GPS Measurements of Crustal Motion Indicate 3D GIA Models are Needed to Understand Antarctic Ice Mass Change

Friday, 19 December 2014
Stephanie Ann Konfal1, Terry J Wilson1, Michael G Bevis1, Eric C Kendrick1, Ian W D Dalziel2, Robert Smalley Jr3, Michael J Willis4, David Heeszel5 and Douglas A Wiens6, (1)Ohio State University, Columbus, OH, United States, (2)University of Texas at Austin, Institute for Geophysics, Austin, TX, United States, (3)Univ Memphis, Memphis, TN, United States, (4)Cornell University, Ithaca, NY, United States, (5)Nuclear Regulatory Commission, Washington, DC, United States, (6)Washington University in St Louis, Department of Earth and Planetary Sciences, St. Louis, MO, United States
Continuous GPS measurements of bedrock crustal motions in response to GIA in Antarctica have been acquired by the Antarctic Network (ANET) component of the Polar Earth Observing Network (POLENET). Patterns of vertical crustal displacements are commonly considered the key fingerprints of GIA, with maximum uplift marking the position of former ice load centers. However, efforts to develop more realistic 3D earth models have shown that the horizontal motion pattern is a more important signature of GIA on a laterally varying earth. Here we provide the first measurements substantiating predictions of a reversal of horizontal motions across an extreme gradient in crustal thickness and mantle viscosity crossing Antarctica. GPS results document motion toward, rather than away from the sites of major ice mass loss in West Antarctica. When compared in a common reference frame, observed crustal motions are not in agreement with predictions from models of GIA. A gradient in crustal velocities, faster toward West Antarctica, is spatially coincident with the rheological boundary mapped from seismic tomographic results. This suggests that horizontal crustal motions are strongly influenced by laterally-varying earth properties, and demonstrates that only 3D earth models can produce reliable predictions of GIA for Antarctica.