Signature of the last ice age in the present subsurface temperatures in the Czech Republic and Slovenia

Abstract

Ground surface temperature (GST) history can be evaluated by analysing the present-day temperature-depth profiles measured in boreholes. Due to the diffusive character of the process, however, the resolution of the method decreases quickly for the more remote events. The reconstructed GST at a given moment in the past is a weighted average of temperature over a certain period of time. The present study shows that because the cold climate of the last (Weichselian) glacial prevailed in the period of 75–10 ka, there is a chance to obtain its mean GST, despite the large averaging intervals, from temperature profiles measured in deep boreholes. This fact is demonstrated on the GST inversions of carefully selected profiles, three from the Czech Republic and two from Slovenia, the depth of which ranges between 1.5 and 2.4 km. They yield GST histories with a minimum between 19 and 10 ka followed by a warming of 6–15 K. In order to suppress the nonclimatic noise and to extract the common signal, the joint inversions were carried out for the Czech and the Slovenian boreholes, respectively. The Czech data show the minimum at 17 ka and the warming of 8 K. The Slovenian data have the minimum at 16 ka and the warming amounts to 7 K. These results agree well with information extracted earlier from the German KTB super deep borehole, where the inversion of the temperature log indicated 10 K warming since the glacial minimum, and represent an independent estimate of the difference between glacial and interglacial conditions typical for the region of Central Europe.