Mantle Viscosity Derived From Geoid and Different Land Uplift Data in Greenland

The Earth's mass redistribution due to deglaciation and recent ice sheet melting causes changes in the Earth's gravity field and vertical land motion in Greenland. The changes are because of ongoing mass redistribution and related elastic (on a short time scale) and viscoelastic (on time scales of a few thousands of years) responses. These signatures can be used to determine the mantle viscosity. In this study, we infer the mantle viscosity associated with the glacial isostatic adjustment (GIA) and long‐wavelength geoid beneath the Greenland lithosphere. The viscosity is determined based on a spatio‐spectral analysis of the Earth's gravity field and the land uplift rate in order to find the GIA‐related gravity field. We used different land uplift data, that is, the vertical land motions obtained by the Greenland Global Positioning System (GPS) Network (GNET), gravity recovery and climate experiment (GRACE) and glacial isostatic adjustment (GIA) data, and also combined them using the Kalman filtering technique. Using different land uplift rates, one can obtain different GIA‐related gravity fields. As shown in this study, the mantle viscosities of 1.9 × 1022 Pa s and 7.8 × 1021 Pa s for a depth of 200–700 km are obtained using ICE‐6G (VM5a) model and the combined land uplift model, respectively, and the GIA‐related gravity potential signal. Plain Language Summary The Earth is not a rigid object and has different dynamic changes that shape its mantle and surface. The heat of the Earth's core results in mantle flow, generating global mantle convection. The pressure of these flows pushes or pull the surface away from its isostatic equilibrium. Computing these stresses helps us have a better vertical land motion model for the Earth's surface. Another dynamic process that is important to include is glacial isostatic adjustment (GIA), an important issue for example, for the sea‐level rise studies. The Earth's surface has not yet reached its equilibrium state due to the presence of huge ice sheets in the last 25,000 years. This crustal land uplift needs to be identified and modeled well. A gravimetric land uplift model was developed based on satellite gravity missions (GRACE recovery and climate experiment) and compared with the one obtained from the Global Positioning System data and geophysical models in this study. These data were used for determining the mantle viscosity in Greenland. The mantle viscosity models help us understand the mantle's mechanical behavi