Research Objectives:
Motion in the bedrock that underlies the West Antarctic Ice Sheet is suspected from rifting, active volcanism and uncertainties in global plate circuits, but it is unconstrained. Without reliable data - on both tectonic and ice-induced crustal motions-we will never be able to fully comprehend the ice sheet's past, present, and future dynamics. Without that knowledge, we can neither develop reliable global change scenarios for the future nor accurately factor the Antarctic region into global plate movements. Currently, permanent global positioning system (GPS) networks that measure bedrock movement are established only on the fringe of the West Antarctic Ice Sheet; they cannot provide the data that are needed for understanding of subglacial volcanism, active tectonics, and ice streaming.
This project is focused on establishing baseline, long-term, reliable geodetic measurements of the crustal motion in the bedrock beneath the West Antarctic Ice Sheet. To obtain them, we are building a West Antarctica GPS Network (WAGN) of at least 15 GPS sites on nunataks across the West Antarctic interior-an area comparable to the area from the Rocky Mountains to the Pacific coast-over 3 years, beginning in the 2001-2002 austral summer.
The first season, we initiated the WAGN network and tested the precision and velocities at critical control sites along the interior Transantarctic margin of the East Antarctic craton. The second season we monumented and made initial measurements on sites at the base of the Antarctic Peninsula, and on the Ellsworth-Whitmore mountains crustal block. The embryonic network will begin to fill a major gap in GPS coverage by looking for potential bedrock movements. If crustal motions are relatively slow, meaningful results will only begin to emerge over the next 5 years or so. Once it is permanently established, however, the network should yield increasingly meaningful results. Indeed, the slower the rates turn out to be, the more important it is to start measuring early.
West Antarctic Ice Sheet bedrock is so scattered and remote that to erect a continuous string of permanent GPS stations is unrealistic with presently available technology and logistic support. Instead, we are following the ''multimodal occupation strategy' (MOST), which entails roving receivers (based in permanent monuments set in solid rock outcrops) in place for only a short time at each site, providing data that can be ranged against continuous data acquired from permanent GPS stations elsewhere. Each of these "bases" can be converted in the future to a permanent, autonomous station when more logistics and satellite data linkage throughout West Antarctica are in place. When detectable motions occur, we can reoccupy the most critical sites, obtain more reliable velocities, and make decisions about reoccupying the entire network.
We expect the results of this project to establish important early indicators of crustal plate dynamics beneath the West Antarctic Ice Sheet. As scientists take these into account in refining their models, future measurements and a time-series of the geodetic data should gradually produce a more constrained picture of subglacial dynamics for the West Antarctic Ice Sheet-that is, plate rotations and both elastic and viscoelastic motions caused by deglaciation and ice-mass changes.
