Long‐Wavelength Gravity Field Constraint on the Lower Mantle Viscosity in North America

Reusen, J.M.; Root, B.C.; W. Szwillus, W.; Fullea, J.; van der Wal, W.

doi:10.1029/2020JB020484

Long‐Wavelength Gravity Field Constraint on the Lower Mantle Viscosity in North America

Title

Long‐Wavelength Gravity Field Constraint on the Lower Mantle Viscosity in North America

Author

Reusen, J.M. (TU Delft Astrodynamics & Space Missions)
Root, B.C. (TU Delft Astrodynamics & Space Missions)
W. Szwillus, W. (University of Kiel)
Fullea, J. (Dublin Institute for Advanced Studies; Universidad Complutense de Madrid)
van der Wal, W. (TU Delft Physical and Space Geodesy; TU Delft Astrodynamics & Space Missions)

Date

2020

Abstract

The long‐wavelength negative gravity anomaly over Hudson Bay coincides with the area depressed by the Laurentide Ice Sheet during the Last Glacial Maximum, suggesting that it is, at least partly, caused by glacial isostatic adjustment (GIA). Additional contributions to the static gravity field stem from surface dynamic topography, core‐mantle boundary (CMB) topography, and density anomalies in the subsurface. Previous estimates of the contribution of GIA to the gravity anomaly range from 25% to more than 80%. However, these estimates did not include uncertainties in all components that contribute to the gravity field. In this study, we develop a forward model for the gravity anomaly based on density models and dynamic models, investigating uncertainty in all components. We derive lithospheric densities from equilibrium constraints but extend the concept of lithospheric isostasy to a force balance that includes the dynamic models. The largest uncertainty in the predicted gravity anomaly is due to the lower mantle viscosity, uncertainties in the ice history, the crustal model, the lithosphere‐asthenosphere boundary, and the conversion from seismic velocities to density have a smaller effect. A preference for lower mantle viscosities >1022 Pa s is found, in which case at least 60% of the observed long‐wavelength gravity anomaly can be attributed to GIA. This lower bound on the lower mantle viscosity has implications for inferences based on models for mantle convection and GIA.

Subject

glacial isostatic adjustment
gravity modeling
Hudson Bay
mantle viscosity

To reference this document use:

http://resolver.tudelft.nl/uuid:9f5a51cd-61b6-4866-8dfd-d8f634292401

DOI

https://doi.org/10.1029/2020JB020484

ISSN

2169-9313

Source

JGR Solid Earth, 125 (12)

Part of collection

Institutional Repository