Study of Water Mass Change Impacts on Water Salinity and Steric Fluctuations in the Caspian Sea

The water level fluctuation associated with water density changes, known as steric fluctuation, is an essential contribution to total sea-level fluctuations and the principal reason for water circulations in the Caspian Sea. Water salinity is one of the main parameters controlling water density. Aside from regular seasonal changes, as an additive parameter, water salinity could have a long-term cumulative impact on the water density and, therefore, on the steric fluctuations. Water mass variations mainly control water salinity rate; it is particularly confirmed in closed inland water bodies. In the absence of water salinity data, utilizing altimetry-derived water level anomaly, we estimated a time series of salinity variation in the Caspian Sea. According to water density changes, steric fluctuations are estimated for four decades (1981–present). The results show that water salinity variations have changed the seasonal amplitude of steric fluctuations, decreasing from 1981 to 1995 and increasing from 1995 to the present. This change exceeds 0.15 mm, equaling 2% of the total seasonal amplitude, during the study period. Considering the continuation of the lake level drop over the last 25 years, water salinity may experience unprecedented increases, resulting in increasing seasonal amplitude of steric fluctuation, which critical changes could follow in water circulation.