科研之友
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摘要
An autonomous system using isotope dilution as its core method has been developed to obtain high-frequency measurements of dissolved inorganic carbon (DIC) concentrations in the surface ocean. This system accurately mixes a seawater sample and a C-13-labeled sodium bicarbonate solution (spike). The mixed solution is then acidified and sent through a gas permeable membrane contactor. CO2 derived from DIC in the mixture is extracted by a CO2-free gas stream, and is sent to a cavity ring-down spectrometer to analyze its C-13/C-12 ratio. [DIC] of the seawater can then be derived from the measured C-13/C-12, the known mixing ratio and the [(DIC)-C-13] of the spike. The method has been tested under a wide [DIC] range (1800-2300 mu mol/kg) in the laboratory. It has also been deployed on a cruise that surveyed ocean waters to the south of Florida. At a sampling resolution of 4 min (15 samples per hour), the relative standard deviation of DIC determined from the laboratory tests and the field deployment is +/- 0.07% and +/- 0.09%, respectively. The accuracy of the method is better than 0.1% except where [DIC] varies faster than 5 mu mol/kg per minute. Based on the laboratory and field evaluations, we conclude that this method can provide accurate underway [DIC] measurements at high resolution in most oceanic regions.
- 出版日期2013-11
