Reevaluating the Elastic Response to Ice Mass Change in Antarctica

Abstract:

The instantaneous elastic response of the Earth to present-day changes in ice mass is superimposed on the Earth’s viscous response to the integrated history of past ice mass changes. In regions such as the northern Antarctic Peninsula and the Amundsen Sea Embayment, elastic uplift rates at the GNSS receivers reach up to 7-10 mm/yr, or up to~30-45% of the observed uplift rate. In glacial isostatic adjustment studies, this elastic response is often modeled and removed from the observed deformation using a 1D depiction of the Earth with elastic parameters described by a global reference. The viscous component, inferred to be the residual, is used for constraining mantle rheology. The uncertainties and biases in modeled elastic deformation remain poorly understood but directly impact the amount of inferred viscous deformation and estimates of Antarctic mantle viscosity. We quantify these uncertainties using an ensemble of 1D elastic structures sampled from density and seismic velocity models of Antarctica’s crust and upper mantle with a combination of 5-10 km resolution continent-wide ice mass balance estimates and new, high resolution ice mass balance estimates of the Amundsen Sea region. Our results show that the largest source of uncertainty (i.e., the spread of the ensemble of elastic deformation) comes from the propagation of uncertainties in the density of the firn/ice load, which are ~15% or less of the elastic uplift rate for 75% of Antarctic GNSS sites. Uncertainties that result from treating the elastic properties of the Earth as radially symmetric are much smaller at less than 4% of the modeled elastic uplift rate for 75% of Antarctic GNSS sites. Our new quantified uncertainties allow for inter comparison of modeled elastic deformation rates from different studies for the first time and will help inform future studies for furthering the state of the art of probing the Antarctic mantle rheology.