Water Exchange between the Northern and Middle Caspian

Abstract

The Caspian Sea water dynamics on the boundary of its northern and central basins is considered. A high-resolution numerical model (with a grid step of ~2 km) has been used to reproduce the mesoscale structure of currents. The results of two experiments are presented: a realistic reconstruction of the sea circulation in 2003 and an idealized one with an artificial forcing. The realistic calculation considers the water exchange between the two basins, which occurs primarily due to coastal jet currents near Tyub-Karagan Peninsula in the east and near the Agrakhan Peninsula in the west. The formation and evolution of these currents under various synoptic situations are analyzed, and their flow rates are quantitatively estimated. The effect of contrasting water intrusions caused by these currents on the salinity field in both basins with highly different haline regimes is estimated. In particular, the western current (WC) is shown to increase the sea surface salinity (SSS) in the Northern Caspian and decrease its value in the Middle Caspian by almost 1–2 psu/year. The water exchange in the east is asymmetric: the northern current increases salinity in the northern basin by 2–3 psu/year, while the southern current decreases the average SSS in the central basin by only around 0.5 psu/year; in this case, the southern current occurs stably only in June and July. The idealized experiment simulates the Caspian water dynamics for winds of various points: from 0° to 350° with a step of 10°. The flow rates of both western and eastern currents have a sinusoidal dependence on the wind direction: their maxima are reached with winds of 40° and 220° points for the WC and with 120° and 300° points for the eastern current (EC). This study also analyzes the establishment of quasi-steady-state sea circulation at a constant wind.