Small Scale Field Study of an Ocean CO2 Plume

• Published in: Journal of oceanography Vol. 60; no. 4; pp. 751 - 758
• Main Authors: Brewer, Peter G., Peltzer, Edward, Aya, Izuo, Haugan, Peter, Bellerby, Richard, Yamane, Kenji, Kojima, Ryuji, Walz, Peter, Nakajima, Yasuharu
• Format: Journal Article
• Language: English
• Published: Tokyo Springer Nature B.V 01.08.2004
• Subjects: Design; Electrodes; Fluid dynamics
• ISSN: 0916-8370; 1573-868X
• DOI: 10.1007/s10872-004-5767-9

We have carried out a small-scale (20 l) CO^sub 2^ sequestration experiment off northern California (684 m depth, 5°C, background ocean pH 7.7) designed as an initial investigation of the effects of physical forcing of the fluid, and the problem of sensing the formation of a low pH plume. The buoyant CO^sub 2^ was contained in a square frame 1.2 m high, exposing 0.21 m^sup 2^ to ocean flow. Two pH electrodes attached to the frame recorded the signal; a second frame placed 1.9 m south of the CO^sub 2^ pool was also equipped with two recording pH electrodes. An additional pH electrode was held in the ROV robotic arm to probe the fluid interface. Local water velocities of up to 40 cm sec^sup -1^ were encountered, creating significant eddies within the CO^sub 2^ box, and forcing wavelets at the fluid interface. This resulted in rapid CO^sub 2^ dissolution, with all CO^sub 2^ being depleted in a little more than 2 days. The pH record from the sensor closest (10 cm) to the CO^sub 2^ showed many spikes of low pH water, the extreme value being 5.9. The sensor 1 m immediately below this showed no detectable response. The electrodes placed 1.9 m distant from the source also recorded very small perturbations. The results provide important clues for the design of future experiments for CO^sub 2^ disposal and biogeochemical impact studies. These include the need for dealing with the slow CO^sub 2^ hydration kinetics, better understanding of the fluid dynamics of the CO^sub 2^-water interface, and non-point source release designs to provide more constant, controlled local CO^sub 2^ enrichments within the experimental area.[PUBLICATION ABSTRACT]