Scientists identify three causes of the drift of the axis of rotation of the Earth

A typical desktop globe is designed to be a geometric sphere and to rotate smoothly as you rotate it. Our present planet is much less perfect, both in shape and in rotation.

The Earth is not a perfect sphere. When it turns on its axis of rotation – an imaginary line that crosses the North and South poles – it drifts and wobbles. These rotational axis movements are scientifically called "polar movement". Measurements for the 20th century show that the axis of rotation drifts about 4 inches (10 centimeters) a year. During a century, it is more than 10 meters.

With the help of observational data and models covering the entire twentieth century, NASA scientists identified for the first time three widely ranked processes responsible for this drift: mass loss in Greenland, the glacial rebound and convection of the mantle.

"The traditional explanation is that a process, the glacial rebound, is responsible for this movement of the earth's axis of rotation.But recently, many scholars have speculated that others processes could have significant effects on him, "said the first author Surendra Adhikari. Jet Propulsion Laboratory in Pasadena, California. "We have assembled models for a suite of processes considered important for the movement of the axis of rotation.We have identified not one but three sets of crucial processes – and the melting of the global cryosphere (especially in Greenland ) of the 20th century is one. "

In general, the redistribution of the mass on and within the Earth – such as changes in the land, ice caps, oceans and mantle flow – affects the rotation of the planet. As temperatures rose throughout the 20th century, the ice mass in Greenland decreased. In fact, about 7,500 gigatons in total, the weight of more than 20 million Empire State Buildings, from Greenland ice melted into the ocean during this period. This makes Greenland one of the major contributors of mass transferred to the oceans, causing sea level rise and, as a result, drifting the axis of rotation of the Earth.

While ice melting occurs in other places (such as Antarctica), the location of Greenland makes it a greater contributor to the polar movement.

"There is a geometric effect that if you have a 45-degree mass in relation to the North Pole – what Greenland is – or the South Pole (like the Patagonian glaciers), this will have a greater impact on the rotation of Earth "is close to the pole," said co-author Eric Ivins, also of the JPL.

Previous studies have identified glacial rebound as a key factor in long-term polar movement. And what is the glacial rebound? During the last ice age, heavy glaciers depressed the surface of the Earth, much like a mattress depresses when you sit on it. As the ice melts or is removed, the earth slowly returns to its original position. In the new study, which was largely based on a statistical analysis of this rebound, scientists understood that the rebound of glaciers would be responsible for only about a third of the polar drift in the twentieth century.

The authors argue that mantle convection is the last third. Mantle convection is responsible for the movement of tectonic plates on the surface of the Earth. It is essentially the circulation of matter in the mantle caused by the heat of the Earth's core. Ivins describes it as a pot of soup placed on the stove. As the pot or mantle heats up, the pieces of soup begin to rise and fall, essentially forming a pattern of vertical circulation, just like the rocks moving in the Earth's mantle.

With these three major contributors identified, scientists can distinguish between mass changes and polar movements caused by long-term terrestrial processes over which we have little control over those caused by climate change. They now know that if the loss of ice in Greenland accelerates, the polar movement will probably be too.

Explore more:
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More information:
Polar Movement Simulator: vesl.jpl.nasa.gov/sea-level/polar-motion/