TEMPERATURE LOGS IN DEEP WELLS - A USEFUL TOOL FOR PAST CLIMATIC RECONSTRUCTION

According to the theory of heat conduction in a semi-infinite body, te mperature changes at the surface propagate into the subsurface with th e amplitude attenuation and time delay that increase with depth. Tempe rature changes on the earth's surface, reflecting the past climatic hi story, can thus be evaluated by analysing the curvature they have caus ed in the present temperature-depth distribution. As a rule, temperatu re profiles to depths of 200-300 m record surface temperature trends a ccurately over the last two centuries or so; deeper holes may reveal c limate history farther back but with decreasing resolution. We present several synthetic temperature-depth profiles to demonstrate the expec ted signature of past surface temperature changes in the subsurface, t he analysis of which may help better identify the climate of the past. Examples of extracted climate recollections from holes in North Ameri ca and Europe are discussed. While inconspicuous underground records m ay correspond to the postglacial warming 8-11 kyr ago, reasonably well -documented borehole logging data have confirmed climate excursions in the past millenium, namely the Little Climate Optimum and the Little Ice Age. Traces of recent warming are generally common in many tempera ture records, evidencing the temperature rise by 1-2 K over the past 1 00 years.