Alkalinity of the anoxic waters in the Western Black Sea

Measurements of total alkalinity and nutrients were made on samples from discrete depths, aboard the R/V Knorr, May 2001 in the Black Sea. Determination of macronutrient concentrations permits inclusion of these minor bases in alkalinity calculations and thus improved determination of the carbonate system. The permanent pycnocline maintains vertical separation of the oxic, suboxic and anoxic waters of the Black Sea. Results show an apparent excess in alkalinity and/or deficit in hydrogen sulfide from the stoichiometric ratio predicted from the sequential oxidation of Redfield organic matter by sulfate in the anoxic waters near the center of the western gyre. The lateral ventilation of the main pycnocline by Bosporus plume waters is responsible for consuming or removing sulfide from the anoxic zone. The removal of sulfide via intrusion of oxygen-enriched waters and generation of alkalinity and total inorganic carbon dioxide via dissolution of calcium carbonate results in differing stoichiometry between the upper and lower anoxic zones in the center of the western gyre. Changes in the distribution of nutrients and hydrogen sulfide are due to the oxidation of particulate organic matter apparently due to increased productivity in surface waters.