THERMAL REGIME AT THE BASE OF THE LATE PLEISTOCENE ICE SHEETS AS INFERRED FROM BOREHOLE TEMPERATURE DATA

ABSTRACT

The last cycle of the glacial history including the glaciation of the Late Pleistocene (100 to 11 kyr BP) and the modern interglacial (Holocene) is a key period in climate research. Understanding the mechanisms of growth, dynamics and decay of ice sheets (the Laurentide ice sheet in North America and the Scandinavian ice sheet in Europe) provides information to understanding past global climate changes and more reliable predictions of the future climate. The direct source of information on the temperature regime at the base of the glaciers is the borehole temperature data. We analyzed 15 estimates of temperatures at the base of the Laurentide ice sheet and 9 estimates at the base of the Scandinavian ice sheet reconstructed from the borehole temperature data. The average ground surface temperature at the maximum of the last glaciation (LGM, 20 kyr BP) in Canada was -0.4 °C (standard deviation 1.4 °C). This temperature is close to the melting point of ice under the pressure of an ice sheet height less than 1 km. No statistical relationship was found between the ground surface temperatures and the geothermal gradient and height of the ice sheet. At the same time, it was found that the temperature regime at the base of the ice sheet depends on the insolation on its upper surface.
The Scandinavian ice sheet demonstrates a greater variety of temperature regimes. On the eastern and southern margins (the eastern part of the Kola Peninsula, Karelia, Northern Poland), LGM temperatures vary from -10 °C to -18 °C. In the central and western parts LGM temperatures at the base of the ice sheet were from -4 °C to + 2 °C. Low ground surface temperatures indicate the absence of a glacier in these areas, or a limited time of its existence.

Keywords: borehole temperature, paleoclimate, Last Glacial Maximum, the Laurentide ice sheet, the Scandinavian ice sheet