Characteristics and seasonal variations of pH in the southern shelf of the Caspian sea

ABSTRACT

This paper presents distribution and seasonal variations of pH over the southern Caspian Shelf adjacent to Iran. The pH data were collected down to 200m depth in two areas in east [off Babolsar in Mazandaran] and west [off Kiyashahr in Gilan] of the Caspian Sea southern coast. The data were collected using a pH sensor of a CTD probe in summer 2003 and spring and autumn 2004. In summer, when the surface water temperature was highest and the strongest seasonal thermo cline existed, the maximum value for pH was observed. In this season, pH had a value of 8.35-8.4 at the water surface. This amount reduced to 8.2 at 80-m level and even deeper waters. In autumn, the pH was less than summer and was mainly 8.25 at the water surface outside of the shelf and 8.3-8.35 in the shelf and it gradually reduced by decreasing the depth. In early spring, during the formation process of new seasonal thermo cline, low temperature and maximum local river inflow, pH at the water surface was mainly 8.25 and reduced to 8.2 at 30-m level. The results showed that seasonal variations of pH in the southern Caspian Shelf and the coastal waters adjacent to Iran is a function of seasonal variations in water temperature, characteristics of thermo cline, local rivers chemical characteristics and discharges, and production or degradation processes