FY 2000

The suboxic zone of the Black Sea

Murray, J.W., B.-S. Lee, J.L. Bullister, and G.W. Luther

In Environmental Degradation of the Black Sea: Challenges and Remedies, S. Besiktepe, Ü. Ünlüata, and A.S. Bologa (eds.), Kluwer Academic Press, 75–91 (1999)

One of the most fascinating and unexpected discoveries during the US-Turkish Expedition to the Black Sea in 1988 was the detection of a suboxic zone at the oxic-anoxic interface. The suboxic zone was defined as the region where the concentrations of oxygen and sulfide were both extremely low and had no perceptible vertical or horizontal gradients. The suboxic zone is a site of intensive redox cycling of species of sulfur, nitrogen, manganese and iron. Further analysis showed that the features of the vertical profiles occurred on characteristic density surfaces, which means they can be reproducibly sampled. Similar reactions appear to occur in hemipelagic marine sediments but are more difficult to study. In the oxygen minima of the world?s oceans the extent of the redox reactions is less complete. Thus, the Black Sea is a natural laboratory to study these reactions because the complete progression of redox reactions is well resolved on characteristic density surfaces within a suitable depth range for resolution by pump-type sampling. In this paper we review our knowledge of the suboxic zone and present five hypotheses for future study.