First results from a controlled deep sea CO2 perturbation experiment:
Evidence for rapid equilibration of the oceanic CO2 system at depth

Noriko Nakayama
Ocean Research Institute, University of Tokyo, Tokyo, Japan

Edward T. Peltzer, Peter Walz, and Peter G. Brewer
Monterey Bay Aquarium Research Institute, Moss Landing, California, USA

Journal of Geophysical Research (2005) 110, C09S11, doi:10.1029/2004JC002597.

Received: 2004 July 15.
Revised: 2005 January 31.
Accepted: 2005 April 14.
Published: 2005 August 23.


ABSTRACT

We have carried out series of remotely operated vehicle–controlled oceanic CO2 system perturbation experiments off the coast of California at depths down to 1000 m to observe reaction rates and pathways with both HCl and HCO3¯ addition. The work was done to evaluate possible barriers to carrying out future Free Ocean CO2 Enrichment experiments to simulate the chemistry of the emerging high CO2–lower pH ocean. A looped 460 mL flow cell with a pH sensor was used to monitor the time to equilibrium for 900 µL additions of 0.008 N HCl and for small slugs of HCO3¯ enriched seawater. The results were compared to equivalent experiments at the same temperature and 1 atm pressure. In each case the experiments at depth showed significantly faster time to equilibrium than those at 1 atm. These results are consistent with the low partial molal volume of CO2 in seawater, favoring the hydration reaction rate. The results imply, but do not prove, a significant effect of pressure on the rate constants. The relatively rapid equilibration times observed in seawater of 4°C and at 10 MPa indicates that there are no fundamental physical chemistry limits for carrying out small-scale free-ocean CO2 enrichment experiments.

© 2005 by the American Geophysical Union.


Acknowledgements

This work would not have been possible without the efforts of the captain and crew of the R/V Point Lobos and the skilled work of the pilots of the ROV Ventana. The manuscript benefited from the careful work of two anonymous reviewers. D. Wolf-Gladrow has pointed out that the strong correlation of carbonate ion decrease with depth may also account for a chemical kinetic enhancement of rates. We acknowledge the support of the David and Lucile Packard Foundation to MBARI. The participation of Noriko Nakayama was made possible by a Research Fellowship from the Japan Society for the Promotion of Science. Support was provided by an International Research Grant from the New Energy and Industrial Technology Organization (NEDO) and the U.S. Dept. of Energy Ocean Carbon Sequestration Program (grants DE-FC26-00NT40929 and DE-FC03-01ER6305).


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