Ice dynamics at the mouth of ice stream B, Antarctica

Abstract

Field data collected at the mouth of Ice Stream B show that the flow dynamics of this region are distinctly different than either the major portion of the ice stream upstream or the ice shelf downstream. Surface slopes in this region are as low as ice shelf surface slopes, yet with the exception of patches of ice which may be floating, the ice is grounded. Basal shear stress is negligible, the resistance to flow being partitioned between shear at the sides and longitudinal gradients of longitudinal and transverse stress. The surface is generally crevasse-free. Features similar to ice rises are observed upstream of the grounding line. Their origin is uncertain, but they move at velocities comparable to the surrounding ice. The flow is laterally extensive and longitudinally compressive, but there are large local variations of the strain rate from the regional trends. The boundary between the two major tributaries to Ice Stream B, followed with the radar, is characterized by a band of strain rates much smaller than average. Detailed measurements at the downstream B network highlight this local variability of strain rates but confirm that there is a strong correlation between surface topography and strain rates. The strain rates indicate that the undulating topography is locally generated. The lower-elevation ice is thicker and moves faster. A velocity profile across the crevassed northern margin shows that the decrease of velocity toward the edge is nearly linear. A calculation of ice stream discharge at this location agrees closely with two rather rough estimates of balance flux and is considerably larger than a third estimate. The discharge of Ice Stream B does not appear to be significantly out of balance with published estimates of total ice accumulation within the present catchment basin. rather ad hoc assumptions. Therefore the results of such models must be viewed with a very cautious eye.Presented in this paper are data collected in the region of the mouth of Ice Stream B, West Antarctica, during three field seasons (1983-1984 through 1985-1986). These data provide an excellent opportunity for understanding the ice flow in the mouth of an active ice stream as well as the interaction of ice

Ocean Tide Influences on the Antarctic and Greenland Ice Sheets

“…The link between surface strand cracks and tidal flexure, and their opening and closing with the ocean tides, led to the use of observations of surface strand cracks (typically 0.001 to 0.01 m wide and extending for kilometers) to identify or confirm the position of the grounding line for some ice shelves (e.g., Bindschadler, 1993;Bindschadler et al, 1987;Horgan & Anandakrishnan, 2006;Thomas et al, 1988).…”

Geomorphology under ice streams: Moving from form to process

“…Alley (1993) suggested that Ice raft 'a' (an elliptical feature 10 km by 5 km and a few metres high, near the mouth of Ice Stream B: cf. Bindschadler et al, 1987), might be an obvious candidate for this type of sticky spot. Elsewhere, under Ice Stream C, it was suggested that areas of well drained ('stickier') till of the order of 10 2 m 2 generated micro-earthquakes (Anandakrishnan and Bentley, 1993;Anandakrishnan and Alley, 1994).…”

Variable deceleration of Whillans Ice Stream, West Antarctica

“…The longest time series is available at stake M0 (1963 to 2011) due to an average velocity determined from feature tracking between 1963 DISP and 1997 RADARSat [ Joughin et al , ]. The greatest rate of change reported by Joughin et al [] most closely matches observations made at F7 in the 1970s [ Thomas et al , ] and at M0 in the 1980s [ Bindschadler et al , ; Whillans et al , ]. Although F7 and M0 are nearly 50 km apart, the difference in velocities, as estimated from InSAR data sets, is less than 4 m/yr, considerably smaller than the uncertainty in these earlier observations (± 25 m/yr) [ Bindschadler et al , ].…”