Significant features of the calendar of the late Pleistocene glacial cycles

Comparison of the δD deuterium record in the ice cores at the Antarctic Vostok and Dome C stations with the δ18 oxygen isotope in bottom oceanic sediments has elucidated the boundaries of glacial cycles in the late Pleistocene and revealed their inner symmetry: the longer the cycles, the more distant they were from the interglacial that occurred approximately 400 kyr ago. The symmetry is also manifested in the reversal of the sawtooth sequence of the cycles in that period. Wavelet analysis shows that symmetry was induced by amplitude modulation of climate oscillations on the precession and obliquity time scales and by frequency modulation on the scales of the eccentricity of the Earth’s orbital motion around the Sun.