Peter G. Brewer,1 Edward Peltzer,1 Izuo Aya,2 Peter Haugan,3 Richard Bellerby,3
Kenji Yamane,2 Ryuji Kojima,2 Peter Walz1 and Yasuharu Nakajima4
1: Monterey Bay Aquarium Research Institute, Moss Landing, CA 95039, U.S.A.
2: Osaka Branch, National Maritime Research Institute, Osaka 576-0034, Japan
3: Geophysical Institute, University of Bergen, N-0057 Bergen, Norway
4: National Maritime Research Institute, Tokyo 181-0004, Japan
Journal of Oceanography (2004) 60: 751-758.
Received: 2003 September 29.
Revised: 2004 April 19.
Accepted: 2004 April 20.
We have carried out a small-scale (~20 l) CO2 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 CO2 was contained in a square frame 1.2 m high, exposing 0.21 m² to ocean flow. Two pH electrodes attached to the frame recorded the signal; a second frame placed 1.9 m south of the CO2 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 were encountered, creating significant eddies within the CO2 box, and forcing wavelets at the fluid interface. This resulted in rapid CO2 dissolution, with all CO2 being depleted in a little more than 2 days. The pH record from the sensor closest (~10 cm) to the CO2 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 CO2 disposal and biogeochemical impact studies. These include the need for dealing with the slow CO2 hydration kinetics, better understanding of the fluid dynamics of the CO2-water interface, and non-point source release designs to provide more constant, controlled local CO2 enrichments within the experimental area.
© 2004 by The Oceanographic Society of Japan.
We thank the pilots of the ROV Ventana for their skill and experimental assistance. This work would not have been possible without the support of an International Research Grant from the New Energy and Industrial Technology Organization (NEDO). We acknowledge the support at MBARI of the David and Lucile Packard Foundation, the U.S. Dept. of Energy Ocean Carbon Sequestration Program (Grants No. DE-FC26-00NT40929 and DEFC03-01ER6305).