GEOTHERMAL GRADIENTS IN NEW ENGLAND HOLOCENE LAKE SEDIMENT

The geothermal gradient in the bottom sediment of nine New England lakes was measured in 1967-68 and corrected for seasonal temperature fluctuations at the sediment/water boundary, warm-rim anomalies, rate of sedimentation, and heat refraction anomalies.

Using a multiple linear regression of the temperature data and a mathematical model to describe the propagation of a seasonal thermal wave in the sediment (Johnson and Likens, 1967), the geothermal gradients were computed and compared to the measured values. The mean annual temperature of the sediment and the seasonal temperature variation on the lake bottom were also computed using the mathematical model.

Analyses of a 12.4-m core from one lake (Mirror Lake, NH) and of sediment sampled near the water-sediment interface in the other eight lakes show the organic composition and water content of the sediment varies less than 10 percent in the steady-state temperature zone. Terrestrial heat flow at the geothermometry sites was estimated using the computed geothermal gradients and the thermal conductivity of the sediment collected near the bottom of Pearl Pond, NH. In most instances, the heat flow values are ± 30% when compared to values measured at bore-hole sites close to the geothermometry sites, or when bore hole and geothermometry sites are in the same rock type (Birch et al., 1968).