Antarctica sits above the strongest negative gravity anomaly on Earth. The gravitational acceleration at the surface is measurably weaker than it should be for a continent of its size and elevation. The deficit is large enough that the ocean surface in the surrounding Southern Ocean sits lower — seawater flows away from regions of weaker gravity toward regions of stronger gravity, leaving a shallow depression centered on Antarctica. Satellite measurements of Earth's geoid — the hypothetical ocean surface determined by gravity alone — show the Antarctic low clearly. It has been known for decades. What produces it was not.
Researchers at the University of Florida and the Paris Institute of Earth Physics (Scientific Reports, 2026) used seismic tomography — earthquake waves as a CT scanner for Earth's interior — to reconstruct the history of the mantle beneath Antarctica. The gravity hole formed from two processes operating on different timescales.
First, ancient tectonic slabs that subducted beneath Antarctica sank deep into the mantle. Dense subducted material descending into the lower mantle altered the density distribution far beneath the surface. Second, a broad region of hot, buoyant material rose upward through the mantle above the old slabs. The rising plume is less dense than its surroundings, which reduces the gravitational pull at the surface. The gravity deficit is the surface expression of a mass deficit thousands of kilometers below — hot, light rock where cold, heavy rock would produce normal gravity.
The anomaly strengthened between roughly 50 and 30 million years ago. This timing overlaps with the formation of Antarctica's ice sheets. The connection is not direct — ice sheet formation is driven by atmospheric CO2 and ocean circulation — but the deep-mantle processes that shaped the gravity field also influenced the topography that channels ocean currents around the continent. The processes that produced the gravity hole may have contributed to the isolation that made glaciation possible.
The deficit is a window downward. Surface gravity, measurable from satellites, encodes the density distribution thousands of kilometers below. The mantle cannot be observed directly, but its gravitational signature reaches the surface undistorted.
University of Florida and Paris Institute of Earth Physics, "Antarctica's gravity hole," Scientific Reports (2026).