Monterey Bay Aquarium Research Institute
The Emerging Science of a
High CO2 / Low pH Ocean


Chemistry Overview

Chemistry Team Members

The primary goal of the Chemistry Team within the High CO2 Project is to understand the chemical changes in the ocean associated with the CO2 enrichment of seawater. While the equilibrium chemistry of the carbonate system is widely known, the kinetics of the reaction of CO2 with seawater presents a new set of challenges. In the ocean at large, the kinetics of the carbonate system are of minor concern because sufficient time exists for equilibrium to be achieved. However, for a short-term process like the flow-through FOCE experiment, little time is available for the reactions to come to completion. Consequently, an understanding of the kinetics of the CO2 system is essential knowledge to the successful execution of any experiment. This has been our first area of interest.

Beyond the kinetics of the carbonate system, there are several additional areas of interest:

  • Amplification of the anthropogenic pCO2 signal in the mid-water.
  • Impact of the changes in pH on the propagation of sound in the ocean.
  • Synergistic effects of rising pCO2 and reductions in pO2 (due to global warming and decreased deep water ventilation) on oxic respiration at mid-ocean depths.

ROV based seawater titration equipment

In the figure above (left) we see the apparatus for the CO2 kinetic studies mounted on ROV Ventana. The titration cell, pH sensor, hydraulic valves and syringes are mounted on the swing-arm. Reservoirs of reference seawater can be see strapped in place on the front porch. The close-up view on the right shows the titration cell with pH sensor, the two hydraulic syringes with acid bags and the SeaBird pump. By ativating the hydraulic valves, we could open the titration cell and flush it with ambient seawater or the reference seawater solution. Alternatively, the valves could be set to the "closed" position, where the pump continuously re-circulates the solution within the cell providing a very effective stirring mechanism.

CO2 Kinetic Experiment Data display

The lefthand figure above shows a framegrab from a sewater titration experiment designed to studythe kinetics of the CO2 hydration reaction. Three equal volume injections were made resulting in the three not so equal downward steps. At the end of the sequence, the cell flushing valves were opened and the titration cell was flushed with ambient seawater and a rapid recovery in pH was observed. The righthand figure shows a fit of the pH data (here expressed as hydroxide ion concentration) to an exponential curve. The exponent of this expression is proportional to the kinetic rate constant of the CO2 hydration reaction.

See also:  Ocean Chemistry of Greenhouse Gases Web Page

Questions? Comments? Please contact Edward Peltzer.
Last updated: Jul. 17, 2013