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Assessing the role of subglacial hydrology on the flow of West Antarctic ice streams: a numerical modelling approach

Assessing the role of subglacial hydrology on the flow of West Antarctic ice streams: a numerical modelling approach

The West Antarctic ice sheet is a marine ice sheet with a bed that lies largely below sea level. It is potentially unstable, and there is a possibility that ice from the interior of the ice sheet may suddenly discharge to the ocean leading to rises in global sea level. Most of the present ice discharge occurs in fast moving ice streams. An understanding of the dynamics of these ice streams is crucial if we are to predict the future evolution of the ice sheet and its effect on global sea level.

The most studied ice streams in West Antarctica are those located along the Siple Coast, comprising six major ice streams separated by a series of ice ridges (Figure 1). These ice streams exhibit a century-scale variability in ice discharge and flow direction, that has a strong control on the mass balance on the West Antarctic ice sheet. It is known that a subglacial water system plays an important role in the form and flow velocity of these ice streams, but the exact nature of the hydrological system is still a matter of debate.

This research is based on the development and testing of a subglacial hydrological model for the West Antarctic ice streams. This modelling initiative is motivated by new findings showing rapid movement of water stored in lakes beneath the Siple Coast ice streams (Grae et al., 2005; Fricker et al., 2007). To ascertain the role that changes in subglacial hydrology and water storage play on the flow of Antarctic ice streams, I intend to couple the hydrological model with an existing ice stream model (Bougamont et al., 2003a, b). The coupled model will be applied to the stagnant Ice Stream C (Kamb Ice Stream) and the fast flowing Ice Stream B (Whillans Ice Stream). Observations show that the subglacial hydrological system beneath these glaciers may exert an important control on their motion. Water is observed to accumulate behind the trunk of Ice Stream C, which stopped approximately 150 years ago, causing an ice bulge to advance progressively (Vogel et al., 2005). Subglacial water beneath Ice Stream B, which is currently slowing down, is discharging into the Ross Sea in characteristic discharge events (Fricker et al., 2007). The temporal character of the subglacial hydrological system, which appear to control ice stream shutdown and reactivation, may thus be a crucial factor when assessing the future contribution to sea level rise from the West Antarctic Ice Sheet.

Ice velocity distribution of the Siple Coast ice streams

Figure 1: Ice velocity distribution of the Siple Coast ice streams.
Joughin and Tulaczyk, 2002.

References

  • Bougamont, M., Tulaczyk, S. and Joughin, I., 2003a. Numerical investigations of the slow-down of Whillans Ice Stream, West Antarctica: is it shutting down like Ice Stream C? Annals of Glaciology, 37: 239-246.
  • Bougamont, M., Tulaczyk, S. and Joughin, I., 2003b. Response of subglacial sediments to basal freeze-on: 2. Application in numerical modeling of the recent stoppage of Ice Stream C, West Antarctica. Journal of Geophysical Research, 108(B4, 2223): ETG20 (1-16).
  • Fricker, H.A., Scambos, T., Bindschadler, R. and Padman, L., 2007. An active subglacial water system in West Antarctica mapped from space. Science (1136897).
  • Joughin, I. and Tulaczyk, S., 2002. Positive Mass Balance of the Ross Ice Streams, West Antarctica. Science, 295: 476-480.