Antarctica’s unique gravitational field, long recognized as the planet’s strongest “gravity hole,” is now understood to be the result of sluggish movements in the Earth’s mantle over tens of millions of years, according to a study published in Scientific Reports.
For decades, scientists have known that gravity is measurably weaker over the Antarctic continent than in most other regions of the world. This isn’t a minor fluctuation; the reduced gravitational pull causes the ocean surface to sit lower relative to Earth’s center, as water flows towards areas of stronger gravity. The depression is substantial and measurable using data from GRACE (Gravity Recovery and Climate Experiment) satellites.
The new research reconstructs the history of this gravitational anomaly, tracing its origins back 70 million years – to a period before Antarctica was covered in ice. The study reveals a connection between the slow movement of rock deep beneath the Earth’s surface and the formation of the gravity hole. Specifically, the research points to the interplay between sinking slabs of ancient seafloor along Antarctica’s margins and broad thermal upwellings within the continent’s interior.
As hot material rises through regions where gravity’s response is particularly sensitive to density changes, it amplifies the gravitational low at the surface. This process, researchers say, represents an “intricate dance” between geological forces.
The gravity hole is centered over Wilkes Land in East Antarctica. Geophysical observations, including gravity anomalies and subglacial topography, have led to a hypothesis that a giant impact structure – the Wilkes Land crater – lies buried beneath the ice sheet. First proposed in 1962 by Richard A. Schmidt based on data from the U.S. Victoria Land Traverse, the crater is estimated to be 243 kilometers (151 miles) across and at least 848 meters (2,782 feet) deep. Yet, the existence of the crater remains unconfirmed due to the lack of direct bedrock samples.
The Wilkes Land anomaly, a large-scale gravity anomaly associated with a subglacial depression, has been linked to the potential impact structure. A specific positive gravity signal, known as the Wilkes Land mascon, detected by satellite gravimetry, is similarly interpreted by some as evidence of a large impact basin. The hypothesized crater is approximately 315 miles across.
The research utilizing GRACE satellite data calculates geoid variations, which represent departures from a perfect ellipsoid. These variations are based on mass differences within the Earth and the maps pinpoint the location of the deepest geoid depression – the Antarctic gravity hole – for both elliptical and nonhydrostatic measurements. The yellow star on the maps marks the location of this depression.
