Tidal Modulation of Ice Stream Motion

3-104 3-105 Investigation of the recently discovered phenomenon that the motion of major West Antarctic ice streams is modulated strongly by forces that vary with tidal oscillations of the ice shelf was based largely on the capabilities of GPS receivers and the availability of a large number of such receivers from UNAVCO. During the 2003-04 field season, 15 UNAVCO receivers along with some owned by Penn State and the University of New Hampshire were deployed among all the ice streams draining in to the Ross Ice Shelf. These receivers were deployed to determine the nature of the modulation and the along-stream strength of the sensitivity. The UNAVCO receivers included a number of older Trimble 4000’s that required external storage to meet our scientific requirements, but UNAVCO was extremely helpful in providing expertise both in the continental U.S. (CONUS) and in McMurdo to ensure that the systems worked reliably. Whillans Ice Stream was the only ice stream that exhibited stick-slip motion, although the fraction of motion occurring during slips decreased upstream to below50% at a distance 100 km from the grounding line. On the Tidal Modulation of Ice Stream Motion