Interannual variability of the pH value in the surface layer of the deep-water part of the Black Sea

by

A.B. Polonsky, E.A. Grebneva

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

Е-mail: apolonsky5@mail.ru, lenagrebneva12@gmail.com

DOI: 10.33075/2220-5861-2022-2-12-21

UDC 551.464.6/465.7(262.5)

Abstract:

   According to IPTS archival data for the period from 1957 to 1996, an equidistant time series of the pH value in the surface layer of the deep-water part of the Black Sea has been restored, resolving an intra-annual cycle and and making it possible to refine the characteristics of interannual pH variations, as well as trends of this value. The results of the analysis of the obtained series showed that, due to the statistical structure, it is divided into two twenty-year time periods, different in quality of primary data and the sign of long-term pH trends.  The first time period covers the period from 1957 to 1976, and the second – from 1977 to 1996. The first time period is characterized by a positive (although insignificant) trend of pH changes (0.006 pH units / 10 years), the second by a negative linear trend (-0.03 pH units/ 10 years).  The standard deviation of the first time series is 0.06 pH units, the second is 0.07. At the same time, the difference in pH variances for these two periods is statistically insignificant (at a confidence level of 95%). After adding uncorrelated white noise to the interpolated pH values and removing linear trends, a stationary time series was obtained. As a result of spectral analysis of the pH value from 1957 to 1996, a significant (at the level of 80% confidence interval) quasi-periodic component with a period of 10 years was identified in its time course. The obtained quantitative estimates significantly refine the previously published results of the analysis of the time course of the pH value in the surface layer of the deep-water part of the Black Sea in the second half of the 20th century.

Keywords: Black Sea, deep water, surface layer, pH value, stationary time series, annual cycle, interpolation, interannual variability.

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