An isotope dilution method for high‐frequency measurements of dissolved inorganic carbon concentration in the surface ocean. (4th November 2013)

• Record Type: Journal Article
• Authors: Huang, Kuan; Cassar, Nicolas; Wanninkhof, Rik; Bender, Michael
• Is Part Of: Limnology and oceanography, methods. Volume 11:Number 11(2013:Nov.)
• Page Start: 572
• Page End: 583
• Publication Date: 2013-11-04
• Subjects: Limnology -- Methodology -- Periodicals; Oceanography -- Methodology -- Periodicals; 551.48
• DOI: 10.4319/lom.2013.11.572
• Languages: English
• ISSNs: 1541-5856

Abstract

<abstract abstract-type="main"> <title> <x xml:space="preserve">Abstract</x> </title> <p>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 <sup>13</sup>C‐labeled sodium bicarbonate solution (spike). The mixed solution is then acidified and sent through a gas permeable membrane contactor. CO<sub>2</sub> derived from DIC in the mixture is extracted by a CO<sub>2</sub>‐free gas stream, and is sent to a cavity ring‐down spectrometer to analyze its <sup>13</sup>C/<sup>12</sup>C ratio. [DIC] of the seawater can then be derived from the measured <sup>13</sup>C/<sup>12</sup>C, the known mixing ratio and the [DI<sup>13</sup>C] of the spike. The method has been tested under a wide [DIC] range (1800–2300 µmol/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 µmol/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.</p> </abstract>