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National Oceanic and Atmospheric Administration
Atmospheric Chemistry Group

PMEL-JISAO Trace Gas Program

Cruise tracks figureProgram description
Summary of research accomplishments
Summary of available data

PMEL-JISAO Trace Gas Program Description

The goals of the PMEL-JISAO Trace Gas program are to determine:

The ship-based transects yield ocean-scale distributions of key species which can be used to test and validate trace gas sources, sinks and transport in GCMs. The program to date has focused on CO, CH4, OCS and O3. CO and CH4 data are available for a series of 8 cruises throughout the Pacific Ocean (1987- 1994) and can be accessed via this server.

PMEL-JISAO Trace Gas Program Accomplishments

PMEL-JISAO Trace Gas Program Available Data

The data can be accessed HERE.

Cruise Descriptions

The data compiled here include carbon monoxide and methane measurements made by PMEL-JISAO in the surface ocean and overlying atmosphere on eight cruises in the Pacific and Indian Oceans between 1987 and 1994:

The cruises include:



Gas partial pressures were measured continuously in surface seawater along the cruise tracks using an equilibrator system designed to partition dissolved gases into a vapor phase for sampling. The equilibrator was fed with seawater pumped directly to the laboratory area from an intake located at approximately 5 m depth near the bow of the ship. The equilibrator was constructed from Plexiglass and consisted of a 20 L enclosed headspace continuously showered with 15-20 L/min of seawater. Approximately every hour, 2 ml of gas were withdrawn from the headspace for analysis.

Air samples were pulled from the bow of the ship, 10 m above the sea surface, to the oceanographic laboratory (approximately 40 m) through plastic coated aluminum tubing (Dekoron) at a flow rate of 10 L/min. Dekoron tubing was also used to connect the equilibrator to the analytical system.


Gas partial pressures were measured with an automated, temperature controlled, gas chromatographic system containing both a flame ionization detector (FID) and a mercury bed detector (MBD). Air samples from the air sampling line, the equilibrator, or a standard stream were dried using phosphorous pentoxide or potassium permanganate and drawn into a 2 ml sample loop connected to an automated sample valve. The gases were separated using a series of five columns with CO valved to the MBD and CH4 valved to the FID. The system was automated with a Carle Series 400 Controller and ran unattended with alternating injections of air, standard, and equilibrated air with the series repeated approximately each hour.

Data Reduction

The raw signals were first visually filtered to eliminate any episodes of ship contamination or instrument malfunction. CO and CH4 mixing ratios in both air and equilibrator samples were then computed based on peak height (CH4) or peak area (CO) and a six-hour running-mean single or dual-point standard. The CH4 data were further smoothed using a 12 hour weighted regression. The dry-air mixing ratios were then binned into hourly values based on the measurements made 30 minutes before and after the hour. The partial pressures measured in the equilibrator samples were corrected for warming during transit from the water intake to the equilibrator using a ratio of the seawater solubilities at sea surface temperature and the equilibrator temperature. The warming values were derived from the regression of hourly warming on sea surface temperature.

Standards were dried, whole-air mixtures contained in aluminum cylinders and were calibrated by NOAA/CMDL. CO and CH4 mixing ratios are referenced to the CMDL and Rasmussen scales, respectively. The accuracy of the standards, as determined by CMDL is ± 2% and ± 1.5% for CO and CH4, respectively. During these cruises the instrument precision, as determined by the average percent standard deviation of the standard response over a six hour period, was approximately ± 1.5% and ± 1.8% for CO and CH4, respectively.

Data Summary

The data from each cruise are available in ascii form in 16 columns:

The gas data are the mole fraction dry gas concentrations. Missing data are denoted with a -9.

The data can be accessed HERE.

Last update: 13 November 1996

Atmospheric Chemistry Group PMEL