Global Glacial Isostatic Adjustment Constrained by GPS Measurements: Spherical Harmonic Analyses of Uplifts and Geopotential Variations

Yan Zhou,Jiancheng Li,Jiesi Luo,Yong Huang,Jim Ray,Shaomin Yang

doi:10.3390/rs12071209

Abstract

In addition to studies of sea level change and mantle rheology, reliable Glacial Isostatic Adjustment (GIA) models are necessary as a background model to correct the widely used Gravity Recovery and Climate Experiment (GRACE) monthly gravity solutions to determine subsecular, nonviscous variations. Based on spherical harmonic analyses, we developed a method using degree-dependent weighting to assimilate the Global Positioning System (GPS) derived crustal uplift rates into GIA model predictions, in which the good global pattern of GIA model predictions and better local resolution of GPS solutions are both retained. Some systematic errors in global GPS uplift rates were also corrected during the spherical harmonic analyses. Further, we used the refined GIA uplift rates to infer the GIA-induced rates of Stokes coefficients (complete to degree/order 120) relying on the accurate relationship between GIA vertical surface deformation and gravitational potential changes. The results show notable improvements relative to GIA model outputs, and may serve as a GIA-correction model for GRACE time-variable gravity data.

Highlights

During the last glacial maximal (~18,000 years ago), large portions of the Northern and Southern Hemispheres were covered with great sheets of ice, which caused isostatic depressions of the land below and around the ice but bulges surrounding these indentations
We developed a method to combine and refine the crust uplift rates derived from Glacial Isostatic Adjustment (GIA) models and GPSinterp ICE6Gavg (GPS) observations, since GPS uplifts can be very good in some small regions but are very poor in global patterns, especially for the global systematic errors evidenced as the surface uplifting of the whole Earth, and the GIA model is on the contrary
Our results absorbed the merits from both GIA models and GPS data, and removed the systematic errors in the global GPS crustal uplift rates

Summary

Introduction

During the last glacial maximal (~18,000 years ago), large portions of the Northern and Southern Hemispheres were covered with great sheets of ice, which caused isostatic depressions of the land below and around the ice but bulges surrounding these indentations. Though the ice retreated long ago, much of North America, Scandinavia, Greenland, and Antarctica are still rising where the massive layers of ice pushed it down, while the bulges are still slowly sinking. This ongoing movement of land is a viscous response to its ice-age burden and is called the Glacial Isostatic Adjustment (GIA). The GIA-induced vertical crustal deformations, or crust uplifts, cause mass redistributions within the Earth and lead to changes in geopotential. On decadal and shorter time scales, GIA-induced changes in geopotential and crustal uplift can both be regarded as linear drifts. GIA ≡ ∂uGIA(θ, λ, t)/∂t and rate of geopotential change

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