Geodesy in Antarctica

GPS measurement of isostatic rebound and tectonic deformation in Marie Byrd Land, West Antarctica

Three autonomous Global Positioning System (GPS) stations were installed in Marie Byrd Land, West Antarctica to measure glacio-isostatic rebound and tectonic deformation. Antarctica is an important, but poorly understood piece in the global tectonics puzzle. It is widely accepted that active deformation is ongoing in western Marie Byrd Land (wMBL) and the Ross Embayment. These are both part of the West Antarctic Rift System, but rates and causes of the deformation are unknown. Two possible causes of the deformation observed in this region include tectonic extension in the Ross Embayment as West and East Antarctica separate and crustal uplift caused by isostatic rebound following the last glacial maximum.

The type and magnitude of deformation in this region has serious implications both for global tectonic interpretations and ice sheet models. If active extension is occurring in the Embayment, this could affect interpretations of the global plate tectonic model, depending on its magnitude. Knowing the rate could also aid in improving our understanding of the extension occurring in the Embayment as well as the uplift history of the Transantarctic Mountains. Determining the uplift rates due to post glacial rebound will help to determine the timing and configuration of the ice sheet during the Last Glacial Maximum, and may help to determine whether the ice sheet collapsed during the mid-Holocene, about 6000 years ago.

In order to measure the ongoing deformation in wMBL, we have installed three continuously recording, autonomous GPS stations on outcrops in wMBL with baselines of ~100-200 km. The stations will gather data for at least four years, and are being installed in concert with a series of autonomous stations in the Transantarctic Mountains, resulting in an unprecedented long baseline array across the Ross Embayment.

Nunatak east of Mount Carbone, Phillips Mountains, western Marie Byrd Land

The remote GPS stations are powered by a combination of batteries, solar panels, and a wind generator. A series of regulators control the power system, and data is stored on a serial data recorder as well as in the GPS receiver at each station. Data is downloaded once or twice each year to acquire up to 12 months of coverage per year. The data collected will be later processed and will allow us to determine the crustal motions to an accuracy of 1 mm/yr horizontal and 2 mm/yr vertical. The array will also detect horizontal strain gradients in wMBL, and combined with strain data from the Transantarctic Mountains, will allow us to construct models for tectonic extension and postglacial rebound.

This project is joint between Bruce Luyendyk of the University of California, Santa Barbara and Andrea Donnellan, Carol Raymond and Erik Ivins of the Jet Propulsion Laboratory, and brings together experts in wMBL geology and tectonics, tectonic geodesy, and lithospheric deformation. Funding is from the National Science Foundation Office of Polar Programs and NASA.

Autonomous GPS in the Transantarctic Mountains

Recent modeling of the lithospheric response to glacial loading and unloading has shown that the Antarctic lithosphere is likely to exhibit a strong memory of Pleistocene-Holocene deglaciation due to viscoelastic deformation of the lithosphere. Other parameter studies reveal the importance of crustal rheology - lithospheric thickness and mantle viscosity - in determining the response of the lithosphere to more recent glacial cycles. These results provide a template for designing geodetic observation strategies to constrain the past and present state of the West Antarctic Ice Sheet (WAIS), and for interpreting those observations.

Geodetic methods to monitor the mass balance of the Antarctic Ice Sheet include high-precision Global Positioning System (GPS) measurements of horizontal and vertical deformation of the lithosphere, and high-precision measurements of time-varying gravity, from land-based absolute gravity and satellite gravity mapping. Permanent GPS sites on bedrock exist at only a handful of stations around the periphery of the continent, as part of the International GPS Service. To complement these sites, we have initiated implementation of a GPS array in the Transantarctic Mountains (TM), which will provide data to test competing scenarios for the melting history of the Antarctic Ice Sheet since Last Glacial Maximum.

Mount Cocks GPS station, Transantarctic Mountains

A parameter study of late Holocene ice fluctuations demonstrates that crustal deformation due to these younger surface mass changes is quite sensitive to both the lithospheric thickness and mantle viscosity. In view of the tectonic and magmatic history, and the ongoing rifting and volcanism in West Antarctica, it is clear that more sophisticated models of the Antarctic lithosphere may be necessary to understand geodetic observations. Advances in modeling the lithospheric response to deglaciation, and availability of high quality GPS observations will lay the foundation for a real-time monitoring of the mass balance of the WAIS along with GRACE and GLAS.

Read the Autonomous Systems in Extreme Environments (ASEE) Workshop Final Report. [PDF]