True Polar Wander (TPW)

What is TPW (and what is it not)?

True polar wander (TPW) is the reorientation of a planet’s rotation pole from the perspective of the planet itself. This process is different from precession, in which the rotation pole changes its orientations in space, pointing towards different “North Stars” over time.

Using the Earth as an example, TPW occurs if the North Pole of the Earth drifts away from its original location towards, let’s say, North America.

It is important to also not confuse the rotation pole with the magnetic pole; TPW concerns the rotation pole.

In true polar wander (TPW), the rotation axis (red dot above) remains fixed in (inertial) space. TPW would not cause the pole to point towards another North Star. Instead, the planet itself reorients with respect to its rotation axis, so a person standing at an high-latitude location might observe that the North Pole is 'drifting' farther and farther away.

Why study TPW?

TPW is a consequence of mass redistribution on or inside the planet. Examples include the formation of large ice sheets, or “plumes” arising from convection in the planetary mantle. TPW also influences the location of the planet’s rotational bulge, and shifts the latitude of continents and oceans. Therefore, it is an important signal in many planetary changes such as climate, sea level, and mantle convection, both in the geological records and in future projections.

My contribution to the topic:

In my doctoral work, I developed a pair of new theories of TPW (corresponding to different time scales) to include the effects of elastic strength in the Earth’s lithosphere.

The lithosphere, which includes the crust, can maintain a planet’s initial rotational bulge shape over a very long time as TPW forces the bulge to adjust to the new rotation pole. This resistance can slow or even stop TPW.

Together with my doctoral advisor and colleagues, we have shown that the Earth’s pole had not moved as much or as easily as previously thought, suggesting that new interpretations of some geological records may be necessary. On the other hand, features of the new theories also enabled us to explain the physical mechanisms behind some other major TPW events seen in the geological data. We have also refuted a theory that suggested the Earth’s last ice age ended due to TPW.

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