How the geographic south and north poles wander

Amazing stuff!

"... as mass shifts deep within our planet, its geographic poles—the tippy top and bottom of Earth, based on its rotation—can also move. Now, researchers have looked back in time to find episodes of the phenomenon, called true polar wander—and they’re more dramatic than we had previously realized.

As plate tectonics and the natural churning of the mantle shuffle around matter inside Earth, the planet’s spin changes slightly. To get back on balance, Earth’s interior slides around on the dense molten core, causing the geographic poles to shift as well. To look for such periods in the geologic past, researchers analyzed records of flooding and drying over the past 320 million years.

They sought a four-leaf clover pattern characteristic only of true polar wander, where opposing halves of the northern and southern hemispheres drown and dry out—a consequence of the continents shifting in and out of the equatorial region, where Earth’s spin makes water bulge.

The clover pattern arose roughly 20, 90, 140, and 190 million years ago. Today, true polar wander occurs at about 10 centimeters per year—too minimal to notice. But when it accelerates, major changes to Earth’s biosphere and climate can result.

 ..."

"On Earth, everything is moving. The planet spins, the tectonic plates shift and the spin axis wobbles as do the magnetic poles, which makes determining how things move a rather tricky proposition. ...

Since the spin axis of the Earth usually overlaps with the magnetic pole, at least in recent geologic history, researchers can use the magnetic pole as a proxy for the spin axis. ...

Our results indicate that around 56-48 million years ago, the entire solid Earth reoriented relative to the spin axis, which gave us the jump found in the paleomagnetic record.” ..."

From the editor's summary and abstract (1):

"Editor’s summary

True polar wander (TPW), which occurs when the solid outer Earth shifts relative to its spin axis, is difficult to detect with standard approaches using paleomagnetic measurements. Domeier et al. used a different strategy to detect TPW in the Mesozoic Era using reconstructions of sea level as a proxy.

They found a robust quadrupolar pattern that reflects global sea-level fluctuations associated with relative changes in centrifugal potential that occurred due to rapid TPW. This demonstrates that coupling in Earth’s rotational dynamics, mantle processes, and surface environments can be highly episodic. ...

Abstract

True polar wander (TPW) is presently occurring at a rate of ~10 centimeters per year, exceeding the mean rate of differential plate motion. Whether this rate is transient and negligible on geological timescales or whether Earth has experienced rapid TPW lasting millions of years is unclear.

Paleomagnetic evidence has been used to propose fast episodes of TPW, but limitations of the paleomagnetic record have precluded definitive results. Rapid TPW will induce global sea level fluctuations associated with relative changes in centrifugal potential, offering an independent test. We evaluated this prediction using continental flooding reconstructions and identified multiple robust quadrupolar patterns since 320 million years ago, confirming that protracted rapid TPW has occurred on Earth and that couplings among Earth’s rotational dynamics, mantle processes, and surface environments can be strongly episodic."

From the abstract (2):

"It is well established that the Hawaiian hotspot moved southward relative to the spin axis in Paleogene time.

Two contrasting prior explanations are:
(a) reorientation of the solid Earth relative to the spin axis (i.e., true polar wander (TPW)), and
(b) independent southward motion of the Hawaiian hotspot through the mantle. Here we distinguish between these hypotheses by determining a new chron C24r (56 Ma) Pacific plate paleomagnetic pole from skewness of marine magnetic anomalies. This extends a set of Pacific plate spin-axis locations for which the repeatability is 2–5.5 times better than for coeval continental paleomagnetic poles. The new pole extends the northward progression of the prior 73–58 Ma Pacific plate apparent polar wander (APW) track such that it overlaps the southern end of the 48–12 Ma track.

From 56 to 48 Ma (between two intervals of true polar stillstand) either the Pacific plate moved rapidly southward relative to the mantle (with even faster southward motion of Pacific hotspots with both Hawaii and Louisville hotspots moving south) or TPW occurred.

The reconstructed plate geometry and relative plate motions are inconsistent with ancient plate driving forces having caused the observed southward motion relative to the spin axis.

The best explanation is an ∼6°–7° episode of TPW, but motion between hotspots and some southward motion of all Pacific hotspots through the mantle may also have occurred. The hypothesized TPW episode occurred near the end of the Early Eocene Climate Optimum and the onset of Cenozoic cooling."

ScienceAdviser

Quadrupolar sea level fluctuations reveal episodes of rapid polar wander (1, no public access)

Rice researchers find evidence of true polar wander (original news release) "Anomalous movement in Pacific plate record may be explained by movement of entire solid Earth relative to its spin axis"

Changes in Latitude of Pacific Hotspots From ∼56 Ma to ∼48 Ma Inferred From Pacific Plate Apparent Polar Wander Before and After Chron C24r: Implications for True Polar Wander (2, no public access)

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