Gainesville, Florida — Beneath the icy expanse of Antarctica lies a gravitational anomaly resembling a potato rather than the expected spherical shape of Earth. This peculiar depression, known as the Antarctic Geoid Low, has been the focus of recent studies that reveal its increasing intensity, tied to geological processes occurring deep beneath the planet’s surface.
Scientists, led by geophysicist Alessandro Forte from the University of Florida, have developed intricate models to understand how this gravitational low has evolved over time. "Understanding how Earth’s internal structure influences gravity and sea levels can provide crucial insights into the stability and growth of significant ice sheets," Forte explains.
Earth’s gravity field varies due to irregular mass distribution within the planet, caused by differences in rock densities. While these variations in gravity are not easily perceptible at the surface, they offer valuable clues about the complex dynamics occurring underground.
Forte and his collaborator, Petar Glišović from the Paris Institute of Earth Physics, utilized seismic data from earthquakes to create a detailed three-dimensional map of the Antarctic Geoid Low. This approach is akin to performing a comprehensive internal scan of the Earth, using the speed and direction of seismic waves to understand subsurface materials. "Earthquake waves act like light illuminating the planet’s inner structure," Forte notes.
The researchers made significant strides in their analysis by comparing their geoid model with established satellite gravity data, which showed a strong correlation. Their next challenge was to trace the development of the geoid over the past 70 million years, beginning from the early Cenozoic era.
By implementing a physics-based simulation of mantle convection, the team effectively rewound Earth’s geological activity to study how the geoid has transformed over time. They also tracked the movement of Earth’s rotational axis, known as True Polar Wander, to see if their model accurately represented these changes.
Findings indicate that the Antarctic Geoid Low has existed for millions of years and has undergone notable shifts in strength and location. Approximately 50 million years ago, these changes intensified, coinciding with a significant alteration in polar wander dynamics. The research posits that descending tectonic plates beneath Antarctica have contributed to this gravitational anomaly, influencing the surface gravity field.
Interestingly, this gravitational shift may link to the onset of major glaciation in Antarctica around 34 million years ago. As the geoid fluctuated, local sea levels likely adjusted accordingly, possibly affecting the development of the continent’s ice sheets. While this connection remains speculative, it underscores the interplay between geological processes, sea level fluctuations, and polar movements.
This groundbreaking research provides insight into the slow yet profound effects of tectonic activities on the planet’s surface. The gravitational anomaly beneath Antarctica serves as a reminder that even subtle geological changes can have enduring impacts on the Earth’s environment and climate. This study is published in the journal Scientific Reports, contributing to the ongoing exploration of Earth’s dynamic systems.