Early Pleistocene East Antarctic temperature in phase with local insolation

Pleistocene glacial–interglacial cycles are hypothesized to be modulated by Earth’s orbital parameters through their influence on the Northern Hemisphere summer insolation. Changes in obliquity—Earth’s axial tilt—can explain the 41,000-year glacial cycles in the Early Pleistocene. However, the absence of 19,000- and 23,000-year frequencies corresponding to Earth’s precession of the rotation axis from those cycles remains enigmatic. Here we investigate how these orbital forcings may have changed by developing an insolation proxy based on the oxygen-to-nitrogen ratio of gases trapped in ice core samples collected from the Allan Hills Blue Ice Area in East Antarctica. We find that East Antarctic temperature was positively correlated with local, Southern Hemisphere summer insolation in the Early Pleistocene, while this correlation became negative in the late Pleistocene, with only the latter being consistent with the previous findings that Northern Hemisphere insolation paced Antarctic climate. If Early Pleistocene ice volume and local Antarctic temperature co-varied, our result supports the hypothesis that attributes the absence of precession in the 41,000-year glacial cycles to cancellation of precession frequencies in hemispheric ice volume changes that are responding to local insolation, suggesting a more dynamic East Antarctic Ice Sheet in the Early Pleistocene than in the past 800,000 years.