Background Information

The World Ocean plays a dynamic role in the Earth's climate: it captures heat from the sun, transports it, and releases it thousands of miles away. These oceanic-solar-atmospheric interactions affect winds, rainfall patterns, and temperatures on a global scale. The oceans also play a major role in global carbon-cycle processes. Carbon is unevenly distributed in the oceans because of complex circulation patterns and biogeochemical cycles. The oceans are estimated to hold 38,000 gigatons of carbon, 50 times more than that in the atmosphere and 20 times more than plants, animals, and the soil. If only 2% of the carbon stored in the oceans were released, the level of atmospheric carbon dioxide (CO₂) would double. Every year, the amount of CO₂ exchanged across the sea surface is more than 15 times that produced by burning of fossil fuels, deforestation, and other human activities (Williams 1990).

To better understand the ocean's role in climate and climatic changes, several large experiments have been conducted, and others are under way. The largest oceanographic experiment ever attempted is the World Ocean Circulation Experiment (WOCE). A major component of the World Climate Research Program, WOCE brings together the expertise of scientists and technicians from more than 30 nations. In the United States, WOCE is supported by the federal government under the Global Change Research Program. The multiagency U.S. effort is led by the National Science Foundation and is supported by major contributions from the National Oceanic and Atmospheric Administration, the U.S. Department of Energy (DOE), the Office of Naval Research, and the National Aeronautics and Space Administration. Although total carbon dioxide (TCO₂) is not an official WOCE measurement, a coordinated effort, supported in the United States by DOE, is being made on WOCE cruises (through 1998) to measure the global, spatial, and temporal distributions of TCO₂ and other carbon-related parameters. The goal of the CO₂ survey includes estimation of the meridional transport of inorganic carbon in the Pacific Ocean in a manner analogous to the oceanic heat transport (Bryden and Hall 1980; Brewer et al. 1989; Roemmich and Wunsch 1985), evaluation of the exchange of CO₂ between the atmosphere and the ocean, and preparation of a database suitable for carbon-cycle modeling, and subsequent assessment of the anthropogenic CO₂ increase in the oceans. The final data set is expected to cover ~23,000 stations.

This report presents CO₂-related measurements obtained during the 42-day Leg 1 of the Research Vessel (R/V) Thomas Washington TUNES Expedition (TUNES-1) along the WOCE zonal Section P17C, which is located in the equatorial part of the Pacific Ocean along the 135° W meridian, between ~5° S and 36° N (Fig. 1).

The CO₂ investigation during the TUNES-1 Expedition was supported by a grant (No. DE-FGO2-90-ER60983) from DOE.