Abstract
AbstractGlacial‐isostatic adjustment (GIA) is the key process controlling relative sea‐level (RSL) and paleo‐topography. The viscoelastic response of the solid Earth is controlled by its viscosity structure. Therefore, the appropriate choice of Earth structure for GIA models is still an important area of research in geodynamics. We construct 18 3D Earth structures that are derived from seismic tomography models and are geodynamically constrained. We consider uncertainties in 3D viscosity structures that arise from variations in the conversion from seismic velocity to temperature variations (factor r) and radial viscosity profiles (RVP). We apply these Earth models to a 3D GIA model, VILMA, to investigate the influence of such structure on RSL predictions. The variabilities in 3D Earth structures and RSL predictions are investigated for globally distributed sites and applied for comparisons with regional 1D models for ice center (North America, Antarctica) and peripheral regions (Central Oregon Coast, San Jorge Gulf). The results from 1D and 3D models reveal substantial influence of lateral viscosity variations on RSL. Depending on time and location, the influence of factor r and/or RVP can be reverse, for example, the same RVP causes lowest RSL in Churchill and largest RSL in Oregon. Regional 1D models representing the structure beneath the ice and 3D models show similar influence of factor r and RVP on RSL prediction. This is not the case for regional 1D models representing the structure beneath peripheral regions indicating the dependence on the 3D Earth structure. The 3D Earth structures of this study are made available.
Highlights
During the last glacial maximum (LGM), at around 21,000 years before present, large ice sheets covered North America, northern Eurasia, Antarctica, Greenland, and Patagonia, while the global mean sea-level was ∼130 m lower than present (e.g., Lambeck et al, 2014)
To investigate the impact of lateral variability in mantle viscosity on relative sea-level (RSL) predictions, we considered 3D viscosity structures derived from seismic-tomography models and constrained by the geoid, the heat flux and mineral physics data from which a temperature distribution was derived
Different mean radial viscosity profiles (RVP) were considered, which resulted in viscosity varying by a factor of four and lithospheric thickness varying by tens of km
Summary
During the last glacial maximum (LGM), at around 21,000 years before present (ka BP), large ice sheets covered North America, northern Eurasia, Antarctica, Greenland, and Patagonia, while the global mean sea-level was ∼130 m lower than present (e.g., Lambeck et al, 2014). Global GIA models predict the solid-Earth deformation and the change in relative sea-level (RSL) due to the loading induced by mass redistribution between ice and water. They include the change in the gravity. Yousefi et al (2018, 2021) focused on the Pacific coast of central North America They combined 29 ice-sheet reconstructions and more than 700 1D Earth structures to set up a large ensemble, but failed to achieve an acceptable fit to a global set of RSL data with a single set of model parameters, suggesting a requirement for a more complex Earth structure. We focus on ice center (North America, Antarctica) and peripheral regions (Central Oregon Coast, San Jorge Gulf) to investigate the effect of regionally adapted 1D structures (Section 4)
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