Glacial cycles during the Early Pleistocene epoch 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 is unclear how the 41,000-year glacial cycles during the Early Pleistocene respond to Earth’s astronomical forcings.
“Earth’s orbit around the Sun and its spin axis orientation change slowly over time, due to the pull of gravity from the Sun, the Moon, and other planets,” said University of Tokyo researcher Ayako Abe-Ouchi and colleagues.
“These astronomical forces affect the environment on Earth due to changes in the distribution of sunlight and the contrast between the seasons.”
“In particular, ice sheets are sensitive to these external forces resulting in a cycle between glacial and interglacial periods.”
“The present-day glacial-interglacial cycle has a period of about 100,000 years,” they added.
“However, the glacial cycle in the Early Pleistocene (about 800,000 years ago) switched more rapidly, with a cycle of about 40,000 years.”
“It has been believed that astronomical external forces are responsible for this change, but the details of the mechanism have not been understood.”
“In recent years, it has become possible to investigate in more detail the role of astronomical forces through the refinement of geological data and the development of theoretical research.”
In their new research, the authors employed a three-dimensional ice-sheet model to simulate the glacial cycles at 1.6–1.2 million years before present.
“Our large numerical simulations reproduce well the glacial cycle of 40,000-year of the Early Pleistocene as indicated by the geological record data,” they said.
“From analysis of these simulation results, we identified three facts about the mechanisms by which astronomical forces caused changes in climate in those times:
(i) the glacial cycle is determined by small differences…
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