Magnetic field excursion about 41,000-42,000 years ago

[Jarvis323]

A global environmental crisis 42,000 years ago

Do terrestrial geomagnetic field reversals have an effect on Earth's climate? Cooper et al. created a precisely dated radiocarbon record around the time of the Laschamps geomagnetic reversal about 41,000 years ago from the rings of New Zealand swamp kauri trees. This record reveals a substantial increase in the carbon-14 content of the atmosphere culminating during the period of weakening magnetic field strength preceding the polarity switch. The authors modeled the consequences of this event and concluded that the geomagnetic field minimum caused substantial changes in atmospheric ozone concentration that drove synchronous global climate and environmental shifts.

https://science.sciencemag.org/content/371/6531/811

 

[anorlunda]

They are getting praise for high quality data.

https://www.npr.org/2021/02/18/9690...n-the-Earth's-magnetic-field-last-flipped-out
Other researchers say they're really struck by the fact that the scientists were able to construct such a detailed record of the timing of magnetic changes by looking at these trees.

"That high-resolution temporal record is, I think, pretty impressive," says http://geoscience.wisc.edu/geoscience/people/faculty/brad-singer/, a geologist at the University of Wisconsin-Madison who studies the history of the Earth's magnetic field but was not part of the research team. "This is only a small number of specimens that they measured, but the results look fairly reproducible in the different trees, and I think that's a pretty impressive set of data."

 

[Jarvis323]

There is some confusion about it being a pole reversal in the media. Apparently the poles did flip, but the reversal didn't last long enough to be considered a pole reversal, and instead is considered and excursion. The last known pole reversal was about 780,000 years ago.

 

[anorlunda]

There is some confusion about it being a pole reversal in the media. Apparently the poles did flip, but the reversal didn't last long enough to be considered a pole reversal, and instead is considered and excursion. The last known pole reversal was about 780,000 years ago.

That sounds like a meaningless distinction as far as the living beings of the time were concerned.

 

[Genava]

Archaeologists are already pointing out large over interpretation on their argument that this reversal could have caused Neanderthal extinction. On the climate modelling side, their use of SOCOL-MPIOM is interesting. But it is worrying they found such big effect from increasing Brewer-Dobson Circulation.

 

[Jarvis323]

The migration patterns are interesting in light of what we know about the magnetic excursion.

https://en.wikipedia.org/wiki/File:Early_migrations_mercator.svg

Also, a little later (about 39,300 y.o.) there was a major volcanic eruption in Italy as well.
https://en.wikipedia.org/wiki/Campanian_Ignimbrite_eruption.

 

[Jarvis323]

That sounds like a meaningless distinction as far as the living beings of the time were concerned.

The distinction can be a real source of confusion, because it's not the 'assumed to be long stable periods' after the poles have flipped which we should expect to be solely associated with the effects on climate and ecosystems. It's the effects from the flipping process (when the field is unstable and diminished) that are likely the most important, and perhaps to some extent also the continued disorientation as wildlife tries to adapt to the changes. Yet you will find a whole lot of information discussing reversals while ignoring completely excursions (even though they are technically reversals). And in some instances you find arguments suggesting that excursions should be less worrisome as compared to reversals, like in this unsourced claim on Wikipedia.

However, it is likely that nothing serious would occur, as the human species has certainly lived through at least one such event; Homo erectus and possibly Homo heidelbergensis lived through the Brunhes–Matuyama reversal (~780,000 YA) with no known ill effect, and excursions are shorter-lived and do not result in permanent changes to the magnetic field.

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

I would think that more abrupt and chaotic changes would be more dangerous? And we are supposed to know if an ill effect occurred to an archaic human species that we have only a single jawbone from to analyze? And another that we have only a handful of bones and bone fragments of?

If you do a google search on pole reversals, you currently mostly find dumbed down and misleading information that was prepared for the general public to dispel fears that the world was going to end in 2012 by a pole reversal that people thought was predicted by the Mayans.

There is apparently a lot of unknowns about excursions.

[2] Earth's magnetic field varies on a wide range of timescales from micropulsations (<1 s to minutes) to superchrons (>10 Myr). Geomagnetic excursions occur on timescales of a few thousand years, and therefore represent a small part of the spectrum of field behavior. Nevertheless, excursions are one of the less well‐understood aspects of field behavior. An excursion is usually defined as a deviation of the virtual geomagnetic pole (VGP) by more than 40–45° from the geographic pole [Merrill and McFadden, 1994] or as a deviation of VGPs away from the normal range of geomagnetic secular variation [Vandamme, 1994]. Many questions remain about the frequency of excursions (are they rare or common?), their geographic extent (are they global or regional features?), and the type of field behavior they represent (are they dominantly dipolar or non‐dipolar, are they related to geomagnetic secular variation or are they aborted polarity reversals, etc.?). Despite the large literature on excursions, a repeated problem is that anomalous data have been emphasized at the expense of less interesting but more robust data, and, combined with poor chronological constraints, “excursion” records are commonly used to estimate the age of a sedimentary sequence. This has led to a “reinforcement syndrome” [Thompson and Berglund, 1976] that complicates geomagnetic excursion research. Such problems have also wreaked widespread chronostratigraphic havoc in Quaternary research. After over four decades of geomagnetic excursion research, much is known, but much remains unknown. I give a perspective below on these “knowns” and “unknowns”, and suggest further research to address key remaining questions. Any discussion of “knowns” in relation to excursions rapidly strays into “unknowns”. I have tried to retain clarity in such situations.

