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Identification of the oxic anoxic interface by isopycnal surfaces in the black sea

Tuğrul, Süleyman
Oğuz, Temel
The analysis of hydrochemical data collected in the Black Sea since 1987 shows that the upper boundary of the oxic/anoxic interface zone coincides with the nitrate maximum at the depths of sigma(t) congruent-to 15.40 +/- 0.10 isopycnal surface. Its lower boundary corresponds to the phosphate maximum depth at sigma(t) congruent-to 16.20 +/- 0.05 isopycnal surface, independent of the geographical location and season. In the absence of the continuous pump cast measurement system, and when the oxygen and sulphide concentrations are too low to be measured with sufficient precision within the interface zone, such features of the oxygen-nitrate and H2S-phosphate correlations at specific density levels provide a direct and practical way to identify the oxic/anoxic interface zone. This, in turn, allows for a more precise and systematic water sampling for studying the complex biogeochemistry of the layer.