FIELD INVESTIGATION OF WINTER THERMODYNAMICS AND HYDRODYNAMICS IN A SMALL KARELIAN LAKE

During late winter (18 March-7 April 1994), temperature and current me asurements were made in Lake Vendyurskoe, Russia, including three surv eys at six cross sections of the lake. Also, the temperature profile e volution was registered with two thermistor chains at two stations (bo ttom depths of 7.6 and 11.5 m) until the time of ice breakup. Temperat ure 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 al most horizontal and evenly spaced vertically, so no conditions for lar ge-scale, density-induced currents existed. The heat flux from sedimen ts to water ranged from 0.6 to 2.0 W m(-2). These values were inversel y 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 b ecame apparent, this flux increased by a factor of two. When solar rad iation increased, convection occurred in the upper layers of the water column. When solar radiation heating became significant at the beginn ing of spring, the average net heat flux at the ice-water interface du ring daytime was 7.7 W m(-2). Weak currents (few mm s(-1)) with a seic he-like character were observed, which most likely resulted from ice-c over oscillations.