Source of Antarctic ice flows may help predict changes in sea level

Scientists studying future global sea-level changes have discovered that vast flows of ice from the West Antarctic ice sheet are the product of smaller tributaries flowing from further in the continent's interior.

Scientists at the NASA Goddard Space Flight Center have been studying the history of Antarctica in the hope of predicting the contribution of the continent’s ice sheet to changes in sea level.

Since the 70s, glaciologists have been researching the source of ‘rivers’ of ice that flow hundreds of miles from the West Antarctic ice sheet into the sea, transporting the continent’s accumulated snow cover into the ocean.

The ice streams appeared to start from a near standstill but flow hundreds of feet per year faster than the surrounding ice sheet.

The point where ice streams begin to flow rapidly is marked by deep crevasses in the ice between the fast flowing ice streams and the slower moving ice sheet. But upstream, there isn’t anything on the surface to tip scientists off to where the ice streams are coming from.

Now, using data taken by the Canadian Radarsat satellite in 1997 during NASA and the Canadian Space Agency’s Antarctic Mapping Mission, researchers have discovered that the rivers of ice were actually the product of smaller tributaries flowing from further in the continent’s interior.

“We have to understand the ice streams in order to predict the future and to know what their contribution will be to sea level change,” said Dr. Robert Bindschadler, a NASA Goddard Space Flight Center glaciologist, adding that if the entire West Antarctic ice sheet were to flow into the ocean, global sea level could rise as much as 20 feet (6m).

The tributaries are well-defined regions of flowing ice that are feeding the ice streams, the research shows. But the tributaries flow more slowly than the larger ice streams and therefore aren’t marked by gaping crevasses along their borders.

The researchers have discovered that tributaries flow within valleys on the continent’s surface. Ice funnelled into the valleys becomes thicker than the surrounding ice, causing the base to become warmer and flow more easily. Then, two or more tributaries join and feed into the larger and faster-flowing ice streams, quickly moving the continent’s accumulated ice to sea.

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