Glaciological studies on Rutford Ice Stream, Antarctica

Abstract

Rutford Ice Stream drains part of the West Antarctic ice sheet into Ronne Ice Shelf. Much of the drainage basin has a bed well below sea level and is therefore an area which could undergo substantial change if a climatic warming were to cause sustained thinning of Ronne Ice Shelf. Snow accumulation data suggest that an accumulation rate of 0.51 + 0.12 Mg m -2 yr -• is required for balance. An extensive ice movement survey network was established across the grounding line in 1978-1980 and was extended for more than 100 km upstream in 1984-1986. Velocities at five sites have been calculated using doppler satellite position measurements. When the velocities are combined with cross-sectional areas of the ice stream measured by radio echo sounding, mass flux figures show that drag at the sidewalls and on the base must decrease downstream toward the grounding line. The increasing influence of buoyancy forces on ice stream motion is also shown by the steady rise in the ratio of bedrock depth to ice thickness going downstream along the network. Below the grounding line that was found to cross the middle part of the earlier network is a zone stretching for a further 100 km where it can now be shown that the ice stream is intermittently grounded. In these grounded areas the glacier bed is raised with respect to the surrounding seabed and forms eskerlike features. Surface elevations over the grounded areas are less than 30 m above those needed for hydrostatic equilibrium. ß ©©©© © ß ß ß ß ß ß ß ß 0 t t f DIs•nce (kin) ß 150 (b) 09 O8 07 ß ©©©© ß ß ,lee ß ß ß ©© ß ß ß ß ß ß ß ß ee ©©e e ß ß t t t t 0 _ ß ß ß ß ß ß el ß ß eeeeee +5OOl o •-1000 -2000 =2000 + • ee eee. e. ß ß eeeee ee ß ß ß .e ß ee ß ß ß ß .! el • • ß ß ß e ß '' I e • Dish•nce (km)

Rapid erosion, drumlin formation, and changing hydrology beneath an Antarctic ice stream

“…Bed slopes need to be more than nine times greater than those at the surface to be more effective at controlling the fl ow of subglacial water. The maximum bed slope in the region of our seismic surveys is >10°, whereas surface slopes are <0.01° (Doake et al, 1987), so the motion of any free water under high pressure at the ice-bed interface will be controlled by the bed, rather than by the surface. Hence, we expect any signifi cant quantities of free water to occur in the deeper parts of the bed and not where the erosion occurred (Smith, 1997).…”

Ice stream or not? Radio-echo sounding of Carlson Inlet, West Antarctica

“…Treating the approximate length of an ice stream as the along-flow distance between the onset of fast flow (>100 m a −1 ) and the grounding line Rutford Ice Stream is 240 km long. The flow speed in the main trunk is 300-400 m a −1 (Doake et al, 1987;Frolich et al, 1989).…”

“…Like Rutford Ice Stream, Carlson Inlet lies in a deep, linear trough (Fig. 1b) (Doake et al, 1987). The ice in Carlson Inlet is between 1700 and 2000 m thick with the deepest parts adjacent to Kealey Ice Rise.…”

Insights into ice stream dynamics through modelling their response to tidal forcing

“…Initial measurements of tidal forcing on ice were limited to the surface of the ice shelves (Williams and Robinson, 1980) and the hinging zone where ice flexure occurs near the grounding line (Smith, 1991;Doake et al, 1987). In these regions, tidal effects can be simply described with analytical solutions and elastic beam theory (Holdsworth, 1969(Holdsworth, , 1977Reeh et al, 2003).…”