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.

更新世冰期-间冰期循环被假设为通过地球轨道参数对北半球夏季日照的影响来调节。倾角的变化——地球的轴向倾斜——可以解释早更新世 41,000 年的冰川周期。然而，与这些周期中地球自转轴进动相对应的 19,000 年和 23,000 年频率的缺失仍然是个谜。在这里，我们根据从南极洲东部艾伦山蓝冰区收集的冰芯样本中捕获的气体的氧氮比，开发了一个日照代理来研究这些轨道强迫可能如何变化。我们发现南极东部温度与早更新世南半球局部夏季日照呈正相关，而这种相关性在更新世晚期变为负值，只有后者与之前关于北半球日照影响南极气候的发现一致。如果早更新世冰量和南极当地温度共同变化，我们的结果支持这样的假设，即 41,000 年冰川周期中没有进动归因于抵消了响应当地日照的半球冰量变化中的进动频率，这表明更新世早期的南极东部冰盖比过去 80 万年更具活力。