At https://phys.org/news/2023-08-late-pleistocene-glaciations-terminated-earth.html … the headline here is that new research finds Late Pleistocene glaciations were terminated by earth’s axis tilt rather than orbital eccentricity. They are not, of course, thinking in terms of pole shift. The most simplistic mechanism for the Ice Age. Instead, it is a variation on Milankovitch. They are questioning the idea of 100,000 year timescales for glaciations. Eccentricity is in fact the weakest of the Milankovitch effects. Obliquity refers to the varying tilt of the planet, somewhere between 22.1 and 24.5 degrees, over 41,000 years. This is apparently the stronger effect. On top of that we have precession. In simple terms this is the direction earth’s axis is pointed – which can make the seasons more extreme on one hemisphere than the other.
Eccentricity has been the feature favoured to drive glacial cycles – even though it is a weak effect and may actually have something to do with the sun’s orbit around its barycentre. Recent research has suggested that obliquity or precession cycles are the driver, at 41,000 and 23,000 year intervals. The new research suggests it was precession that seems to affect glacial cycles the most. Note – they only looked at the three aspects of Milankovitch. No other process was used in their computer simulation. Catastrophism, for example, was completely ignored, and the sun’s barycentre. The idea of pole shift would have been a surprising addition as it is definitely forbidden territory. That is a bit surprising in view of what is being learnt about the sun and the earth in regards electro magnetic processes. A movement generated at the earth’s dipole is theoretically possible as it doesn’t require a large cosmic body to be involved. The energy is in the plasma generated by the Sun. However, the process by which they arrived at their conclusion is interesting, in several ways. For example, the use of oxygen isotopes in foraminifera shells. These are found in sediment cores. Previously, they have been used to support the 100,000 year cycle. In addition, late Pleistocene data shows a rapid divergence in oxygen ratios. This indicates a change in deep sea temperaratures – as a result of variation in ice volume. On the other hand, may it have something to do with Dansgaard-Oerschger warming events, a little understood feature of the Late Pleistocene.
Also, dating orbital change they relied upon speleotherm records from China. Speleotherms are mineral deposits in caves, such as the slow accumulation of flowstone and the calcite accumulation on stalactites. These produced a record going back 640,000 years ago, we are assured. What is especially interesting is that the researchers identified 9 glacial termination events – 3 being partial terminations. Hence, 6 were full terminations [glacial to interglacial conditions]. See https://doi.org/10.1038/s41561-023-01235-x …