Abstract

This data documentation presents the results of the surface water and atmospheric underway measurements of mole fraction of carbon dioxide (xCO₂), sea surface salinity, and sea surface temperature, obtained during the World Ocean Circulation Experiment (WOCE) Indian Ocean survey cruises (December 1994­January 1996). Discrete and underway carbon measurements were made by members of the CO₂ survey team. The survey team is a part of the Joint Global Ocean Flux Study supported by the U.S. Department of Energy to make carbon-related measurements on the WOCE global survey cruises.

Approximately 200,000 surface seawater and 50,000 marine air xCO₂ measurements were recorded. Seawater values ranged from 310 ppm to greater than 610 ppm. The lowest values (~50 ppm below atmospheric) were measured in the southwestern Indian Ocean, south of Madagascar. The highest values (more than 250 ppm higher than atmospheric) were found in the Arabian Sea associated with the southwest monsoon upwelling.

All measurements were made using the new fully automated system, designed by the scientists of the Princeton University Ocean Tracers Laboratory. This system was continuously running during all nine Indian Ocean cruises aboard Research Vessel Knorr. The system (fully described in Appendix A of this documentation) had a response time of ~1 min and a long-term precision and accuracy of ~0.4 and 1 ppm, respectively. The equilibrator design is a modification of a counterflow disk stripper that has been used in the past to extract soluble gases from seawater. The detector is a dual-beam infrared spectrometer. Calibration and operation of the instrument as well as data logging are computer controlled and require minimal attention. The design is such that other instrumentation can be easily added. Details of the instrument control, calibration, and efficiency tests for this instrument are given to assist others interested in building similar-type systems.

The Indian Ocean underway CO₂ data set is available free of charge as a numeric data package (NDP) from the Carbon Dioxide Information Analysis Center. The NDP consists of twenty data files, two FORTRAN 77 routines, a readme file, and this printed documentation. The data files and html version of this report can be accessed through the following World Wide Web site: /oceans/doc.html.

Reference

• Sabine, C. L., and R. M. Key. 1997. Surface Water and Atmospheric Underway Carbon Data Obtained During the World Ocean Circulation Experiment Indian Ocean Survey Cruises (R/V Knorr, December 1994­January 1996). ORNL/CDIAC-103, NDP-064. Carbon Dioxide Information Analysis Center,Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tennessee. doi: 10.3334/CDIAC/otg.ndp064.