The spatiotemporal variability of pH in waters of the Black Sea

Based on archival data of the Institute of Natural and Technical Systems for the period from 1956 to 2010, the large-scale structure, seasonal variability, and long-term trends of pH variations in the upper 150-m layer of the deep-water part of the Black Sea were analyzed. The spatial climatic inhomogeneities of pH in the surface layer of the open part of the Black Sea are about 0.06 pH units; the magnitude of the average seasonal cycle is 0.05 pH units. In the deep-water part of the sea, low values of pH are observed in the vicinity of the centers of cyclonic gyres, where more acidic waters move upward. A long-term increase in the acidity of waters of the surface layer is observed. Thetrend of pH in this layer is generally conditioned by the increase in the CO2 content in the lower troposphere and absorption of part of the excess CO2 by sea water. The increase in the acidity manifests itself in the decrease in pH (at a level of –0.06 pH units per 50 years) in waters of the surface layer. This is close to the estimations for other regions of the World Ocean. However, the intermediate waters are characterized by a negative pH trend, the absolute value of which exceeds more than fivefold the pH trend on the surface. A likely reason for the intense decrease in pH here is the intensification long-term vertical circulation in the intermediate layer of the Black Sea waters, resulting in the ascension of more acidic waters with a typical velocity of ~1 m per year. This can lead to more intense acidification of surface waters in the sea over the next 10 years.

Polonsky A. B. & Grebneva E. A., 2019. The spatiotemporal variability of pH in waters of the Black Sea. Doklady Earth Sciences 486 (2): 669–674. Article.

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