Ground surface temperature histories reconstructed from boreholes in Poland: Implications for spatial variability

Abstract

We present results from inversions for ground surface temperature histories (GSTH), reconstructed from two deep boreholes in Poland. One data set comes from the Udryn borehole, located in northeastern Poland. It implies temperatures during the last glacial maximum (LGM) near -10°C, some 18 K lower than today. Since Udryn is located in a low heat flow region (40 mW m-2), a thick permafrost layer could develop. The associated latent heat effect is important and was considered in the inversions.The second data set originates from Czeszewo which lies in western Poland, about 400 km from Udryn. Here, heat flow is considerably higher (≈90 mW m-2). This prevents the formation of a thick permafrost layer in spite of the high porosities. First results from GSTH inversions suggest about 10 K lower temperatures at the LGM than today. This is considerably less than in Udryn and confirmed by recently published results of the 2.9 km deep temperature log in the Torun borehole (130 km NE of Czeszewo), which shows heat flow values around 60 mW m-2.We discuss possible reasons for this large difference of the temperatures during the LGM within a few 100 km. The most important seems to be the different position with respect to the time-dependent rim of the Eurasian ice sheet. © Springer Science + Business Media B.V. 2010.