Researchers reproduce ice age cycle to reveal the astronomical forces at play

These cosmic forces have a significant impact on Earth's ecosystem, changing how sunlight is distributed and affecting how the seasons contrast. The sensitivity of ice sheets to these outside factors accounts for the cyclical character of glacial and interglacial periods.

Early Pleistocene glacial cycle

Due to astronomical factors, the 40,000-year glacial cycle was shorter during the early Pleistocene epoch. The mechanisms underlying the change are revealed by new geological information and theoretical research, providing important new information on Earth's climate dynamics.

The research team, led by Yasuto Watanabe at the University of Tokyo, employed an updated climate computer model that included cutting-edge astronomical ideas to focus on the early Pleistocene Epoch between 1.6 and 1.2 million years ago.

The scientists successfully recreated the 40,000-year glacial cycle of that epoch using intensive numerical simulations, closely agreeing with geological records.

Researchers have made significant discoveries on the influence of celestial influences on ancient climate by examining simulation results. They discovered that the glacial cycle was controlled by tiny fluctuations in the direction of the Earth's spin axis and orbit.

The position of the summer solstice in Earth's orbit, which coincided with perihelion, also played a significant role in determining when deglaciation began. The length of the interglacial period was also dictated by variations in the orientation of the spin axis and the location of the summer solstice.

A member of the research team facilitating the conversation on astronomical external forces, Takashi Ito from the National Astronomical Observatory of Japan, stressed the significance of taking earlier geological evidence into account to fully comprehend Earth's climatic regime.

The study represents an important turning point since it not only accurately reconstructed the Pleistocene glacial-interglacial cycle but also offered insightful information about the astronomical mechanisms that governed this cycle.

This research paves the way for further study of glacial cycles outside of the current Earth.

Study Abstract: 

Glacial cycles during the early Pleistocene are characterized by a dominant 41,000-year periodicity and amplitudes smaller than those of glacial cycles with ~100,000-year periodicity during the late Pleistocene. However, it remains unclear how the 41,000-year glacial cycles during the early Pleistocene respond to Earth’s astronomical forcings. Here we employ a three-dimensional ice-sheet model to simulate the glacial cycles at ~1.6–1.2 million years before present and analyse the phase angle of precession and obliquity at deglaciations. We show that each deglaciation occurs at every other precession minimum, and when obliquity is large. The lead-lag relationship between precession and obliquity controls the length of interglacial periods, the shape of the glacial cycle, and the glacial ice-sheet geometry. The large amplitudes of obliquity and eccentricity during this period helped to establish robust 41,000-year glacial cycles. This behaviour is explained by the threshold mechanism determined by ice-sheet size and astronomical forcings.