Field investigation of winter thermo- and hydrodynamics in a small Karelian lake

During late winter (18 March-7 April 1994), temperature and current measurements were made in Lake Vendyurskoe, Russia, including three surveys at six cross sections of the lake. Also, the temperature profile evolution was registered with two thermistor chains at two stations (bottom depths of 7.6 and 11.5 m) until the time of ice breakup. Temperature gradients were measured just below the ice cover and in the upper 10-cm layer of the bottom sediments. The isotherms were found to be almost horizontal and evenly spaced vertically, so no conditions for large-scale, density-induced currents existed. The heat flux from sediments to water ranged from 0.6 to 2.0 W m(-2). These values were inversely related to the depth. The heat Aux from water to ice ranged from 0.7 to 1.2 W m(-2). When water heating from solar radiation penetration became apparent, this flux increased by a factor of two. When solar radiation increased, convection occurred in the upper layers of the water column. When solar radiation heating became significant at the beginning of spring, the average net heat flux at the ice-water interface during daytime was 7.7 W m(-2). Weak currents (few mm s(-1)) with a seiche-like character were observed, which most likely resulted from ice-cover oscillations.