Sophie Nowicki on weak underbelly of West Antarctic Ice Sheet

Scientists who study polar ice are watching Antarctica’s Pine Island Glacier carefully. This glacier drains from the West Antarctic Ice Sheet – the largest mass of ice on Earth. In recent years, Pine Island Glacier has been draining the ice into the sea at a faster rate. EarthSky spoke to Sophie Nowicki of Goddard Space Flight Center in Greenbelt, Maryland about this glacier. She told us that scientists have called this area the “weak underbelly” of the West Antarctic Ice Sheet.

Dr. Nowicki said there is a small ice shelf in front of Pine Island Glacier, on the seaward side, toward the Amundsen Sea. Like a cork in a wine bottle, the ice shelf has prevented the glacier from draining straight into the ocean. But the ice shelf has weakened. It has been thinning for some time. It’s thought that relatively warm ocean water has created a widening cavity under the ice shelf that now extends to an area of 1,000 square kilometers. As the ice shelf that “corked” Pine Island Glacier has thinned, the glacier has flowed faster into the sea.

Plus, the Pine Island Glacier lacks a geological barrier to stop a retreat of the ice once it has started. In other words, there is no indication of a rise in elevation on the landward side of the glacier bed. Such a rise would help stabilize the glacier. Without this rise, the grounding line – or point where the glacier goes from land to sea – might be expected to retreat continually. Such a retreat has in fact been observed for the Pine Island Glacier. Dr. Nowicki said:

As Pine Island Glacier discharges more ice into the ocean, the sea level is going to rise. And that’s going to affect coastal regions throughout the world.

The Pine Island Glacier moves a lot of ice. Satellite measurements have shown that it has a greater net contribution of ice to the sea than any other ice drainage basin in the world. In recent years, as the glacier’s rate of ice flow into the sea has increased, the contributions of the Pine Island Glacier to sea level rise have also increased.

Ice streams account for most of the ice that melts into the ocean from the West Antarctic Ice Sheet. The Pine Island Glacier is one of the biggest of these ice streams. It is a moving river of ice that flows across the West Antarctic Ice Sheet, draining mass from the interior of the continent into the sea. The Pine Island Glacier – and another glacier, called the Thwaites – together drain 20 percent of the West Antarctic Ice Sheet.

Could the West Antarctic Ice Sheet collapse?

Large parts of the West Antarctic Ice Sheet sit on a bed that is below sea level. The ice sheet as a whole may be unstable and could disintegrate rapidly.

As a whole, the West Antarctic Ice Sheet contains a volume of water equivalent to 57 meters of global sea level rise. No one is suggesting that the entire West Antarctic Ice Sheet will melt and raise sea level by that amount. But many scientists have suggested that the West Antarctic Ice Sheet is unstable and could partially collapse. If it did, it could raise sea level by several meters.

Scientists like Sophie Nowicki believe it is critical to study the Pine Island Glacier and the West Antarctic Ice Sheet in which it flows.

These scientists believe that a warming climate could strongly influence this part of the world. At the same time, they know that they do not completely understand the processes by which the ice streams in this region drain their ice to the sea. Many questions remain, and scientists are trying to answer them.

November 9, 2011

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