Background Information

There is currently much interest in understanding the inorganic carbon dioxide (CO₂) system in the oceans. This is due to the increasing atmospheric concentration of CO₂ enhancing the earth-atmosphere system's natural greenhouse effect and potentially affecting the earth's climate. Approximately 40% of the CO₂ added to the atmosphere as a result of the burning of fossil fuels is thought to be in turn absorbed by the oceans. The flux of carbon dioxide across the air-sea interface is controlled by the difference in the partial pressure of CO₂ in the atmosphere and in the surface waters. Once the CO₂ is in solution it can equilibrate with the bicarbonate and carbonate ions. The carbonate ion concentration in the oceans controls the rate of precipitation and dissolution of calcium carbonate (CaCO₃) in the oceans. The carbon dioxide system can be characterized by measuring two of the four measurable parameters [pH, the fugacity of CO₂ (fCO₂), the total carbon dioxide (TCO₂), and the total alkalinity (TALK)]. The other parameters can be calculated using thermodynamic relations.

To learn more about the role of the world ocean in climate dynamics, several large ocean experiments have been conducted. The World Ocean Circulation Experiment (WOCE) is the largest such experiment ever attempted. A major component of the World Climate Research Program (WCRP), WOCE brings together scientists from more than 30 nations. Although TCO₂ is not an official WOCE measurement, carbonate chemists are participating in the WOCE cruises as part of the Joint Global Ocean Flux Study (JGOFS) to measure the components of the carbon dioxide system in the oceans. These studies are being sponsored in the United States by the U.S. Department of Energy (DOE) and the National Oceanographic and Atmospheric Administration (NOAA). The carbon dioxide system parameters measured, in order of preference, are the TCO₂, TALK, and pH. Preferred analytical methods are coulometery for TCO₂, titration for TALK, spectroscopy for pH, and infrared (IR) or gas chromatography (GC) for fCO₂. Because coulometry and IR or GC systems to measure TCO₂ and fCO₂, respectively, were not available on the R/V Hespérides cruise, and because only one berth was available, the TALK, TCO₂, and pH were determined by titration. Although this is not ideal, it was believed that some reasonably precise data were better than no data.

The present report gives the results of carbonate measurements made during the 32 days of the expedition of the R/V Hespérides along WOCE section A5 (along 24.5° N) (Fig. 1).