Background Information

The World Ocean Circulation Experiment (WOCE) Hydrographic Program (WHP) was a major component of the World Climate Research Program (WCRP). The primary WOCE goal was to understand the general circulation of the global ocean well enough to be able to model its present state and predict its evolution in relation to long-term changes in the atmosphere. The impetus for the carbon system measurements arose from concern over the rising atmospheric concentrations of carbon dioxide (CO₂). Increasing atmospheric CO₂ may intensify the earths natural greenhouse effect and alter the global climate.

Although CO₂-related measurements [total CO₂ (TCO₂), total alkalinity (TALK), partial pressure of CO₂ (pCO₂), and pH] were not an official WOCE measurements, a coordinated effort to make the carbon measurements was supported as a core component of the Joint Global Ocean Flux Study (JGOFS). This effort received support in the United States from the U.S. Department of Energy (DOE), the National Oceanic and Atmospheric Administration (NOAA), and the National Science Foundation (NSF) for WOCE cruises through 1998 to measure the global spatial and temporal distributions of CO₂ and related parameters. Goals were to estimate the meridional transport of inorganic carbon in a manner analogous to the oceanic heat transport (Bryden and Hall 1980; Brewer, Goyet, and Drysen 1989; Holfort et al. 1998; Roemmich and Wunsch 1985), and to build a data base suitable for carbon-cycle modeling and the estimation of anthropogenic CO₂ increase in the oceans. The CO₂ survey took advantage of the sampling opportunities provided by the WOCE cruises during this period, and the final data set was expected to cover on the order of 23,000 stations. Wallace (2002) recently reviewed the goals, conduct, and initial findings of the survey.

This report discusses the results of the research vessel (R/V) Knorr expedition along the WOCE Sections AR24, A24, A20, and A22 [cruises 147-2, 151-2, 151-3, and 151-4, respectively (Fig. 1)]. The latter three cruises not only were part of WOCE but also were a component of the Atlantic Circulation and Climate Change Experiment (ACCE). The ACCE was intended to improve the understanding of the entrainment and transformation of warm saline subtropical water into the subpolar North Atlantic waters, with special emphasis on sampling the North Atlantic Current region. This region plays an important role in the exchange of CO₂ between the subtropical and subpolar gyres. The exchange between these gyres affects the magnitude and direction of air-sea CO₂ exchange in the North Atlantic and is therefore an important factor in the global carbon cycle. By 1997 the goal of high-quality measurements of chemical and physical parameters had been completed in all of the major oceans except the North Atlantic. Hence the cruises documented here also represent the concluding phase of the DOE-sponsored Global CO₂ Survey.

The expedition (section AR24) started at Woods Hole, MassachusettsA, USA, on October 24, 1996, with a transit to the Azores; with the station work beginningbegan on November 2, 1996. The 1997 cruises started from Ponta Delgada, Azores, on May 30, 1997, and ended in Woods Hole on September 3, 1997, after stops in Halifax, N.S., Canada, and Port of Spain, Trinidad. The large-scale three-dimensional distribution of temperature, salinity, and chemical constituents, including the carbonate system parameters measured on these cruises (TCO₂, and TALK on the AR24 section and TCO₂, TALK, and pCO₂ on A24, A20, and A22 sections), will be plotted using the data from these sections. Knowledge of these parameters and their initial conditions will enable researchers to determine heat and water transport, as well as carbon transport, which will contribute to the understanding of processes affecting climate change. The sections described in this report include WOCE Section A22, the only Caribbean transect of the WOCE program. In addition, the stations occupied on these cruises repeated some sections sampled in previous years during the International Geophysical Year during the 1950s. They also included measurements from the eastern subpolar gyre of source and overflow waters from the Labrador, Norwegian, Greenland, and Iceland Seas. They give good coverage of boundary currents, particularly the Deep Western Boundary Current; and repeating AR24 and A24 provides some insight into seasonal variation in the North Atlantic.

This data documentation is the result of the cooperative efforts of chemical oceanographers from Brookhaven National Laboratory (BNL), the University of Hawaii (UH), Lamont-Doherty Earth Observatory (LDEO), and the University of Miamis Rosenstiel School of Atmospheric and Marine Science (RSMAS), U.S.A. The work aboard the R/V Knorr was supported by the U. S. Department of Energy under contract DE-ACO₂-76CH00016 and DE-FG02-93ER61540. The authors are also especially grateful to the Sonderforschungsbereich 460 at the University of Kiel (Dr. F. Schott, Leader), funded by the Deutsche Forschungsgemeinschaft, for their support and assistance in completing the written documentation.