The features of the correlation between the pH values and the dissolved oxygen at the Chistaya Balka test area in the Northern Caspian Sea

Abnormally high pH values (up to 9 NBS units and over) were registered by different expeditions at the seaward edge of the Volga River delta. Within the report, the relationship of the pH values, the dissolved oxygen content, and the water temperature are considered using the equations of the thermodynamic theory of carbonate equilibrium. It is shown that the changes of the pH values are nonlinear relative to the content of oxygen. The nonlinearity is most pronounced at high values of the water saturation with oxygen (over 110–120%). A pH value over 9 may be reached in well heated waters at a dissolved oxygen content of 8–9 ml/l. The oxygen content as such is of course high but not excessive and might be caused by the high intensity of the production processes in the waters.