Thermal properties of bottom sediments of Lake Baikal (according to data on temperature field recovery in underwater boreholes)

Thermal conductivity of rocks is a key parameter in heat now determination. Thermal conductivity of the Baikal bottom sediments in cores from first un derwater boreholes (BDP-93 and BDP-96) was measured by a needle probe and a thermal-conductivity comparator, and the two methods showed a difference o f up to 30-50% in the values of both thermal conductivity and heat flow. In this study we used a new method implying evaluation of thermal conductivit y of sediments through interpretation (inversion modeling) of temperature f ield recovery in boreholes after the cessation of drilling. The modeling pa rameters are steady-state temperature and thermal conductivity of bottom se diments at a depth of temperature monitoring. As a result, it was concluded that the needle probe measurements are reliable, and the thermal-conductiv ity comparator cannot be used to study unconsolidated sediments with water contents above 40%. The obtained estimates of steady-state temperature and geothermal gradient confirmed that the heat now is relatively low (about 50 mW/m(2)) in the Bugul'deika saddle (BDP-93) and high (78 mW/m(2), an updat ed value) in the axial part of the Akademichesky Ridge (BDP-96). The new me thod allowed us to estimate, for the first time, the thermal-diffusivity co efficient and the specific heat capacity of the Baikal sediments. Thus, the numerical analysis of temperature monitoring data permits estimation of al l geothermal parameters of sediments.