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, neither of which is completely understood, as well as the biological processes of photosynthesis and respiration. The oceans are estimated to hold 38,000 gigatons of carbon, 50 times more than that in the atmosphere and 20 times more than that held by 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, more than 15 times as much CO₂ is exchanged across the sea surface than the amount 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 already been conducted, and others are currently 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 multi-agency U.S. effort is led by the National Science Foundation and 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 the 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 include estimation of the meridional transport of inorganic carbon in the Pcific 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 the 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 40-day Leg 2 of the Research Vessel (R/V) Thomas Washington TUNES Expedition (TUNES-2) along the WOCE Sections P17S and P16S, which are located in the central part of the South Pacific Ocean along the 135^oW (between 6^oS and 33^oS) and 150^oW (between 17.5^oS and 37.5^oS) meridians respectively.

In addition to TCO₂, parameters measured include total alkalinity (TALK); discrete partial pressure of CO₂ (pCO₂) measured at 20^oC; pressure, temperature, salinity, and oxygen measured by conductivity, temperature, and depth sensor (CTD); bottle salinity; oxygen; nutrients; chlorofluorocarbons (CFCs); tritium; and helium.

Scientists from the following institutions participated in the cruise: Scripps Institution of Oceanography (SIO), Woods Hole Oceanographic Institution (WHOI), Lamont-Doherty Earth Observatory (LDEO), Rosenstiel School of Marine and Atmospheric Science (RSMAS), University of Hawaii (UH), and Princeton University (PU).

The CO₂ investigation during the TUNES-2 Expedition was supported by a grant (No. DE-FGO2-90-ER60983) from the U.S. DOE.