ИСТИНА

Many stratified salt lakes have appeared on the coast of the White Sea as a result of the postglacial isostatic uplift and subsequent isolation of marine bays, at different stages of isolation. On their evolutionary way to the final freshwater body they pass through the meromictic stage. More than twenty meromictic lakes have been identified on the coast of the Kandalaksha Gulf of the White Sea. They differ in size, frequency of sea water intrusions and salinity, but, nevertheless, they have common features. A typical vertical structure consists of five layers: 1) the zone of wind mixing (usually by the depth of 1 m), the salinity in it is less than in the underlying water; 2) halocline (pycnocline); 3) hypolimnion with higher salinity, its upper layer is oxygenated, 4) chemocline (redox zone) - a transition zone from aerobic to anaerobic conditions; 5) anaerobic monimolimnion with high concentration of hydrogen sulfide. This structure is maintained throughout the year, although the thickness of the layers can vary from year to year. In winter, the reservoirs are covered with ice, so there is no wind mixing, however, the surface layer is still characterized by a decreased salinity due to the accumulation of fresh runoff under ice. The chemocline position is annually determined in late fall or early winter, and depends on the amount and thermohaline characteristics of surface sea water that enters the lake. Late January, or in February ice barrier is formed, which prevents or minimizes sea water intrusions. The circulation ends when ice barrier blocks the way of sea water, resulted in stagnation, and formation of the density and chemical stratification. Seasonal ice isolation is one of the most important features of coastal stratified water bodies, which determines their hydrological difference from scoop-type inlets, also numerous in the White Sea. The last ones have not five, but a three-layer structure as they lack a surface diluted layer and associated pycnocline.