Some properties of currents and mixing in a shallow ice-covered lake

A study on characteristics of currents and mixing in a shallow ice-covered Russian lake is presented. The current velocity data are separated into four main components, mean velocity, uninodal longitudinal and transverse seiche currents, and "high"-frequency velocity fluctuations, using digital filters. The analysis of components shows that mean currents are most pronounced in early winter and are of the order of 1-10 mm s(-1) All three oscillatory components are, on average, of the same magnitude, 0.1-1 mm s(-1), and about the same as mean currents in midwinter, and do not show any pronounced differences during winter. Mean currents increase during the convective period in late winter up to several millimeters per second. Apart from possible local hydrodynamic instability, induced by salt fluxes at the ice and bottom boundaries, and local turbulence near the boundaries in early winter, the vertical mixing in early winter and midwinter in the lake appears to be determined solely by molecular processes.