Topography and gravity anomalies are two fundamental observations on the Earth's surface. The topographic relief on Earth reaches up to several kilometers. What mechanisms support the Earth's surface topography and where are the gravity anomalies come from? The two most significant contributions are the flexure and isostasy of the Earth's lithosphere, as well as the mantle convection within the Earth's interior.
Recently, Dr. YANG An of Prof. SUN Weidong's team from the Institute of Oceanology of the Chinese Academy of Sciences (IOCAS), Prof. Watts. A.B. from Oxford University and Prof. ZHONG Shijie from University of Colorado at Boulder collaborated to reveal the nature of the transition from flexural isostasy to mantle dynamics.
The study was published in Earth and Planetary Science Letters on Feb. 17.
The researchers analyze gravity anomaly and topography (bathymetry) data in Pacific Ocean and use the observed admittance at wavelengths from ~200 km to ~5000 km together with combined plate flexure and mantle flow models to determine the nature of transition from flexural isostasy to mantle dynamics. "We found a transition wavelength of ~600 km such that flexural isostasy dominates at wavelengths shorter than ~600 km, while mantle dynamics dominates the topography and gravity for wavelengths longer than ~600 km," said Dr. YANG An, first author of the study.
Mantle flow models based on different seismic tomography models have been used to determine the main controls on the dynamic admittance at wavelengths between 600 and 5000 km for the Pacific. Researchers found that the observed admittance is best explained by a temperature-dependent viscosity mantle and a weak asthenosphere with viscosity that is a factor of ~20 smaller than the mantle transition zone and ~600 smaller than the lower mantle.
"Our results provide new insight in understanding where the influence of mantle dynamics ends and the lithosphere begins," said Dr. YANG.
Bathymetric and gravity of the North Pacific Ocean centered on Oahu Island in a window of 5000×5000 km. (Image by IOCAS)
Yang An., Watts. A.B., & Zhong Shijie. (2025). The relationship between gravity anomalies and topography in the Pacific Ocean and its implications for flexural isostasy, mantle viscosity and dynamics. Earth and Planetary Science Letters, 655, 119246.
(Text by YANG An)
Media Contact:
ZHANG Yiyi
Institute of Oceanology
E-mail: zhangyiyi@qdio.ac.cn
(Editor: ZHANG Yiyi)