne field may also prove to be a valuable natural laboratory for studying the effects of high CO 2 concentrations on marine ecosystems.