Gravity Hole Beneath Antarctica: Origins and Climate Impact

Beneath Antarctica’s vast ice sheet lies a remarkable gravitational anomaly known as the Antarctic Geoid Low (AGL), or “gravity hole.” This feature, which emerged over 70 million years ago in the dinosaur era, poses no direct threat to humanity but offers crucial insights into Earth’s past.

It aids scientists in unraveling the development of the Antarctic ice sheet and its role in worldwide climate shifts, as detailed in reports from Popular Science and recent studies in Scientific Reports.

What is the Antarctic Geoid Low (AGL)?

The Antarctic Geoid Low (AGL) is a zone above the Ross Sea where Earth’s gravitational pull is the weakest globally. In this area, ocean levels dip about 130 meters (roughly 420 feet) below the global average, as water flows toward regions with stronger gravity.

This gravity hole isn’t a physical crater but a dip in the gravitational field caused by lower-density rock in the mantle beneath the continent.

Earth’s gravity isn’t uniform; it fluctuates based on the mass and density of subsurface rocks. In areas with less dense materials, like under Antarctica, the pull is weaker, affecting ocean water distribution.

This effect is most pronounced in the AGL region, where the geoid—the Earth’s shape approximated by sea level—shows the deepest negative anomaly.

Origins of the Gravitational Anomaly: From Dinosaurs to Today

Research by geophysicists Alessandro Forte from the University of Florida and Petar Glišović from the Institut de Physique du Globe de Paris, published in Scientific Reports, indicates the gravity hole began forming around 70 million years ago.

During the dinosaur age, less dense rocks accumulated in Antarctica’s mantle due to slow convective movements—processes where hot materials rise and cooler ones sink.

Initially mild, the anomaly intensified between 50 and 30 million years ago, coinciding with dramatic Antarctic climate changes as the continent froze over, creating its current ice sheet.

Using global seismic data and computer simulations, researchers “rewound” time to trace AGL’s evolution. These mantle flows, moving at a few centimeters per year, still influence gravity today.

VIDEO. Mysterious Giant Hole in Antarctica Explained | WION Podcast.

Measurements and Discoveries: Satellites and Seismology’s Role

The anomaly was first precisely measured using satellites like GOCE (Gravity Field and Steady-State Ocean Circulation Explorer) from the European Space Agency.

This data revealed AGL spans a vast area under the Ross Sea and is Earth’s deepest gravitational depression. Seismic waves from earthquakes helped map the planet’s interior, confirming the involvement of less dense rocks.

The study also links the gravitational anomaly to plate tectonics: Antarctica was once part of the supercontinent Gondwana, and continental breakup affected the mantle. This explains similar, though milder, anomalies in the Indian Ocean or under the North Pole.

Impact on Climate and Earth’s Future

The gravity hole under Antarctica isn’t just scientifically intriguing; it has real-world implications. It influences the stability of the Antarctic ice sheet, which holds 70% of the planet’s fresh water.

Gravitational changes could accelerate ice melt, contributing to sea level rise. Experts believe understanding AGL will improve climate predictions, as gravity variations affect ocean currents and heat distribution.

While the phenomenon doesn’t directly endanger humans, it highlights Earth’s dynamic nature. Upcoming missions like GRACE-FO will continue monitoring to better grasp the evolution of Earth’s gravity and its part in global warming.