What was the surface temperature in central Antarctica during the last glacial maximum?

The temperature increase at Vostok (Antarctica) from the last glacial maximum to the present warm period is about 8°C based on the deuterium isotope profile. The bore hole temperature (temperature profile in the ice sheet) indicates that the temperature difference may have been much larger, about 15°C. The temperature dependent gas occlusion process is the key to evaluate the two scenarios. Atmospheric air penetrates the porous firn layer of the ice sheet and gets trapped at the firn ice boundary. Consequently the air is younger than the surrounding ice when it gets enclosed in bubbles. This age difference (Δage) between ice and enclosed gas is temperature and accumulation rate dependent. Therefore it is possible to estimate paleotemperatures from a known Δage. We use the linkage between chronologies of CH4 and water isotopes from Byrd station and Vostok to obtain an experimental Δage for Vostok. This experimental Δage is then compared to modeled Δage for the two temperature scenarios. Our results indicate that the temperature reconstruction deduced from the water isotopic composition is the more probable one.