NATURE, cilt.359, ss.137-139, 1992 (SCI İndekslerine Giren Dergi)
DURING the past two decades, catastrophic changes have occurred in the Black Sea ecosystem: the influx of pollution from the major rivers has caused intense eutrophication at the northwest coastal margin1, and fish stocks have collapsed throughout the sea2. The hydrochemical details of these events are still poorly understood3-7, and a way needs to be found to distinguish long-term variations from short-term natural fluctuations3,4 if future management of the Black Sea ecosystem is to be successful. We show here that a coherent description may be achieved by analysing the hydrochemical data as a function of water density rather than depth. Our findings suggest that, contrary to the suggestion of Murray et al.3, the upper boundary of the low-lying anoxic waters has remained stationary since 1969, whereas the intermediate suboxic zone has enlarged, reducing the overall depth of the oxygenated upper waters by approximately 20 m. Moreover, a long-term increase in the nitrate concentration and a concomitant decrease in the silicate and ammonia concentrations in this upper layer are indicative of the considerable changes taking place in the biochemical regime of the Black Sea.