Evolution of Anoxic Conditions in Black Sea During Holocene: Water

The condition for oxygen depletion in the Black Sea was established 9,000 years ago, when significant influx of Mediterranean water through the Bosporus began to develop a density stratification in the basin. If a logarithmically decreasing rate of oxygen consumption is assumed, a "decay" constant for the oxygen reservoir of 3.8 10-4/year can be calculated, corresponding to a half life of 1,800 years. With the aid of this constant and curves of the distribution of volume and area versus depth, the rise of the O2-H2S interface and the growth of the anoxic water in terms of occupied volume and bottom area can be calculated. In agreement with observations, the calculations show that anoxic conditions began in the deepest part of the basin about 7,300 years ago and that the interface has continued to rise slowly in the recent past.