Eccentricity Controls the Magnitude and Periodicity of Pleistocene Glacial Cycles

Abstract During the Mid‐Pleistocene Transition (∼1,250–750 ka) glacial cycle amplitude and duration increased, from smaller, ∼40 ka‐period middle Pleistocene ice sheets to larger, ∼100 ka‐period late Pleistocene ice sheets. This transition in glacial period and size has been attributed to some combination of long‐term, monotonic, carbon and climate system forcings and ice sheet feedbacks. The early Pleistocene glacial cycles (2,700‐2,000 ka), however, exhibit a ∼100 ka periodicity that coincides with low‐latitude advances of the Laurentide ice sheet further south than the Last Glacial Maximum, and a synthesis of global climate records reveals that the early Pleistocene glacial cycles imparted a larger impact on the climate system than the middle Pleistocene glacial cycles. The occurrence of large, ∼100 ka duration glacial cycles during the early and late Pleistocene necessitates a periodic forcing. We demonstrate that Earth's 2,400 ka eccentricity cycle, through its modulation of precession, controls the magnitude of ice sheet growth at obliquity minima and grows large ice sheets during the early and late Pleistocene. We then relate ice sheet size to glacial cycle duration by showing that terminations are more likely to occur when ice sheets exceed a size threshold and show that during the early and late Pleistocene variable precession conditions result in either: (a) limited growth, such that a termination cannot occur, extending glacial cycle duration, or (b) the largest growths of the Pleistocene. Therefore, we propose that the magnitude and period of Pleistocene ice ages are paced by long‐period changes in the eccentricity of Earth's orbit.