Is Pine Island Glacier the Weak Underbelly of the West Antarctic Ice Sheet?

Scott and others (2009) pointed out that the greater thinning toward the grounding line and terminus increased the surface slope and the gravitational driving stress, further promoting acceleration. Then Wingham and others (2009) reported that the 5400 km2 central trunk of the glacier had experienced a quadrupling in the average rate of volume loss quadrupled from 2.6 km3 a year in 1995 to 10.1 km3 a year in 2006. PIG had an annual volume flux at the front of 28 km3 a year, so this increase is a marked change. Their observations were that the region of lightly grounded ice at the glacier terminus is extending upstream, and the changes inland are consistent with the effects of a prolonged disturbance to the ice flow, such as the effects of ocean-driven melting. Further examination of the bed topography by Vaughan and others (2006) indicates that most of the bed of the drainage basin of PIG is more than 500 meters below sea level, and there is a particularly deep basin in the eastern section of the upper basin. The observed acceleration, retreat of the grounding line, thinning of the lower section of the glacier and the observed elevation of the basal topography provide no indication that this is not a weak underbelly of WAIS.

The evidence does indicate that one of the basic underlying principles, proposed by Mercer and Hughes, of what can stabilize or destabilize WAIS was right on the money. The evidence reviewed does not fully confirm the weak underbelly hypothesis, but it provides enough evidence that we had best monitor the situation and expand our attempts to understand it. That is just what the glaciological and scientific community are doing. A number of projects from the British Antarctic Survey, NASA and NSF will continue to expand the research in the area. In January 2008 Robert Bindschadler (NASA) landed on the floating ice shelf of PIG. They found the situation hazardous for plane landing but did leave behind several instruments. NSF has decided to fund establishment of a helicopter camp to safely study the ice-ocean interaction during the 2010-11 summer field season in Antarctica. In 2009 a team of British and American scientists deployed an autonomous robot submarine on six missions beneath the PIG ice shelf using sonar scanners to map the seabed and the ice shelf bottom. This fall NASA’s Operation Ice Bridge has focused much of its energy on the Pine Island Glacier. Seelye Martin of the University of Washington notes that “Pine Island Glacier is a major focus for our mission. We have four flights planned for this glacier. One of our hopes with these flights is to understand the detailed topography under the floating ice tongue. That topography controls the rate of melting there.”

PIGBasal

Basal topography of Pine Island Glacier region (from Vaughan et al, 2006).

References

Bindschadler, R.A., History of lower Pine Island Glacier, West Antarctica, from Landsat imagery, Journal of Glaciology, 48 (163), 536-544, 2002.

Farman, J., B. G. Gardiner and J. D. Shanklin, (1985). Large losses of ozone in Antarctica reveal seasonal ClOx/NOx interaction, Nature, 315, 207-210.

Hughes T. (1981). “The weak underbelly of the West Antarctic Ice Sheet”. Journal of Glaciology 27: 518-525.

Luchitta, B., Rosanova, C., and Mullins, K. (1995). Velocities of Pine Island Glacier, West Antarctica. Annals of Glaciology, 21, 277-283.

Molina, M.J. and F. S. Rowland (1974). Stratospheric sink for chlorofluoromethanes: Chlorine atom-catalysed destruction of ozone, Nature, 249, 810-812.

Rignot E (2008). “Changes in West Antarctic ice stream dynamics observed with ALOS PALSAR data”. Geophys. Res. Lett. 35: L12505. doi:10.1029/2008GL033365.

Rignot, E.J. (1998). Fast recession of a West Antarctic Glacier, Science, 281, 549-551.

Rignot, E.J., D.G. Vaughan, M. Schmeltz, T. Dupont, and D.R. MacAyeal (2002). Acceleration of Pine Island and Thwaites Glacier, West Antarctica, Annals of Glaciology, 34, 189-194.

Scott J.B.T., Gudmundsson G.H., Smith A.M., Bingham R.G., Pritchard H.D., Vaughan D.G. (2009). “Increased rate of acceleration on Pine Island Glacier strongly coupled to changes in gravitational driving stress”. The Cryosphere 3: 125-131. http://www.the-cryosphere.net/3/125/2009/tc-3-125-2009.html.

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