Reference Materials for Oceanic Carbon Dioxide Measurements

by Andrew G. Dickson, University of California, San Diego

A major goal of modern oceanography is the coordinated study of oceanic processes on a global scale. The impetus comes from a desire to understand the factors that control climate and how climate changes affect biogeochemical systems. In particular, a clear grasp of the circulation of the oceans, as well as the associated physical processes and their biological, geological, and chemical consequences, is needed.

One of the first questions that should be asked about the analytical measurements in such global studies is: How reliable are they? This has been a principal concern of the Joint Global Ocean Flux Study (JGOFS) program, which required that measurements made at different times, by different scientists, from different laboratories, both in the United States and abroad, be comparable and correct; reliability will be an important factor in the design of any global ocean observing system.

Although the study of the oceanic carbon dioxide system has been going on for over 120 years, assuring the quality and comparability of measurements is still difficult today. However, a major advance has recently been made: certified reference materials are now available for the measurement of total dissolved inorganic carbon and total alkalinity in sea water.

Reference materials are stable substances for which one or more properties have been established sufficiently well to calibrate a chemical analyzer or to validate a measurement process. The ideal reference material for oceanic carbon dioxide studies is a sterilized natural sea water that has been assayed for the various carbon system parameters and that remains stable once packaged.

My laboratory (in collaboration with that of Dr. C. D. Keeling) has been supported by the U.S. National Science Foundation since 1989 to develop methods to prepare and certify such materials. Twenty thousand bottles of reference materials have now been distributed to a wide variety of laboratories both within the United States and in nineteen other countries. They are used extensively to confirm that instruments are performing properly and to ensure measurement compatibility. The U.S. Department of Energy (DOE) recognized the value of such a program and actively incorporated the use of reference materials as part of the quality assurance activities associated with its U.S. JGOFS Global Carbon Dioxide Survey (1991-1997). We supplied the seagoing investigators with reference materials and also helped to develop guidelines for their use as part of an overall quality control plan.

This focus on quality control is paying off handsomely. The oceanic carbon dioxide results obtained by the DOE-funded survey and by the various other U.S. JGOFS activities are of significantly higher quality than those of any previous study. Taken together, they will provide the basis for an unambiguous estimate of the fate of fossil fuel carbon dioxide in the oceans of the world to date, as well as offer needed insights into the workings of the oceanic carbon cycle.

(For more information about the Oceanic Carbon Dioxide Reference Materials Program, check the Web site

George Anderson bottling reference materials.

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