Résumé
We have measured both alkalinity and total carbon dioxide on a selected set of Black Sea samples from cruise 134 of R.V.
Knorr, using gas extraction/coulometry techniques, and improved titration procedures that permit more accurate data than those obtained in earlier expeditions. Earlier results had shown an apparent excess in alkalinity, by a factor of 1.6, from the stoichiometric ratio predicted from the sequential oxidation of Redfield ratio organic matter by the species O
2, NO
3
− and SO
4
2−. Thus both the nature of the organic substrate and our fundamental knowledge of reaction stoichiometry in anoxic systems were called into question. We show that the total CO
2 balance is consistent, within narrower limits than found earlier, with oxidation of organic matter by sulfate: 2CH
2O+SO
4
2− → 2HCO
3
−+H
2S and consistent with work on sediment interstitial waters in anoxic conditions (
Berner
et al., 1970,
Limnology and Oceanography,
15. 544–549:
Ben Yaakov, 1973,
Limnology and Oceanography,
18, 86–94). The total CO
2 results are lower by 300
μmol kg
−1 in surface waters, and 50
μmol kg
−1 in deep waters, than data reported from the 1969
Atlantis II expedition. While changes in Black Sea hydrography have been documented, these CO
2 system changes are far too large to be accounted for by these processes and are more likely the result of improved technique, rather than geochemical evolution.