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Abstract Constraining the long-term evolution of geoid anomalies is essential for unraveling Earth's internal dynamics. While most studies focus on present-day geoid snapshots, we reconstruct the time-dependent evolution of Earth’s strongest geoid depression, the Antarctic Geoid Low (AGL), over the Cenozoic. Unlike geodetic reference frames that place the deepest geoid low in the Indian Ocean, a geodynamic perspective (relative to a hydrostatic ellipsoid) reveals the strongest nonhydrostatic geoid depression actually resides over Antarctica. Using a back-and-forth nudging technique for time-reversed mantle convection modeling, we leverage 3-D mantle density structures derived from seismic tomography and geodynamic constraints. Our results show that the AGL has persisted for at least ~70 Myr, undergoing a major transition in amplitude and position between 50 and 30 Ma. This coincides with abrupt lateral shifts in Earth’s rotation axis at ~50 Ma, validated through paleomagnetic constraints on True Polar Wander. Initially, stable lower mantle contributions dominated the AGL, but over the past ~40 Myr, increasing upper-mantle buoyancy, particularly above ~1300 km depth, amplified the AGL magnitude. This shift stems from the interplay between long-term deep subduction beneath the Antarctic Peninsula and a buoyant, thermally driven upwelling of hot, low-density material from the lowermost mantle. These new results contrast with earlier interpretations, clarifying the crucial role of evolving mantle buoyancy in shaping global geoid anomalies. By incorporating seismic, geodynamic, and mineral-physics data, our reconstructions provide a more comprehensive understanding of mantle flow beneath Antarctica and offer new insights into the dynamic coupling between lower and upper mantle processes that govern Earth’s long-wavelength geoid evolution.
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Validating 70 Million Years of Convection Driven True Polar Wander and Dynamic Flattening with Paleomagnetic Data
Abstract Mantle convection drives changes in Earth's ellipsoidal figure and corresponding moment of inertia, causing shifts in the planet's rotation axis known as true polar wander (TPW). Using seismic tomography and the Back-and-Forth Nudging (BFN) method, we developed a time-dependent convection model that reconstructs the evolution of mantle density distribution and Earth’s moment of inertia over the past 70 million years. This modelling approach provides a close match with independent paleomagnetic constraints on the Cenozoic shifts of Earth’s rotation pole, specifically resolving the previously unexplained U-turn in TPW trajectory at approximately 50 million years ago. Our findings reveal TPW shifts exceeding 5 degrees, despite the temporal stability imposed by high lower-mantle viscosity and the stabilizing effect of Earth's remnant rotational bulge. Verification of our predicted changes in Earth’s ellipsoidal figure through independent paleomagnetic data provides a robust calibration for new predictions of convection-induced dynamic flattening variations. Over the past 70 million years, we find convection-induced changes of flattening that shift from -0.2% to +0.1 % during the Paleogene. Our predictions of Earth's axial precession frequency in the Paleogene align with recent independent cyclostratigraphic studies, thus validating our model's accuracy and supporting the hypothesis of reduced luni-solar tidal dissipation during this period.
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- Award ID(s):
- 1903108
- PAR ID:
- 10636940
- Publisher / Repository:
- Research Square
- Date Published:
- Format(s):
- Medium: X
- Institution:
- Research Square
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Posted Content:
- https://doi.org/10.21203/rs.3.rs-5397333/v1
