NOAA Research 2007 Outstanding Scientific Paper Awards

“Submarine venting of liquid carbon dioxide on a Mariana Arc volcano”

John Lupton, David Butterfield, Marvin Lilley, Leigh Evans, Ko-ichi Nakamura, William Chadwick Jr., Joseph Resing, Robert Embley, Eric Olson, Giora Proskurowski, Edward Baker, Cornel de Ronde, Kevin Roe, Ronald Greene, Geoff Lebon, Conrad Young

ABSTRACT
Although CO₂ is generally the most abundant dissolved gas found in submarine hydrothermal fluids, it is rarely found in the form of CO₂ liquid. Here we report the discovery of an unusual CO₂-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 CO₂. The hot vent fluid contained up to 2.7 moles/kg CO₂, the highest ever reported for submarine hydrothermal fluids. The liquid droplets were composed of ∼98% CO₂, ∼1% H₂S, with only trace amounts of CH₄ and H₂. Surveys of the overlying water column plumes indicated that the vent fluid and buoyant CO₂ droplets ascended <200 m before dispersing into the ocean. Submarine venting of liquid CO₂ 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 CO₂ 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 CO₂ concentrations on marine ecosystems. FULL TEXT

Diagram showing a model proposed for the gas flux from NW Eifuku, in which a CO2-rich gas is directly degassing from the magma chamber

Diagram showing a model proposed for the gas flux from NW Eifuku, in which a CO₂-rich gas is directly degassing from the magma chamber. As this hot gas rises through the system, it cools, and CO₂ condenses as a separate liquid phase on the periphery of the main conduit. Seawater circulates through the system, but the penetration of water into the core of the system is limited at temperatures below 250°C due to CO₂-H₂O immiscibility. At the volcano summit the liquid CO₂ collects beneath a hydrate "cap" layer that forms where the liquid CO₂ comes in contact with seawater. Because the penetration of water is limited and the enthalpy is carried by the CO₂ gas, there is little high-temperature water-rock interaction. (larger image)

(a) Chart comparing δ¹³C (‰) for CO₂ from various MOR sites [Kelley et al., 2004], the Okinawa Trough [Sakai et al., 1990a, 1990b], NW Eifuku (this work), marine carbonates [Hoefs, 1980], and typical volcanic arcs [Sano and Williams, 1996; van Soest et al., 1998]. (b) Similar chart comparing CO₂/³He ratios for MOR vents [Kelley et al., 2004], the Okinawa Trough [Sakai et al., 1990a, 1990b], and typical volcanic arcs [Sano and Williams, 1996; van Soest et al., 1998]. (larger image)

(a) Location map for NW Eifuku in the Mariana Arc. (b) Oblique 3-D representation of NW Eifuku viewed from the southwest, generated from EM300 bathymetry. No vertical exaggeration. Depths range from 1550 to 3000 m. (larger image)

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