The large lakes of arctic, subarctic and taiga zones with area of more than 500 km² were selected for the analysis of formation and functioning of the lakes' ecosystems in relation to geographical latitude. The total of 30 lakes was considered: 1 in the arctic zone, 9 in subarctic and 20 in taiga. Although the level of limnolo-gic data significantly differed from lake to lake, the dependence was quite clearly educed between the structure of a lake ecosystem and factors coming from the latitude (climate, air and water temperatures) as well as geological peculiarities of catchment areas and morphometry of lake beds. Hydrochemical and hydrobiological conditions of lakes are closely connected with these factors, though the anthropogenic action that is more frequent in taiga may disturb the natural indices of lakes' condition, which was also taken into consideration in its portrayal.

Interocean circulation compensates the losses of heat and fresh water from the surface of Atlantic Ocean. Due to the difference in densities of Northern parts of the Pacific and Atlantic oceans, the steric level differential of about 60 cm is formed, where its main reason is the salinity difference. The estimations of meridional heat and fresh water transfer in the oceans are analyzed, considering water exchange in Bering Strait and seas of Indonesia. The different ways of heat and fresh water return to the Atlantic Ocean in the system of interocean circulation are shown: heat transfer is determined by the flow through seas of Indonesia, Southern part of the Indian Ocean and Agulhas Current, and fresh water comes from the Arctic Ocean and Antarctic transitional waters of low salinity. The possible reasons of changes in meridional circulation rate due to changes of hydrologic balance of the Northern Atlantic are also explored.