Australia: The Land Where Time Began

A biography of the Australian continent 

Antarctica - The West Antarctic Ice Sheet - WAIS

Most of the WAIS, a marine ice sheet, is grounded at more than 1 km below sea level, and in the Byrd Subglacial Basin, at more than 2 km below sea level. A series of rapidly flowing ice streams are formed as the drainage from the WAIS is predominantly convergent towards the coast. Most of the ice that flows from the WAIS is accounted for by these ice streams (Hughes, 1973; Goldstein, Engelhardt, Kamb & Fröhlich, 1993; Williams, Jackson & Tseng, 1993). All of the ice sheet flow processes - internal deformation, basal sliding, and deformation of the bed the ice stream rests upon - are active.

It has been shown by studies of the Ross Sea region that different ice streams flow at different rates and have different mass balances, and physical behaviour (Shabtaie & Bentley, 1987; Alley & Williams, 1991; Jacobel & Bindschadler, 1993). At the present [1999] Ice Stream C is inactive (Shabtaie & Bentley, 1987) but the adjacent Ice Stream B is flowing at several hundred km/yr (Bindschadler et al., 1987; Williams et al., 1993). It has been suggested a major portion of the drainage of Ice Stream C being captured by another ice stream (Rose, 1979), the capture by Ice Stream B of the basal water from Ice Stream C, the removal of the deforming bed of Ice Stream C, or a combination of these factors (Alley, pers. comm. to the author¹) may have led to the inactivity of Ice Stream C.

 It is believed the bed beneath the ice streams divides and thaws, as the frictional heat is stronger near the ice stream centres and lower where streams divide (Hughes, 1981). Fast-flowing ice streams are separated from adjacent ice streams that are flowing more slowly by distinct shear zones with an average width of 5 km. Bands of crevasses that are oriented transverse to flow are the ice surface manifestation of these zones (Shabtaie & Bentley, 1982; Bindschadler et al., 1987).

Compared to that of its counterpart in East Antarctica the surface profile of the WAIS is gentle, indicating that the rate of flow and ablation is higher than that of the East Antarctic Ice Sheet (EAIS), which supports models that are based on basal sliding and "wet-based" conditions for the WAIS (Hughes, 1973, 1977 and 1981). Uncertainty remain as to the exact meltwater nature at the base of the WAIS, whether it occurs as a thin film centimetres thick that spreads under the immense hydrostatic pressure at the base of the ice sheet (Weertman, 1972), or if there are channelised water systems beneath the ice sheet (Hughes, 1981). An alternative suggestion is that the meltwater may be incorporated into the sedimentary bed beneath the ice sheet (Boulton & Jones, 1979; Alley et al., 1989; Engelhardt et al., 1990). As these issues bear on the mechanism of the sliding of ice sheets, and ultimately the stability of the ice sheets, they are important (Hughes, 1981).

Examination of geomorphic features and subglacial sediments on the continental shelf, products of the most recent glacial maximum, determines the relationship between the ice sheet, ice streams, sea level, climate and the ice sheet bed.

Sources & Further reading

1. Anderson, John B., 1999, Antarctic Marine Geology, Cambridge University Press