RISS, RISP and RIGGS: Post-IGY glaciological investigations of the Ross Ice Shelfin the U.S. programme

Abstract

Abstract Geophysical and glaciological data compiled since the IGY have led to a new picture of ice shelf dynamics, so that the ice shelf is now viewed as a dynamic system that responds strongly to changes in ice input and grounding line fluctuations, and that may be crucial to the existence of the inland ice sheet. Measurements over the last twenty years have revealed the following characteristics about the shelf. Sonic logging in a drill hole in the ice demonstrates a striking anomaly in wave velocity that may be associated with the passage of the ice over the grounding line. Seismic shear wave velocities show anisotropic characteristics that may reflect either crystal anisotropy or stress anisotropy, or both. The apparent dielectric constant in the ice is significantly less than expected from laboratory studies and may exhibit real regional variations. The mass output from the ice shelf is only about half as great as the glacier input through the Transantarctic Mountains plus the surface accumulation on the shelfand its West Antarctic drainage basin, yet measurements on the ice shelf indicate that the mass balance is near zero. This could be consistent with recovery from a past surge of the West Antarctic inland ice. The submarine topography is dominated by broad ridges and valleys extending in an unbroken pattern from the open Ross Sea past the Ross Ice Shelf to the grid eastern part of the West Antarctic inland ice. Convolutions in the ice thickness suggest turbulent flow. Detailed examination of thickness variations, of present-day ice movement rates, of the record of past flow lines revealed by radar soundings, and of isostatic gravity anomalies has led to a picture of Holocene retreat and fluctuations in grounding line positions during the last 1500 years.