A region beneath Antarctica where gravity is measurably weaker than anywhere else on Earth has puzzled geophysicists for decades. Researchers have now traced the origin of this anomaly, known as the Antarctic Geoid Low, to slow-moving shifts deep inside Earth’s mantle that began roughly 70 million years ago, long before any modern ice sheet existed. The finding connects satellite gravity observations to ancient geological processes and carries direct consequences for how scientists model sea-level change and ice-sheet behavior.
How a 70-million-year mantle shift created the weakest gravity on Earth
The Antarctic Geoid Low is not a gap or a void. It is a broad zone where the pull of gravity registers lower than the global average once the effects of Earth’s rotation are removed. That definition matters because it isolates the signal caused by density variations hidden hundreds of kilometers below the surface. A team at the University of Florida described the feature as Earth’s strongest gravity hole, a label earned by comparing geoid undulations across every continent and ocean basin.
To explain why the anomaly exists, the researchers ran time-reversed mantle convection models, effectively rewinding the slow churn of rock inside Earth by approximately 70 million years. Their results, detailed in a university news release, show that the Antarctic Geoid Low has persisted for at least that entire span. The modeling relied on the GyPSuM tomography dataset, a three-dimensional map of mantle density and seismic wave speeds built from joint seismic and geodynamic inversions. GyPSuM supplied the starting density and temperature fields that the team then projected backward through geological time, revealing that the deep structures responsible for the gravity low were already in place during the late Cretaceous period.
The observational anchor for this work came from NASA’s GRACE and GRACE-FO satellite missions, which measure tiny variations in Earth’s gravitational field by tracking the distance between paired spacecraft. The mascon products generated from those missions provided the benchmark against which the modeled geoid was validated. Without that satellite record, any backward projection of mantle flow would lack a firm present-day reference point, and the inferred history of the anomaly would be far less certain.
In the simulations, dense, cold slabs of ancient oceanic lithosphere sink toward the core-mantle boundary while warmer, buoyant regions rise. Over tens of millions of years, that circulation reorganizes mass in the deep mantle. Because gravity responds to how mass is distributed, not just how much mass there is, the resulting pattern of density contrasts produces subtle highs and lows in the geoid-the hypothetical surface on which Earth’s gravity is perfectly level. The Antarctic Geoid Low emerges in the models as a long-lived expression of these deep density anomalies, tied to the legacy of vanished tectonic plates and mantle upwellings beneath what is now East Antarctica.
Thermal gradients, volcanic heat, and what the geoid low means for ice
One consequence of a gravity anomaly that has lasted tens of millions of years is the thermal environment it implies beneath the ice. A mantle structure stable enough to sustain the Antarctic Geoid Low across the entire Cenozoic era would maintain a persistent thermal gradient in the upper mantle and lower crust. That gradient could locally affect geothermal heat flux beneath the Antarctic ice sheet, a variable that influences basal melting, subglacial lake formation, and ice-stream dynamics.
Testing that connection requires comparing the high-resolution mantle temperature fields produced by models like the one in the Scientific Reports study against direct geothermal flux measurements collected from subglacial lakes and boreholes. If the spatial pattern of elevated heat flux aligns with the deep density anomalies that drive the geoid low, it would confirm that the same mantle architecture shaping gravity also shapes the thermal conditions at the base of the ice. That relationship has not yet been established with field data at the resolution needed, but the modeling framework now exists to guide where those measurements should be taken.
Local geology adds another layer of complexity. Volcanic provinces and rift systems in West Antarctica already point to regions of enhanced heat flow, while the thick, ancient craton in East Antarctica is generally thought to be cooler and more stable. The new mantle models suggest that parts of East Antarctica may nevertheless sit above warmer-than-expected mantle domains associated with the geoid low. If confirmed, that would help explain why some ice streams there move faster than their surface climate alone would predict, hinting at lubricating meltwater produced by a slightly warmer bed.
The practical stakes are tied to sea-level projections. Satellite gravity measurements from GRACE and its successor are used to estimate Antarctic ice mass loss year by year. If the deep mantle signal is not properly separated from the ice-mass signal, estimates of how much ice Antarctica is losing can carry systematic errors. The new study helps define the static, long-lived component of the gravity field so that shorter-term changes caused by melting ice can be isolated more accurately.
Improved separation of these signals feeds directly into global sea-level budgets. When GRACE observes a gravity decrease over Antarctica, that change could reflect ice loss, subsurface water movement, or slow, isostatic rebound of the crust in response to past deglaciation. By constraining the deep, essentially unchanging mantle contribution, researchers can refine how much of the remaining signal must be attributed to contemporary ice dynamics. That, in turn, sharpens projections of coastal risk for communities thousands of kilometers away.
Gaps in the mantle density record and what comes next
Several questions remain open. The GyPSuM tomography model, while the single most critical input to the study, was originally published more than a decade ago. The specific subset of density anomaly data and mineral-physics parameters fed into the 2025 modeling runs has not been released as a standalone dataset. That makes independent replication difficult until the full parameter files are shared.
A related challenge involves separating thermal from non-thermal density components in the mantle. Rock density can change because of temperature, but also because of compositional differences or phase transitions at discontinuities in the mantle transition zone. Earlier work by members of the same research group examined how modeling those discontinuities affects inferred density anomalies, yet the precise inversion weights applied to Antarctic mantle structure in the new study have not been published in detail. Without that information, other groups cannot fully assess how much of the modeled geoid low comes from temperature alone versus chemical heterogeneity.
The raw GRACE mascon time-series files and degree-truncated geoid maps used to validate the model against CSR Release 6.0 geopotential coefficients have also not been made available alongside the paper. NASA’s data archives host the underlying satellite products, but the specific processing choices that connect those products to the study’s conclusions remain internal to the research team for now. Until those processing decisions are documented, subtle biases tied to filtering, leakage correction, or treatment of glacial isostatic adjustment will be hard to quantify.
What to watch next is whether field campaigns in Antarctica begin targeting the locations where the model predicts the strongest thermal gradients beneath the ice. Subglacial drilling projects, seismic deployments, and magnetotelluric surveys could all help map heat flow and crustal structure at finer scales. If those observations converge with the mantle-derived predictions, they would provide a rare, multi-layered view linking processes at the core-mantle boundary to the motion of ice at the surface.
For now, the Antarctic Geoid Low stands as a reminder that Earth’s deepest interior can leave a measurable imprint on modern climate systems. The same slow mantle motions that rearranged continents and closed ancient oceans also set the background conditions for how ice sheets grow, flow, and melt. As satellite missions extend the gravity record and numerical models incorporate more realistic mantle physics, researchers hope to turn that imprint from a curiosity into a quantitative tool-one that improves both our reconstruction of Earth’s past and our forecasts of its sea-level future.
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*This article was researched with the help of AI, with human editors creating the final content.
