Abstract. Sediment temperatures were simulated from the sediment-water interface down to 10 rn for circular lakes with surface areas of 0.2-10 km 2 and maximum lake depths of 4-24 m. The calculations were made using daily weather conditions measured over 19 years (1961)(1962)(1963)(1964)(1965)(1966)(1967)(1968)(1969)(1970)(1971)(1972)(1973)(1974)(1975)(1976)(1977)(1978)(1979) at three geographic locations, representing climate conditions from north to south latitudes in the central United States. A one-dimensional sediment temperature model coupled with a year-round lake water temperature model (MINLAKE96) was used. The models were tested against extensive water temperature and some sediment temperature data. Lake sediment equilibrium temperatures at 10 rn below the water-sediment interface were found almost equal to the annual mean temperature of the overlaying water and hence dependent on the lake temperature regime, which in turn depends on the local climate and a lake's physical characteristics (e.g., surface area As, maximum depth H•oc, and water transparency as measured by Secchi depth). The lake geometry ratio A 0'25//-/ (m -ø'5) gives a good indicationwhether a lake will permanently stratify in summer or not, and that makes a large difference for the sediment temperature regime. Sediment temperatures at 10 rn below the littoral waters of a lake are almost equal to subsurface ground (terrestrial) temperatures, regardless of the type of lake, whereas sediment temperatures at 10 rn below the deepest portion of a stratified lake have a strong linear relationship with the logarithm of the lake geometry ratio. Two generalized 10-m sediment temperature profiles were developed, one for ice-covered lakes and the other for year-round open water lakes. Sediment temperatures at 10 rn below the sediment-water interface at different depths of a lake can be reconstructed from the generalized profiles using Secchi depth, surface area, maximum depth, and annual mean air temperature as input. Sediment temperature at several meters depth (e.g., 10 m) below a lake bed is a useful and necessary initial condition to predict water temperature dynamics in lakes of the temperate zone and hence other water quality parameters whose kinetics are linked to water temperature. In this paper, we address a very similar physical situation: sediment temperatures below lakes. In our discussion, the sediment at the bottom of a lake is analogous to soil below the ground surface, and the water-sediment interface in the lake is analogous to a soil (ground) surface. The heat flux into or out of the lake sediments is assumed to be driven solely by the water temperature at the lake bottom (groundwater flow is ignored in this study). Since lake water temperatures are largely determined by heat exchange with the atmosphere, one can say that, in principle, lake sediment temperatures are also driven by atmospheric inputs. However, the modulation ex-717