MercoPress. South Atlantic News Agency

Under Antarctic ice, Earth’s deepest gravity “low” points to a 70-million-year story

The authors report that at the beginning of the Cenozoic, the location of the maximum global geoid depression was centered over the South Atlantic

A new study has reconstructed the evolution of the planet’s strongest nonhydrostatic geoid depression —the Antarctic Geoid Low (AGL)— finding that the feature has persisted for at least 70 million years and underwent a major shift in both position and strength between roughly 50 and 30 million years ago.

Today, the anomaly appears as a gravity “low” centered over the Ross Sea, between Victoria Land and Marie Byrd Land. It is imperceptible at human scale, but it reflects real spatial variations in Earth’s gravity field and can translate into subtle differences in sea-surface height because gravity helps shape how ocean water is distributed.

Published in Scientific Reports, the research aimed to move beyond present-day gravity snapshots by reconstructing “the long-term evolution of the geoid over the past 70 million years,” using mantle-convection modeling constrained by seismic-tomography-based density structure.

The authors report that at the beginning of the Cenozoic, the location of the maximum global geoid depression was centered over the South Atlantic (roughly 30°S–45°S). The minimum then shifted rapidly toward the Ross Embayment between 40 and 30 million years ago. They identify the 50–30 million-year interval as a “robust transition” window in the AGL’s evolution across model tests.

The study describes two phases in amplitude: from 70 to 35 million years ago, the anomaly fluctuated; from 35 million years ago to the present, it strengthened by about 30%. The paper links this long-term intensification to changing buoyancy contributions within the mantle at different depth layers and to the role of an anomalously hot, buoyant mantle upwelling beneath the Ross Embayment.

The timing of the strengthening overlaps with a pivotal climate shift: the Eocene–Oligocene transition, when Earth moved toward “icehouse” conditions and Antarctica experienced its first major glaciation around ~34 million years ago. The paper does not claim a direct cause-and-effect relationship, but it flags the coincidence as a basis for further work on how deep-Earth dynamics might connect to surface observables such as sea level and long-term ice-sheet development.

Modern detection and mapping of such gravity-field variations rely on satellite gravimetry. NASA notes that missions like GRACE map Earth’s gravity field by tracking the distance changes between two co-orbiting satellites, enabling precise measurements tied to mass distribution across the Earth system.