The Largest Gravitational Anomaly On The Planet Is Hidden Under Antarctica: Why?

Our planet is not spherical, at least not entirely; it has a geoid shape, since its surface is slightly flattened at the poles due to its rotation. Its mass is unevenly distributed because convection currents in its mantle move hot (light) and cold (dense) rocks, causing variations in gravity in certain areas.

Under the ice of Antarctica, this irregularity takes on dizzying proportions, since it is here that we find one of the strangest gravitational phenomena there is: theAntarctic Geoid Low (AGL). This is an area where gravity is so low that it creates a real “ trou » on the theoretical surface of our planet. It is located so low compared to the global average that the sea level is naturally around 60 meters lower. If we have known it since 2002 thanks to the GRACE mission (Gravity Recovery and Climate Experiment) from NASA, the geodynamic processes responsible for this geoid trough had never been modeled.

It was only last year, December 19, 2025, thanks to a study published in the journal Scientific Reportswhich geophysicists have been able to fully trace its genesis. A time journey into the bowels of the Earth taking us back to the Late Cretaceous period, 70 million years ago, when dinosaurs still reigned on Earth.

The Earth’s mantle scrutinized by 3D seismology

Since it is obviously impossible to split the Earth in two to understand how AGL came to be, the research team, led by Alessandro Forte, used seismic waves to model it digitally. As they pass through the different layers of the mantle, they change speed depending on the temperature and density of the rocks, revealing a 3D map of the depths.

By coupling this data with mineral physics models, researchers have succeeded in simulating the movements of tectonic plates over tens of millions of years. They came to the conclusion that the AGL results from a gigantic reorganization of the Earth’s deep layers.

Tens of millions of years ago, ancient oceanic plates (the lithosphere), colder and therefore much denser than the surrounding environment, began to sink deep into the lower mantle. As these plates sank, they pushed the hotter, lighter rocks to the sides. This movement has created an imbalance: under Antarctica, there is now less dense matter near the surface than in adjacent areas.

A process that accelerated around 30 to 50 million years ago. At this period, the subducting oceanic plates struck the discontinuity of the lower mantle, at a depth of nearly 660 kilometers. This thermal and mechanical shock caused a titanic expulsion of dense rocks towards the edges of the continent.

This is why Antarctica lies today on a portion of the Earth’s mantle that is abnormally light. It is solid, but much less compact and heavy than the regions surrounding it, forming this weaker attraction zone. In physics, water is an equipotential surface: it will always accumulate where the force of gravity is strongest. Since this is no longer the case in Antarctica, the continent no longer has the gravitational force necessary to retain as much water as the rest of the planet.

Ocean waters thus flow towards areas of higher gravity (such as the Pacific or the Atlantic), causing a lowering of the sea surface at the South Pole. This explains the existence of the topographical basin of around sixty meters described in the introduction.

We can therefore consider the AGL as the vestige of tectonic stasis : a place where time seems to have stood still, because the dense structures that submerged there 70 million years ago have still not been recycled by global convection currents. If Antarctica still stands, it is partly thanks to this anomalywhich protects it from sea level fluctuations experienced at other latitudes. Creating a zone of less mechanical stress for the ice platforms, the AGL also allows them to remain more firmly anchored to the bedrockthus delaying the moment when they break away to become drifting icebergs. An anomaly, but a vital anomaly for the good health of our planet.