Probing the Western Antarctic Lithosphere and Asthenosphere with New Approaches to Imaging Seismic Wave Attenuation and Velocity

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The western portion of the Antarctic continent is very active in terms of plate tectonic processes that can produce significant variations in the Earths mantle temperature as well as partial melting of the mantle. In addition to these internal processes, the ice sheet in western Antarctica is melting due to Earths warming climate and adding water to the ocean. These changes in ice mass cause adjustments in rocks within the Earth's crust, allowing the surface to rebound in some locations and fall in others, altering the geographical pattern of sea-level change. However, the solid Earth response depends strongly on the strength of the rocks at a wide range of timescales which is not well-known and varies with temperature and other rock properties. This project has three primary goals. (1) It will assess how processes such as rifting, mantle upwelling and lithospheric instability have altered the lithosphere and underlying asthenosphere of western Antarctica, contributing to a planet-wide understanding of these processes. (2) It will use new measurements of mantle and crust properties to estimate the rate at which heat from the solid Earth flows into the base of the ice, which is important for modeling the rates at which the ice melts and flows. (3) It will places bounds on mantle viscosity, which is key for modeling the interaction of the solid Earth with changing ice and water masses and their implications for sea-level rise. To accomplish these goals, new resolution of crust and mantle structure will be obtained by analyzing seismic waves from distant earthquakes that have been recorded at numerous seismic stations in Antarctica. These analyses will include new combinations of seismic wave data that provide complementary information about mantle temperature, heat flow and viscosity. This project will provide educational and career opportunities to a Brown University graduate student, undergraduates from groups underrepresented in science who will come to Brown University for a summer research program, and other undergraduates. The project will bring together faculty and students for a seminar at Brown that explores the connections between the solid Earth and ice processes in Antarctica. Project research will be incorporated in outreach to local public elementary schools and high schools. This research addresses key questions about mantle processes and properties in western Antarctica. What are the relative impacts of rifting, mantle plumes, and lithospheric delamination in the evolution of the lithosphere and asthenosphere? Where is topography isostatically compensated, and where are dynamic processes such as plate flexure or tractions from 3-D mantle flow required? What are the bounds on heat flow and mantle viscosity, which represent important inputs to models of ice sheet evolution and its feedback from the solid Earth? To address these questions, this project will measure mantle and crust properties using seismic tools that have not yet been applied in Antarctica: regional-scale measurement of mantle attenuation from surface waves; Sp body wave phases to image mantle velocity gradients such as the lithosphere-asthenosphere boundary; and surface wave amplification and ellipticity. The resulting models of seismic attenuation and velocity will be jointly interpreted to shed new light on temperature, bulk composition, volatile content, and partial melt, using a range of laboratory-derived constitutive laws, while considering data from mantle xenoliths. To test the relative roles of rifting, mantle plumes, and delamination, and to assess isostatic support for Antarctic topography, the predictions of these processes will be compared to the new models of crust and mantle properties. To improve bounds on western Antarctic heat flow, seismic attenuation and velocity will be used in empirical comparisons and in direct modeling of vertical temperature gradients. To better measure mantle viscosity at the timescales of glacial isostatic adjustment, frequency-dependent viscosity will be estimated from the inferred mantle conditions. This project will contribute to the education and career development of the following: a Brown University Ph.D. student, Brown undergraduates, and undergraduates from outside the university will be involved through the Department of Earth, Environmental and Planetary Sciences (DEEPS) Leadership Alliance NSF Research Experience for Undergraduates (REU) Site which focuses on geoscience summer research experiences for underrepresented students. The project will be the basis for a seminar at Brown that explores the connections between the solid Earth and cryosphere in Antarctica and will contribute to outreach in local public elementary and high schools.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.