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Antarctic ice sheet melting from below, scientists say

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Glacial plug

The Pine Island Glacier currently acts as a plug that holds back the immense West Antarctic Ice Sheet, whose melting ice contributes to rising sea levels. If the glacier's seaward flow speeds up, there could be global consequences.

As glaciers melt, the water flows down slopes and empties into the ocean, causing sea levels to rise. Warming oceans also cause sea levels to go up, because water expands as its temperature increases. Still, understanding precisely why these changes are occurring, and how much sea levels are projected to rise in the future, is tricky, researchers have said.

Last November, a study published in the journal Science estimated that ice lost from the entire Antarctic ice sheet andGreenland ice sheet is responsible for a fifth of the 2.2 inches (5.59 cm) of sea-level rise observed since 1992.

As the Pine Island Glacier makes its seaward retreat, it also develops and drops icebergs as part of a natural cycle. In early July, a huge iceberg, measuring about 278 square miles (720 square kilometers), broke off from the Pine Island Glacier and floated freely into the Amundsen Sea.

Modeling melt

To see how much the Pine Island Glacier was melting, Holland and his colleagues installed sensors inside holes drilled 1,640 feet (500 m) through the solid ice, at various points across the glacier. The instruments measured ocean temperatures, salinity (or salt content), and the movement of warm-water currents that carve channels through the ice shelf and flow underneath it.

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