About long-period variability of value pH in the deep-sea part of the Black Sea

A.B. Polonsky, E.A. Grebneva

Institute of Natural and Technical Systems, Russian Federation, Sevastopol, Lenin St., 28

Email: apolonsky5@mail.ru, lenagrebneva12@gmail.com

DOI: 10.33075/2220-5861-2019-1-63-71

UDC 551.464.6/465.4(262.5)           


   Based on the archive data of the Institute of Natural and Technical Systems, large-scale field structure and long-term trends in pH values ​​in the upper 150-meter layer of the deep-water part of the Black Sea are analyzed. Regularly updated data bank IPTS contains 169,646 pH measurements at 29,086 stations from 1923 to 2010. The spatial-temporal distribution of stations is not uniform. The most reliable measurements are given for the northwestern shelf and waters adjacent to the southern coast of Crimea and Bosphorus.

   The amount of data in the database is limited. For further analysis, the work uses data for the period from 1956 to 2010, best assured by observations. Spatial climatic heterogeneity of pH in the surface layer of the open part of the Black Sea is about 0.06 units of pH. In the deep-sea part of the sea, lower pH values are observed in the vicinity of the cyclonic gyres centers, where upwelling of more acidic waters occurs. A long-term increase in the acidity of the water surface layer is observed, the magnitude of which is chiefly due to the increase in carbon dioxide content in the lower troposphere and the absorption of some part of excess of CO2 by seawater. This increase is manifested in a decrease of pH in the waters of the sea surface layer which is about 0,06 units of pH for 50 years which is close to estimates obtained for other World ocean regions. At the same time, in the intermediate water area there is a negative trend in the pH value, which exceeds (in absolute value) the trend on the surface by more than 5 times. The probable reason for the intensive decrease  of pH, in this case, is the long-term intensification of the vertical circulation in the intermediate layer of the Black Sea waters, causing the upwelling of more acidic waters at a speed of about 1 m/year. This can lead to a more intense acidification of the sea surface waters already in the coming 10 years.

Keywords: Hydrogen index pH, Black Sea, deep-sea part, pH trends.

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