Institute of Natural and Technical Systems, RF, Sevastopol, Lenin St., 28
The paper analyzes the interannual variability of the pH value in the surface layer of the deep-water part of the Black Sea for the period from 1957 to 1996. It is shown that the time series is divided into two different time periods in terms of sign and quality of data: from 1957 to 1976 and from 1977 to 1996. Due to the lower measurement accuracy of the first-time interval, further data from 1977 are used in the work. For the period from 1977 to 1996. an empirical model of the time series was developed and a retrospective forecast is calculated with an assessment of its quality based on the data of field studies carried out from 2019 to 2021. The choice of a time series model was carried out on the basis of an analysis of the structure of seasonal fluctuations. The calculation of the values of the seasonal component show that the amplitude of fluctuations is approximately constant. Therefore, when developing a model, each term of the time series is presented in an additive form. Extrapolation from 1996 to 2021 is calculated on the basis of a simple regression model using the performed series decomposition. Based on the results of the developed empirical model of the long-term change in the pH value, it is obtained that in the interannual pH variations, two quasi-periodic components of variability are distinguished. Their periods are about 6.7 and 2.5 years. The trend of changes in pH values in the surface layer of the deep-water part of the Black Sea is close to the trends observed in other regions of the open parts of the World Ocean. The pH values decreased from 1977 to 2021. with an average rate of about 0.01 units pH/10 years. Expeditionary data obtained in 2019–2021, on the whole, confirm the identified trends and fully correspond to the presented retrospective forecast.
Keywords: Black Sea, deep-water part, surface layer, pH value, time series, additive model, extrapolation.
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