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Сопоставление результатов определения карбонатной системы и общей щелочности морской воды по данным различных аналитических методов

Морской гидрофизический журнал 01/2011;
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    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.
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    ABSTRACT: This work compares the classic Chen and Millero [1979] approach for estimating anthropogenic CO2 from ocean carbon measurements with the more recent DeltaC* technique used by Sabine et al. [1999] to estimate anthropogenic CO2 concentrations in the Indian Ocean. Application of the Chen technique to the WOCE/JGOFS Indian Ocean data set gives a total anthropogenic CO2 inventory that is essentially the same as the DeltaC* inventory, but there are substantial differences in the distributions within the water column. Some of these differences result from details of the application of the techniques such as the choice of which equation to use for the preformed alkalinity concentration or the choice of stoichiometric ratio to use for the biological correction. More significant differences, however, result from two fundamental differences in the techniques. One fundamental difference between the two techniques is that changes in the properties of the subsurface waters are referenced to a single deep water value in the Chen approach instead of the multiple reference points from the isopycnal analysis used in the DeltaC* approach. The second fundamental difference is in the estimation of the preindustrial TCO2 distribution. Many of the differences examined have counteracting effects that may result in a total anthropogenic CO2 inventory that is similar for the two techniques. However, this similarity does not imply that both approaches are right. Comparison with global carbon models and other measurement-based techniques do not clearly demonstrate that one technique is better than another. However, given the additional constraints of the transient tracers and the isopycnal analysis, we believe that the DeltaC* technique provides a more robust estimate.
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    ABSTRACT: The partial pressure of carbon dioxide in the ocean's surface waters, precisely expressed as the fugacity (fCO2) is determined from dissolved inorganic carbon (DIC) and total alkalinity (TA), and the first and second dissociation constants of carbonic acid, K1 and K2. The original measurements of K1 and K2 reported by Mehrbach et al. [Mehrbach, C., Culberson, C.H., Hawley, J.E., Pytkowicz, R.M., 1973. Measurement of the apparent dissociation constants of carbonic acid in seawater at atmospheric pressure. Limnol. Oceanogr. 18, 897–907] are reformulated to give equations for pK1 and pK2 (pK=−log10K) as a function of seawater temperature and salinity, consistent with the “total hydrogen ion” concentration scale:By equilibrating solutions of seawater with gas mixtures of known composition, we demonstrate that the above formulations of K1 and K2 give calculated fCO2 values that agree with equilibrated values to 0.07±0.50% (95% confidence interval, fCO2 up to 500 μatm). Formulations of K1 and K2 based on other studies resulted in calculated fCO2 values approximately 10% lower than the measurements. Equilibrations at fCO2 above 500 μatm yielded measured fCO2 values higher than calculated values by on average 3.35±1.22% (95% confidence interval). The cause for the fCO2 dependence of the results is not known.The uncertainties in pK1 and pK2 were combined with the analytical uncertainties typical of contemporary measurements of DIC and TA to reveal the expected reliability of seawater fCO2 calculated from these parameters. For example, an uncertainty of 1.0 μmol kg−1 in DIC and 2 μmol kg−1 in TA (1 standard deviation (s.d.)) will result in uncertainty of the calculated fCO2 of 1% or ±3.5 μatm at 350 μatm (1 s.d.).
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