Abstract:
Large temperature variations on millennial time scales in Greenland characterised the last ice age. Abrupt warmings, known as Dansgaard–Oeschger (DO) events, can be traced in the δ18Oice record of Greenland ice cores. However, it has been shown that δ18Oice is not a direct temperature proxy. Measurements of the isotopic composition of gases trapped in the ice can be used to calibrate the paleothermometer. Here we present a continuous temperature record based on high resolution δ15N measurements and firn model studies. It covers a sequence of 9 DO events (9–17) during the time period from 38 to 64 kyr BP for which temperature changes of 8 to 15 °C were estimated. The difference between the modern and the glacial δ18Oice–T relationship can be explained by a combination of source temperature changes and changes in the annual distribution of precipitation. A detailed comparison of the temperature evolution with reconstructions of the atmospheric methane (CH4) concentration shows that CH4 rises lag temperature increases at the onset of DO events by 25 to 70 yr within data resolution. The strong correlation between Greenland temperature and CH4 on millennial and submillennial time scales suggests that variations on these time scales were probably of hemispheric extent.
