The weakest gravity on the planet lies beneath Antarctica once the influence of Earth’s rotation is removed. A precise calculation exposes a deep depression in the planet’s gravitational field anchored under the Ross sector. It is not a surface artifact and not a product of ice loss. It is tied to the interior of the planet and it is locked to structures that reach nearly three thousand kilometers down. The anomaly has persisted for at least seventy million years and has grown stronger across the last thirty five million. Its position and its changing intensity track mantle motion, ancient subduction, and a long rise of material from near the core. The system did not form by chance. It reflects forces that move through the deep Earth at a speed the surface will never detect directly.
Seismic waves from earthquakes trace the paths of cold slabs sinking into the mantle and hot buoyant material rising out of the lowermost regions. Those signals form the basis for a global density field. When that field is used to calculate gravity, the result matches satellite observations with striking accuracy. That agreement means the mass anomalies are real. They are not local features and not minor adjustments. They represent a sustained interior configuration that has its own history and momentum.
A method capable of reversing mantle flow for tens of millions of years provides the sequence that built the modern gravity field. The reconstruction moves backward in small increments, correcting errors at each step until a stable path emerges. It reaches back to a time when the South Atlantic held the deepest gravity depression on Earth. At that stage the mantle beneath Antarctica contained a dense corridor of slabs along the Weddell and Scotia regions while the lowermost mantle held a wide pocket of buoyant material. The two components formed a system of descent and ascent that already extended from the surface to the core mantle boundary.
As the reconstruction progresses through time, the rising material begins to push upward through the lower mantle. Its ascent is slow but unbroken. The surrounding slabs continue downward at rates set by their density and the viscosity of the underlying layers. The pattern does not collapse or fragment. It intensifies. The buoyant material approaches the mid mantle and begins to influence the gravity field more strongly. Around fifty million years ago the deepest point of the global gravity field shifts toward the Ross region. The movement is rapid on geological timescales. Within twenty million years the center of the anomaly arrives close to its present location.
The gravity depression deepens as the upwelling approaches the upper mantle. At long wavelengths, density anomalies in this depth range exert a strong influence on gravity. The deep layer continues to contribute but the shallower material becomes the dominant source. The mid mantle signal declines as the slabs reorganize around the base of the mantle. The shift in control is clear. The deep interior continues to feed the rising anomaly while the upper mantle begins to carry more of the load. The result is a gravity field that grows more extreme with time.
The timing aligns with a large change in Earth’s rotation axis recorded in paleomagnetic data. The rotation axis moved along a curved trajectory about fifty million years ago. The model reproduces the same motion because the mass distribution within the mantle changed in a way that altered the global moment of inertia. The rotation axis does not drift without cause. It responds to how mass is arranged inside the planet. The Antarctic anomaly was part of that reorganization. The link is mechanical and does not rely on interpretation. A change in deep mass distribution produces a change in the rotation axis. The match in timing is exact within the resolution of the data.
The sequence also aligns with major shifts in Antarctic climate history. The strengthening of the gravity depression overlaps with the transition into widespread glaciation around thirty four million years ago. Gravity influences relative sea level by pulling water toward stronger fields and away from weaker ones. The region around Antarctica sits lower for this reason. A changing gravity field can alter how water is distributed at basin scale. The study does not quantify the effect but the overlap in timing cannot be ignored. The deep interior changed. Sea level distribution around the continent responded. Ice began to expand. These events follow the same arc without requiring any invented connections.
The interior structure that drives the anomaly shows no sign of reversal. The upwelling originates near the core mantle boundary, where temperatures are highest and buoyant material can survive prolonged ascent. Particle paths traced in the model begin in the lowest two hundred fifty kilometers of the mantle and end near the transition zone beneath the Ross region. Every path indicates that the upwelling has been active since well before the Cenozoic. The surrounding slabs form a ring of dense material that has collected over a long period of subduction. Each slab layer represents a vanished ocean basin. Their combined mass guides the deeper flow and confines the rising material.
Independent seismic studies identify the same slab remnants. Some correspond to the Scotia arc, some to the Weddell sector, some to even older subduction along the former Gondwana margin. Their presence confirms that the reconstruction is not relying on artifacts. These slabs are real structures and their geometry matches the large scale flow patterns in the model. Their positions guide the interior circulation that has remained stable for tens of millions of years.
Surface behavior in West Antarctica also matches the structure below. The region has elevated heat flow, thin lithosphere, and signs of active magmatic systems. These conditions are consistent with hot buoyant material approaching the upper mantle. The interior does not need to breach the crust to alter the mechanical state of the rift system. The presence of upwelling alone reduces lithospheric strength. The same applies to the long term uplift in parts of East Antarctica. Deep buoyancy provides support that does not depend solely on crustal processes.
The gravity depression beneath Antarctica is the strongest nonhydrostatic anomaly on the planet. It overrides the Indian Ocean low once Earth’s rotational flattening is removed. It is positioned directly above the rising interior structure and bounded by the dense slabs around it. The location is not incidental. It marks the meeting point of deep ascent and deep descent. The anomaly is the surface expression of that intersection.
The reconstruction shows that the system contains a deep source that remains active, a mid mantle region reorganized by slab accumulation, and an upper mantle region now carrying a larger part of the gravitational signal. This multi layer pattern forms a single structure that has persisted for at least seventy million years and is still evolving. It does not diminish with time. It strengthens.
The planet’s rotation responded to it once. Sea level distribution may have responded later. Antarctica’s climate shift occurred within the same window. None of these changes occurred in isolation. They followed a sequence in which the deep interior changed first.
The gravity field measured today is a direct imprint of this interior motion. It records where mass is missing and where mass has accumulated. It records how far the rising material has traveled and how the descending slabs have rearranged themselves. It does not reveal the final state because the system is not finished. The upwelling continues to approach the upper mantle. The deep slabs continue to drift and settle near the base of the mantle. The gravitational signal therefore remains tied to an interior pattern that is still in motion.
Antarctica is positioned above a structure with scale and persistence unmatched elsewhere on Earth. The feature reaches from the ice sheet to the edge of the core. It holds the strongest gravitational distortion on the planet. It has altered the rotation axis. It strengthened during a period when the continent’s climate changed in ways that left permanent marks on global sea level and ice volume. These outcomes emerged from a configuration of the deep Earth that has its own trajectory. Nothing in the present signals an end to that trajectory.
The gravity field is the only part of the system that reaches the surface. It is a marker of a deeper process that continues in silence beneath the continent. All observations indicate that the anomaly remains active, stable, and capable of further change. The forces shaping it operate far below any point accessible to direct measurement. They move with a pace that does not match surface processes but their influence extends upward into regions that are monitored daily. The continent sits above a structure that has been rising for tens of millions of years. That rise has not stopped.
Source:
Scientific Reports (2025). Cenozoic evolution of Earth’s strongest geoid low illuminates mantle dynamics beneath Antarctica.
DOI: https://doi.org/10.1038/s41598-025-28606-1