https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.380.4937&rep=rep1&type=pdf

Besides the Laschamps excursion, there have been many other excursions in the form of 'not long lasting enough pole reversals to be considered pole reversals' (lasting something like 5-10k years).

The distinction between geomagnetic excursions and reversals

Summary

Two recent studies of the geomagnetic field in the last 1Myr have found 14 excursions, large changes in direction lasting 5–10kyr each, six of which are established as global phenomena by correlation between different sites. The older picture of the geomagnetic field enjoying long periods of stable polarity may not therefore be correct; instead, the field appears to suffer many dramatic changes in direction and concomitant reduction in intensity for 10–20 per cent of the time. During excursions the field may reverse in the liquid outer core, which has timescales of 500yr or less, but not in the solid inner core, where the field must change by diffusion with a timescale of 3kyr. This timescale is consistent with the remarkably uniform duration of well-dated excursions. The disparity of dynamical timescales between the inner and outer cores, a factor of 10, is consistent with the 10 excursions between full reversals.

https://academic.oup.com/gji/article/137/1/F1/701015

 

[Baluncore]

Yet you will find a whole lot of information discussing reversals while ignoring completely excursions (even though they are technically reversals).

The reason for the discussion is important. Without some hypothesis to support the argument that the magnetic field has an effect on Earth's climate there is little point in differentiating between reductions, excursions or reversals. Is it the polarity or the strength that is important? What is the hypothesis being tested?

The migration patterns in post #6 are so general that it simply shows a pool of old data from Africa, that becomes available as the ice retreated later towards the pole. The argument that any of those migrations resulted from magnetic instability, is simply not present. Still, it is a bright and colourful picture that conforms to the “Out of Africa” paradigm.

 

[Jarvis323]

The reason for the discussion is important. Without some hypothesis to support the argument that the magnetic field has an effect on Earth's climate there is little point in differentiating between reductions, excursions or reversals. Is it the polarity or the strength that is important? What is the hypothesis being tested?

I don't quite follow.

Can you give an example where excursions are distinguished from reversals for the purpose of testing the hypothesis that polarity alone might affect climate?

And in that case, what would be the motivation to not include polarity changes lasting less than say 15,000 years (excursions)? The argument would be that 15,000 years is not long enough for a hypothesized polarity based climate change to occur?

It's like the climate version of the 5 second rule?

https://en.m.wikipedia.org/wiki/Five-second_rule

 

[Baluncore]

Can you give an example where excursions are distinguished from reversals for the purpose of testing the hypothesis that polarity alone might affect climate?

You need to do your own research. What hypothesis are you testing?

 

[Jarvis323]

For reference, here are some examples of misleading articles about reversals.

https://www.usgs.gov/faqs/it-true-Earth's-magnetic-field-occasionally-reverses-its-polarity?qt-news_science_products=0#qt-news_science_products

https://www.nasa.gov/topics/earth/features/2012-poleReversal.html

https://www.ngdc.noaa.gov/geomag/faqgeom.shtml#How_often_does_the_magnetic_field_reverse

I would be surprised if anyone could find an article who's audience is the public, predating the recent news, that isn't misleading.

 

[Baluncore]

Why do you reference and focus on articles you believe are misleading? Surely that is not going to enlighten your readers. Nor will it help test your unspecified, or non-existent hypothesis.

What mechanisms have you identified or considered, that might connect Earth's magnetic field to climate?

 

[Jarvis323]

Why do you reference and focus on articles you believe are misleading? Surely that is not going to enlighten your readers.

Why not? If the information that the majority of people have been getting about something is wrong or misleading, why would it not enlighten readers to be informed of that and to have the confusion corrected?

 

[Jarvis323]

...Nor will it help test your unspecified, or non-existent hypothesis.

My hypothesis about climate and reversals is non-existent.

 

[jim mcnamara]

We are not doing Science here. Hopefully you are aware that you cannot prove the Null Hypotheis - something not there or does not exist. The reason is to prove the assertion requires testing ALL possible cases. You cannot see all possible cases.

Thanks to everyome for participating. Thread closed.