Earth's Spin Axis Drift

Venusian Broon

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#3
Me no expert, however I'd guess from reading it that it's not the second explanation you give. It's subtitled the 'observed direction of polar motion'. Doesn't mention magnitude!

From a rough back of a beer mat calculation 5000km south of the current North pole should put you on a latitude of 45 Degrees North and that looks actually north of where the pink line is and south of the pale blue line.

At least two of the components of the this motion/wobble are clearly temporary and will at some point stop, or at least reach a 'maximum effect', so when Greenland loses all of it's ice, or if all the all the postglacial rebound stops then I suspect the motion of the pole will change. Also they state that they know very little about the contribution from the mantle, so possibly over millions of years that changes at random. (?)

Over time (say another ice age) could reverse all these and send the pole the other way, I'd imagine.

EDIT: remember that Earth experiences oscillations in it's axial tilt anyway, varying from 22.1 to 24.5 degrees, caused by gravitational interactions between Earth, the Sun, the moon and the other planets. These movements described in the paper are, I suppose, very tiny perturbations to this main driving force caused by deformations to the Earth's shape.
 
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Robert Zwilling

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#4
From a rough back of a beer mat calculation 5000km south of the current North pole should put you on a latitude of 45 Degrees North and that looks actually north of where the pink line is and south of the pale blue line.
This is where I get confused. What is at a latitude of 45 degrees? That's way down from the current North Pole. The Earth's rotation axis is apparently moving south at a rate of 10 meters a century. The distance on the map is around 5,000 km. I make that to take 500,000 centuries in time, which is 50 million years.

There have been 7 ice ages in the past 50 million years which means there could be multiple times when the ice could be receding or expanding, not just receding as the article seems to be saying. Unless the ice vector they drew takes that into account. The continents have moved around considerably during the past 50 million years, if the time period is 50 million years then the location they show at 45 degrees wont have North America in it the way the article shows it, if North America would even still be there.

The polar regions have been ice free in the past, maybe a couple of times in the last 100 million years. But when I read that, I wonder if Antarctica was ice free because it wasn't anywhere near the south pole but higher up in a warmer region.

If the physical axis is that far down where are the magnetic poles, do they also drift down or stay up on top so to speak. If they start to go towards the equator would they inclined to flip polarity. Do they flip every couple of degrees the axis moves. Are the magnetic poles pointed "upward" controlled by the sun or can they be at any latitude. The magnetic poles have flipped on average every million years for the past 65 million years.
 

Venusian Broon

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#6
This is where I get confused. What is at a latitude of 45 degrees? .
So the circumference of the Earth is ~40,000km. Hence Pole to Equator is ~10,000km, therefore 5,000km, as you stated if you went south of the North Pole must be at latitude 45 degrees.

If the pole axis actually went south at that rate it should therefore be 'there' in 50 million years, but....

There have been 7 ice ages in the past 50 million years which means there could be multiple times when the ice could be receding or expanding, not just receding as the article seems to be saying.
...I believe they are saying that the movement in the past 100 years has been caused by the effects of the three factors that they discuss. And this has caused the axis to slip 10 metres south. So the effects of a warming planet and the last ice age unwinding are the current effects. They are not saying that these factors have existed continually in the past, nor that they will exist continually in the future. In fact I believe they will not - the main driver that makes the Earth oscillate through a range of axial tilts is, as I stated, the Sun and the rest of the Solar system. These movements that the scientists are describing are, I think, a tiny small perturbation that will not have a lasting effect.

So, for example in the immediate future, if Greenland was to fully melt there might be further slippage south, but perhaps in in the near future a new Ice age will 're-ice' Greenland and then the component vector would probably reverse and the pole would tend to go back north.

Unless the ice vector they drew takes that into account. The continents have moved around considerably during the past 50 million years, if the time period is 50 million years then the location they show at 45 degrees wont have North America in it the way the article shows it, if North America would even still be there.
I don't think the map they had was supposed to depict the Earth 50 million years from now. It looks too current!

The polar regions have been ice free in the past, maybe a couple of times in the last 100 million years. But when I read that, I wonder if Antarctica was ice free because it wasn't anywhere near the south pole but higher up in a warmer region.
Polar regions have certainly been ice-free in the past, although if they were just oceans then they will have little effect on the issue of axial wobbliness.

Antarctica and Australia split, I believe, about 50 million years ago, Australia heading north and Antarctica going south, where it is now over the south pole. Having a big plateau of land over the south pole certainly helped form a lot of ice.

If the physical axis is that far down where are the magnetic poles, do they also drift down or stay up on top so to speak. If they start to go towards the equator would they inclined to flip polarity. Do they flip every couple of degrees the axis moves. Are the magnetic poles pointed "upward" controlled by the sun or can they be at any latitude. The magnetic poles have flipped on average every million years for the past 65 million years.
How the magnetic poles work is, I believe, still a problem to solve. Largely I think because we know so little about what exactly is happening deep in the core of the planet. So I'd guess the answer is that we don't know what is the main factor that drives the magnetic field of the Earth.

But yes the magnetic field regularly flips, as we can see that in geological record.

Although there must be some connection with the actual spin of the planet, the magnetic pole wanders about much, much more. See this: Why does the North Pole move?

Unless there is a massive collision with a huge astronomical object I can't see the Earth's axis of rotation deviating beyond what we know, i.e. the 21-24 degree wobble and oscillation of our axial tilt.
 

Robert Zwilling

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#7
Unless there is a massive collision with a huge astronomical object I can't see the Earth's axis of rotation deviating beyond what we know, i.e. the 21-24 degree wobble and oscillation of our axial tilt.
Okay, I got it now. Nothing much is happening with the Earth's axis in the next 50,000 years or so. I'm guessing the displacement of the ice will have a bigger effect on the planet in other ways in the short run. I'm figuring the poles have already melted, just haven't finished melting yet. That means there are three weight displacements. The ice mass disappears on Greenland, the ground underneath rebounds, and the melted ice water goes down around the equator.
 

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