Influence of ice loading and earth properties on horizontal GPS motions in the Ross Sea region, Antarctica

ANET-POLENET (Antarctic Network of the Polar Earth Observing Network) bedrock GPS sites in the Ross Sea region of Antarctica are in close proximity to a major LGM load center in the Siple region, and therefore are thought to reflect motion due to GIA. For the simplest case, horizontal bedrock motion is expected in a radial pattern away from the former load, yet we instead observe three primary patterns of deformation; 1) motions are reversed towards the load in the southern region of the Transantarctic Mountains (TAM), 2) motions are radially away from the load in the Marie Byrd Land (MBL) region, and 3) an overall gradient in motion is present, with magnitudes progressively increasing from East to West Antarctica. We aim to understand these distinct patterns of horizontal bedrock motion and the causal sources of deformation by investigating alternative earth models and ice loading scenarios, with the goal of improving our understanding of GIA and ice mass change in Antarctica. We explore ice loading scenarios for the Wilkes Subglacial Basin (LGM time scale) and the Siple Coast (centennial and millennial time scales), using GIA models with 1D earth models. We find that the spatial extent of deformation resulting from Wilkes and Siple loading is significant, but that no 1D model, regardless of the earth model and ice loading scenario used, is able to reproduce all three distinct patterns of observed motion at the same time. For select loading scenarios, we also examine 3D GIA models by invoking a boundary in Earth properties beneath the Transantarctic Mountains. This approach accounts for the strong lateral gradient in earth properties across the continent by effectively separating East and West Antarctica into two different earth model profiles. Some of our GIA models utilizing 3D earth structure are able to reproduce predicted motions that directionally match all three observed patterns of deformation. Best fitting ice history and earth models are presented, including preferred upper mantle viscosity values.