Astronomical Forcings Shaped Timing of Glacial Cycles during Early Pleistocene, Study Says
An artist’s impression of how astronomical forces affect the Earth’s motion, climate, and ice sheets. Image credit: NAOJ.
“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 in the amplitude of variation of the spin axis orientation and the orbit of the Earth;
(ii) the timing of deglaciation is determined mainly by the position of the summer solstice on its orbit, which is at perihelion, not only by the effect of periodical change of the tilt of the Earth’s axis;
(iii) the timing of the change in the spin axis orientation and the position of the summer solstice on its orbit determines the duration of the interglacial period.”
“As geological evidence from older times comes to light, it is becoming clear that the Earth had a different climatic regime than it does today,” said Dr. Takashi Ito, a researcher at the National Astronomical Observatory of Japan.
“We must have a different understanding of the role of astronomical forcing in the distant past.”
“The numerical simulations performed in this study not only reproduce the Pleistocene glacial-interglacial cycle well, but also successfully explain the complex effects of how astronomical forcing drove the cycle at that time.”
“We can regard this work as a starting point for the study of glacial cycles beyond the present day Earth.”
Source: Sci News