Geothermal studies of the Outokumpu Deep Drill Hole, Finland: Vertical variation in heat flow and palaeoclimatic implications

► We present high-resolution geothermal results in a 2.5 km deep hole in Outokumpu in the Fennoscandian shield. ► Heat flow increases significantly from 28-32 mW m−2 in the uppermost 1000 m and achieves 40-45 mW m−2 at depths >2000 m. ► The vertical variation is attributed to a palaeoclimatic effect during the last 100 kyr B.P. ► The average ground surface temperature was −3 to −4 °C during the Weichselian (about 90 kyr - 9 kyr B.P.). ► Heat transfer is dominantly conductive and advective heat transfer was not observed in the formation.