Antarctica has a ‘gravity hole’

A “gravity hole” beneath Antarctica sounds like the plot to a bad sci-fi movie, but it’s a very real situation deep beneath the Earth’s surface stretching back tens of millions of years. The phenomenon thankfully isn’t as apocalyptic as it sounds, either. In fact, researchers say these complex interactions between rock densities, gravitational pull, and sea levels are actually helping them understand how the southernmost continent’s ice sheets evolved, and what their influences mean for the planet’s climate.

Most people experience gravity as a constant in their lives. In reality, the force exerts itself differently depending on the location and relationships between objects of varying mass. Inside the Earth’s mantle, rock density disparities gradually affect ocean environments. Areas of weaker gravity result in lower ocean surfaces compared to the planet’s center due to the fact that water inevitably flows towards areas of stronger gravity. 

This decreased surface level is the most pronounced in the Antarctic Geoid Low (AGL), otherwise known as the continent’s gravity hole. The AGL wasn’t an overnight occurrence, but one that evolved over millions of years—and multiple phases.The key to analyzing Antarctica’s gravity hole? The continent’s earthquakes, according to a recent study published in the journal Scientific Reports.

“Imagine doing a CT scan of the whole Earth, but we don’t have X-rays like we do in a medical office. We have earthquakes,” Alessandro Forte, a study co-author and geophysicist at the University of Florida, explained in a statement. “Earthquake waves provide the ‘light’ that illuminates the interior of the planet.”

Since humans can barely pick up gravity’s cumulative fluctuations, scientists like Forte must use special equipment to study these changes. They incorporated their earthquake scans into a new physics-based, three-dimensional illustration of Earth’s interior, then compared their map to existing satellite analyses of seismic data. From there, they utilized advanced computer modeling to rewind the geophysics back around 70 million years to simulate how these factors evolved over time.

“By integrating seismic, geodynamic, and mineral-physics data, our reconstructions provide a dynamically consistent view of mantle flow beneath Antarctica and offer new insights into the coupling between deep and shallow mantle processes that govern Earth’s long-wavelength geoid evolution,” the study’s authors wrote.

Forte and colleagues now believe Antarctica’s gravity hole was weaker before eventually intensifying around 30 to 50 million years ago. This corresponds to large-scale changes in the continent’s climate that included the arrival of glaciers. These, in turn, exert major influences on Earth’s ecosystems, including sea levels and ocean acidity.

The team believes their findings strongly suggest regions like the Antarctic gravity hole deserve far more analysis than they currently receive. Forte and colleagues next plan to begin testing for clearer direct links between a strengthening gravity hole and ice sheet development.

“How does our climate connect to what’s going on inside our planet?” asked Forte. “If we can better understand how Earth’s interior shapes gravity and sea levels, we gain insight into factors that may matter for the growth and stability of large ice sheets.”

 

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