Most of us think of gravity as a stable, constant value, but in reality, its strength varies across the Earth. Variations are influenced by the Earth’s shape, rotation, and mass distribution, including its geological structure.
One area where gravity is significantly weaker is the gravitational hole at the South Pole. This is not a physical cavity in a continent, but an area where the Earth’s gravitational pull is slightly weaker than average. This corresponds to a deep geoid cyclone, a depression in the planet’s theoretical oceanic surface caused by fluctuations in the mass distribution in the underlying mantle.
Even small differences in gravity have a measurable effect on sea level. In areas of weaker gravity, sea levels are slightly lower relative to the center of the Earth as water masses move to areas of stronger gravity. As a result, the sea level around Antarctica decreases.
The study, led by Dr. Petar Grisovic of the Paris Institute of Geophysics and co-authored by Dr. Alessandro Forte, professor of geophysics at the University of Florida, showed that the gravity hole was formed over tens of millions of years by the extremely slow movement of rocks deep inside the Earth.
The researchers also found that historical changes in anomalies appear to coincide with major climate changes in Antarctica. Scientists say future research could reveal how changes in gravity affect the growth of continental ice sheets.
Alessandro Forte said: “A better understanding of how Earth’s interior shapes gravity and sea levels will provide insight into the factors important to the growth and stability of large ice sheets.”
Researchers have reconstructed subtle changes in Earth’s gravitational shape, both present and past. Current maps from GRACE satellite data show distinctive global geoid patterns, including deep gravity lowlands near the South Pole. These maps distinguish between anomalies related to Earth’s geometry and those caused by deeper mass fluctuations within the planet.
To understand how this feature evolved, scientists generated time-dependent geoid projections for key moments in Earth’s history: about 65 million years ago, 40 million years ago, and now.
The study combined global seismic records with physical models to reconstruct the three-dimensional interior of the Earth.
“Imagine performing a CT scan of the entire planet. We don’t have X-rays like in a medical setting. Instead, we use earthquakes. Seismic waves provide the ‘light’ that illuminates the planet’s interior,” Forte explained.
Scientists were able to reconstruct a global gravity map that matched satellite gravity data, corroborating their model. Their computer simulations also reproduced the patterns of rock flow within the deep interior and traced its evolution back 70 million years.
The results suggest that the gravitational hole was initially weak, but began to strengthen between 30 and 50 million years ago. This period coincides with significant climate change in Antarctica.
As part of further research, scientists aim to uncover connections between Earth’s climate and the Earth’s internal workings. They plan to use the new model to investigate the relationship between gravity, sea level, and changes in continental elevation.
References:
1 Cenozoic evolution of Earth’s strongest geoid cyclone reveals the dynamics of the Antarctic subsurface mantle – Petar Glišović et al. – scientific report – December 19, 2025 – DOI: 10.1038/s41598-025-28606-1