El Nino winds cause widespread ice melt in west Antarctica

Warm winds from an especially strong El Nino have caused an area of west Antarctica more than twice the size of California to partially melt, according to a new study.

The warm spell persisted for more than two weeks in January 2016, according to the study published in the journal Nature Communications.

Satellite data revealed a mix of melted snow and ice over most of the Ross Ice Shelf, a thick platform of floating ice that channels about a third of the ice flowing from the West Antarctic Ice Sheet into the ocean, the study said.

Researchers have been gathering evidence for years that warm ocean water is melting west Antarctic ice shelves from beneath, but this is one of the first times they’ve been able to document how warm air could also cause widespread melting from above.

A few weeks before the warm spell, researchers had installed the necessary instruments to investigate these processes in West Antarctica as part of a study to better understand how clouds affect the amount of energy that reaches the snow surface and influence its temperature.

“We were extraordinarily fortunate to be able to deploy state-of-the art equipment to West Antarctica just before this large melt event occurred,” said study coauthor Dan Lubin, principal investigator of the Atmospheric Radiation Measurement (ARM) West Antarctic Radiation Experiment (AWARE). Lubin is a research physicist at the Scripps Institution of Oceanography.

When Julien Nicolas, lead author of the paper, got a January 2016 alert from the AWARE expedition that the weather at their campsite atop of the West Antarctic Ice Sheet had turned unseasonably warm, he checked to see in the satellite data what was happening to the rest of west Antarctica.

The presence of water in the snow is often hard to detect from visible satellite imagery, especially if clouds block the view. Instead, Nicolas analyzed satellite measurements of the microwave radiation emitted by the snowpack, since dry and wet snows have very different microwave signatures.

What he saw during the melting event was an area of roughly 300,000 square miles, including most of the Ross Ice Shelf, that likely contained a mix of snow and water.

“What probably happened is that the surface snowpack was able to contain the meltwater, acting as a buffer and preventing the formation of melt ponds and streams that can be common on some Antarctic ice shelves,” said Nicolas, research associate at The Ohio State University’s Byrd Polar and Climate Research Center. “But we cannot rule out the presence of standing water in many locations.”

The melting was particularly interesting to scientists because it took place during one of the strongest El Nino events on record.

“This conjunction of events was no coincidence,” Nicholas said.  “It’s a pattern that is emerging. And because we expect stronger, more frequent El Ninos in the future with a warming climate, we can expect more major surface melt events in West Antarctica.”

More frequent melting would accelerate the general deterioration of the ice sheet, he said.

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By: David Beasley, Earth.com Staff Writer

Source: The Ohio State University