Although CO is generally the most abundant dissolved gas found in submarine hydrothermal fluids, it is rarely found in the form of CO liquid. Here we report the discovery of an unusual CO-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. The hot vent fluid contained up to 2.7 moles/kg CO, the highest ever reported for submarine hydrothermal fluids. The liquid droplets were composed of ~98% CO, ~1% HS, with only trace amounts of CH and H. Surveys of the overlying water column plumes indicated that the vent fluid and buoyant CO droplets ascended <200 m before dispersing into the ocean. Submarine venting of liquid CO 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 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 concentrations on marine ecosystems.
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