‘True polar wander’ may have caused ice age

Posted: November 20, 2018 by oldbrew in Geology, Ice ages, research
Tags:

Ross Ice Shelf, Antarctica


The latest research comes up with a new addition to the list of possible ice age mechanisms.

Earth’s latest ice age may have been caused by changes deep inside the planet, reports ScienceDaily.

Based on evidence from the Pacific Ocean, including the position of the Hawaiian Islands, Rice University geophysicists have determined Earth shifted relative to its spin axis within the past 12 million years, which caused Greenland to move far enough toward the north pole to kick off the ice age that began about 3.2 million years ago.

Their study in the journal Geophysical Research Letters is based on an analysis of fossil signatures from deep ocean sediments, the magnetic signature of oceanic crust and the position of the mantle “hot spot” that created the Hawaiian Islands.

Co-authors Richard Gordon and Daniel Woodworth said the evidence suggests Earth spun steadily for millions of years before shifting relative to its spin axis, an effect geophysicists refer to as “true polar wander.”

“The Hawaiian hot spot was fixed, relative to the spin axis, from about 48 million years ago to about 12 million years ago, but it was fixed at a latitude farther north than we find it today,” said Woodworth, a graduate student in Rice’s Department of Earth, Environmental and Planetary Sciences.

“By comparing the Hawaiian hot spot to the rest of the Earth, we can see that that shift in location was reflected in the rest of the Earth and is superimposed on the motion of tectonic plates. That tells us that the entire Earth moved, relative to the spin axis, which we interpret to be true polar wander.”

By volume, Earth is mostly mantle, a thick layer of solid rock that flows under intense pressure and heat. The mantle is covered by an interlocking puzzle of rocky tectonic plates that ride atop it, bumping and slipping against one another at seismically active boundaries. Hot spots, like the one beneath Hawaii, are plumes of hot solid rock that rise from deep within the mantle.

Gordon, the W.M. Keck Professor of Earth, Environmental and Planetary Science, said the new findings build on two 2017 studies: one from his lab that showed how to use hot spots as a global frame of reference for tracking the movement of tectonic plates and another from Harvard University that first tied true polar wander to the onset of the ice age.

“We’re taking these hot spots as marked trackers of plumes that come from the deep mantle, and we’re using that as our reference frame,” he said. “We think the whole global network of hotspots was fixed, relative to the Earth’s spin axis, for at least 36 million years before this shift.”

Continued here.
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Plain Language Summary

The Earth has shifted relative to its spin axis over the past 12 million years (Ma). This shift, which geoscientists call true polar wander, caused the Earth’s mantle beneath the tropical Pacific to move southward while causing Greenland to move northward. The latter motion may have contributed to the onset of the current ice age, which began ≈3 Ma before present. These conclusions follow our analysis of the history of motion of the Pacific tectonic plate relative to the spin axis, which is preserved in sediments and rocks on the Pacific seafloor. We also infer the motion of the Pacific plate relative to the solid Earth from the plate’s history of motion relative to hot spots, such as Hawaii. Hot spots are sites of voluminous volcanism, thought to lie over rising plumes of hot rock from deep in the Earth’s mantle. As the Pacific plate moves over the Hawaiian plume, it creates a line of extinct volcanoes that record the motion of the plate relative to the plume. Combining this information, we find that Hawaii and other global hot spots were nearly fixed in latitude from 48 to 12 Ma before present, which marks a 36‐Ma‐long time interval preceding the shift.

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018GL080787

Comments
  1. Salvatore Del Prete says:

    Does not explain all the abrupt climatic changes especially during the last 20,000 years.

  2. stpaulchuck says:

    The Earth _may_ do that all on its own due to imbalances in density. However, I posit that the Earth has been hit with some rather large objects from space that upset its rotation and eventually caused such a massive shift. It didn’t have to be just one object. A series in time could do it IMHO.

  3. hunter says:

    Wow that’s a lot to think about. Are they claiming that the crust moves like a loose fruit skin?

  4. Alger says:

    I recommend the book Path of the Pole , written by Charles Hapgood. It goes into detail on this very topic. Originally published in 1958!

  5. hunter says:

    The magnetic pole has always wandered, and even flipped.
    The question is what would that have to do with weather?

  6. hunter says:

    Alger, thank you for the reference. I look forward to reading up on the topic.
    Reading the abstract further, it seems this a fascinating if subtle distinction in plate tectonics.

  7. hunter says:

    oldbrew,
    Thank you for the link.
    It is still a lot to wrap one’s brain around.
    🤪

  8. oldbrew says:

    The twin of true polar wander is apparent polar wander.

    Apparent polar wander (APW) is the perceived movement of the Earth’s paleo-magnetic poles relative to a continent while regarding the continent being studied as fixed in position.[1] It is frequently displayed on the present latitude-longitude map as a path connecting the locations of geomagnetic poles, inferred at distinct times using paleomagnetic techniques.

    In reality, the relative polar movement can be either polar wandering or continental drift (or a combination of both).[2] Data from around the globe are needed in order to isolate or distinguish between the two. Nevertheless, the magnetic poles rarely stray far from the geographic poles of the planet. Therefore, the concept of apparent polar wander is very useful in plate tectonics, since it can retrace the relative motion of continents, as well as the formation and break-up of supercontinents. [bold added]

    https://en.wikipedia.org/wiki/Apparent_polar_wander

  9. oldmanK says:

    It seems that the paper made sure to stick to Wiki’s piece by keeping within the bounds of the Pole shift hypothesis https://en.wikipedia.org/wiki/Pole_shift_hypothesis

    So we are sure of the dogma that has a story of what happened about 800 Million years ago, but cannot figure out what happened in the last 8000 years, in spite of the evidence, ancient history, and archaeology. Recall that Plato was clear about the ‘declination of the heavens’, Herodotus about the sun changing its place of rising and setting, and Mela about the stars changing their paths in the heavens.

    Some science is the most obtuse of religions.

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