Research Objectives:
We will investigate the new-found, startling sensitivity of major west antarctic ice streams to tidal oscillations in order to learn the extent and character of the effect and its ramifications. Ice streams D, C, and Whillans (B) all show strong but distinct tidal signals. The ice plain of Whillans is usually stopped outright, forward motion being limited to two brief periods a day, at high tide and on the falling tide. Motion propagates across the ice plain at seismic wave velocities. Near the mouth of D, tides cause a diurnal variation of about 50 percent in ice-stream speed that propagates upglacier more slowly than on Whillans, and seismic data show that C experiences even slower upglacier propagation of signals. Tidal influences are observed more than 100 kilometers (km) upglacier on C and more than 40 km upglacier on D and may be responsible for fluctuations in basal water pressure reported 400 km upstream on Whillans.
During the first year, five coordinated seismic and global positioning system (GPS) instrument packages placed 100 kilometers apart on each stream will measure Whillans and ice stream D. These packages will be deployed at sites selected by satellite imagery and will operate autonomously for two lunar cycles to study the sensitivity of the streams to spring and neap tides. Also, we will examine existing data sets for clues to the mechanisms involved and develop preliminary models.
During the second and third seasons, we will examine in greater detail the tidal behavior of Whillans and D. We will especially focus on at least one source area for Whillans, assuming that areas inferred from preliminary data remain active. Vertical motions have not yet been detected, but differential GPS will increase sensitivity. Seismic instrumentation will greatly increase temporal resolution and the ability to measure the propagation speed and any spatial heterogeneity.
Improved knowledge of ice-stream behavior will contribute to assessing the potential for rapid ice-sheet change affecting global sea levels. Results will be disseminated through scientific publications and talks at professional meetings, as well as contacts with the press, university classes, visits to schools and community groups, and other activities.
