Introduction
January 1996 marked the completion of a 14-month, 92,000 km-long hydrographic survey of the Indian Ocean by the World Ocean Circulation Experiment (WOCE) Hydrographic Programme (WHP) (Fig.1). In addition to the standard WOCE hydrographic parameters measured on these cruises, discrete and underway carbon measurements were made by members of the carbon dioxide (CO2) survey team. The survey team is a part of the Joint Global Ocean Flux Study (JGOFS) supported by the U.S. Department of Energy (DOE) to make carbon system measurements on the WOCE global survey cruises. As part of the survey team, the Princeton University (PU) Ocean Tracers Laboratory (OTL) constructed an automated system for underway analysis of surface water and marine air CO2 concentrations (hereafter referred to as the underway system). With the help of the other science team members, the underway system was run aboard Research Vessel (R/V) Knorr during all nine legs of the Indian Ocean survey. All measured data and documentation are available to the public through the Carbon Dioxide Information Analysis Center (CDIAC). This report provides a description of the data files, underway system as well as a brief explanation of when and where the data were collected, any problems encountered with the system, and how the data can be accessed through CDIAC.
The underway system was installed by R. M. Key of Princeton University on the R/V Knorr in November 1994, prior to the first leg of the survey. Table 1 lists the chief scientist, cruise dates, ports of call, affiliation of the group responsible for discrete carbon sampling, and the analyst in charge of operating the underway system for each of the Indian Ocean legs. On all legs except the first, the CO2 analyst responsible for operating the underway system was a member of the OTL group.
Table 1. Information on individual legs of WOCE Indian Ocean Survey
| WOCE section | Chief scientist | Cruise dates | Ports of call | Carbon group | Underway system analyst |
|---|---|---|---|---|---|
| I8S/I9S | M. McCartney | 12/01/94 01/19/95 | Fremantle, AU Fremantle, AU | BNL1 | K. Johnson |
| I9N | A. Gordon | 01/24/95 03/06/95 | Fremantle, AU Colombo, Sri Lanka | PU2 | C. Sabine |
| I8N/I5E | L. Talley | 03/10/95 04/06/95 | Colombo, Sri Lanka Fremantle, AU | UH3 | G. McDonald |
| I3 | W. Nowlin | 04/23/95 >06/05/95 | Fremantle, AU Mauritius | UM4 | R. Key |
| I5W/I4 | J. Toole | 06/11/95 07/11/95 | Mauritius Mauritius | BNL | T. Key |
| I7N | D. Olson | 07/15/95 08/24/95 | Mauritius Muscat, Oman | UH | T. Zahn |
| I1 | J. Morrison | 08/29/95 10/16/95 | Muscat, Oman Singapore | WHOI5 | R. Rotter |
| I10 | N. Bray | 11/11/95 11/28/95 | Dampier, AU Singapore | PU | T. Key |
| I2 | G. Johnson | 12/02/95 01/22/96 | Singapore Mombasa, Kenya | UH | A. Dorety |
1Brookhaven National Laboratory;
2Princeton University;
3University of Hawaii;
4University of Miami;
5Woods Hole Oceanographic Institution.
A majority of the data are of excellent quality. The only major technical problems were encountered on the first leg as a result of failures in the ship's seawater supply system. Approximately 10 days after the R/V Knorr departed Fremantle, Australia, for the first leg of the survey, the ship encountered heavy weather that resulted in frequent shutdowns of the ship's uncontaminated seawater pump. On December 19, 1994, the seawater supply for the underway system was switched to a secondary seawater pump. Post-cruise examination of the data revealed that the water from this pump had undergone significant heating, presumably the result of a long (and apparently variable) residence time in the ship. The underway temperature and salinity values recorded during this time are also questionable because they do not track very well with the surface temperature and salinity measured by a conductivity, temperature, and depth sensor (CTD). After careful analysis, much of the data had to be flagged as bad, and the remaining data are much "noisier" than data from subsequent legs. The original uncontaminated seawater supply was back on-line for the second leg and operated with only minor outages for the remainder of the survey. By the end of the survey on January 22, 1996, nearly 250,000 individual measurements of surface water and atmospheric mole fraction of CO2 (xCO2) 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 and were associated with the southwest monsoon upwelling.
This report provides details on the calibration and quality control procedures followed in the production of this data set. An extensive account of specific events potentially affecting the CO2 underway system has been compiled from the original notebooks and is included in Appendix B. The major events are briefly described in the Results section, but a number of minor events (e.g., times when the drying column was changed), which did not appear to have a direct effect on the results, are only recorded in the Appendix B. For further details on additional measured parameters and the objectives of each leg see the individual WOCE cruise reports produced by the chief scientist (http://woce.nodc.noaa.gov/wdiu/).
