A new study shows that slow, deep rock currents inside the Earth have helped shape the planet's strongest large-scale gravitational anomaly under the Antarctic continent.
Why is gravity weaker over Antarctica than anywhere else on the planet? And how did this spectacular anomaly become established and then durably reinforced over Earth's history?
A new study published open access in
Scientific Reports provides decisive answers. Conducted by a team from the Institut de Physique du Globe de Paris (IPGP), this research received major support from the Make Our Planet Great Again (MOPGA) initiative, funded by the Agence nationale de la recherche (ANR).
Going back in time to the planet's core
To understand the origin of this unique gravity low, the researchers reconstructed the evolution of Earth's internal dynamics over nearly 70 million years. This "gravity low" does not correspond to a physical hole, but to a vast undulation in the Earth's gravitational field, linked to a mass deficit. Their approach combines images from seismic tomography — comparable to X-rays of the globe's interior obtained from seismic waves — with physical models describing the extremely slow deformation of mantle rocks.
This method produces a veritable "animated history" of deep currents under Antarctica, and allows their evolution to be tracked over geological timescales.
A deep engine changing its mode of operation
The results reveal a major turning point between approximately 50 and 30 million years ago. Initially, the gravity low was primarily linked to the sinking of cold, dense rocks towards mantle depths along the Pacific and South Atlantic margins of the Antarctic continent.
Then, progressively, a different dynamic took hold: a vast column of hot, lighter rocks, located under the Ross Sea and several thousand kilometers wide, rose from great depths towards the upper mantle. This slow but continuous upwelling profoundly altered the mass distribution under the continent.
The formation of an extraordinary gravitational anomaly
The combination of these two processes — the sustained sinking of cold rocks on the continent's margins and the upwelling of hot material beneath its center — strongly accentuates the mass deficit under Antarctica. The gravity low then stabilized in its current position and reached the exceptional intensity observed today, making this region the planet's largest continental gravitational anomaly.
When mantle dynamics influence the surface
This key period in Earth's internal evolution coincides with a slight but well-documented shift in the planet's rotational axis, known as
true polar wander, around 50 million years ago. The study thus establishes a direct link between deep mantle circulation, the large-wavelength variations of the gravitational field measured at the surface, and subtle, yet global, changes in Earth's behavior.
What this study changes in our understanding of Earth
By tracing the evolution of the Antarctic gravity low over several tens of millions of years, this work provides an integrated view of the links between internal dynamics, the gravitational field, and the planet's rotation. It shows how processes that are slow and invisible on a human scale can leave a measurable signature on the globe's surface, and even influence Earth's orientation in space.
Schematic cross-section under Antarctica illustrating the geoid low (gravity anomaly). The sinking of cold, dense rocks (subducting plates) on either side, combined with an upwelling of hot rock at the center, creates a mass deficit, which translates into slightly weaker gravity above the continent (black arrows). Vertical deformation is exaggerated. This conceptual diagram synthesizes the mantle density structure and flow pattern under Antarctica predicted by convection reconstructions.