On thermohaline structure and circulation of the Western Large Aral Sea from 2009 to 2011: Observations and modeling

- Vertical thermohaline structure of the Aral Sea is essentially 3-layered.
- Basin-scale surface circulation of the lake is anti-cyclonic under dominant winds.
- Anti-cyclonic character of the gyre is due to the “asymmetric” bathymetry.
- Bottom circulation of the lake is determined by stratification of water column.

The shrinkage of the Aral Sea in the second half of the past century has significantly affected the hydrophysical regime of the lake. The objective of this paper is to report on a hydrological structure and circulation of the today's Aral Sea based on both direct field observations and modeling results. We focus on the results of three field surveys to the Aral Sea which took place in the period from 2009 to 2011. In addition, series of numerical experiments using Princeton Ocean Model adapted to the Aral Sea was undertaken to investigate the contributions from bathymetry and water stratification in the formation of the basin scale circulation. The hydrological structure of the Aral's western basin in autumn season exhibited a three-layered pattern with two local salinity maxima, separated by a fresher intermediate layer. According to direct observations, water circulation in the surface layer has anti-cyclonic character, while circulation in the bottom layer has cyclonic sign under the predominant northerly winds. The simulation experiments demonstrated clearly that the main cause of the anti-cyclonic circulation in the surface layer of the lake is the “asymmetric” bathymetry with broad shallow area along the eastern coast and relatively steep and deep western slope. However, strong stratification is a necessary condition for the formation of the cyclonic circulation gyre in the bottom layer.