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Underwater Glaciers Melting Much Faster Than Predicted

According to the researchers, the results also align with several recent studies of other glaciers that have indirectly suggested that theory under-predicts melting

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Antarctica, Ice
The Collins glacier on King George Island has retreated in the last 10 years and shows signs of fragility, in the Antarctic, Feb. 2, 2018. VOA

Underwater melting of tidewater glaciers is occurring much faster than was predicted, said researchers. They used a new approach to directly measure submarine melt, which could enhance projections of sea level changes.

The findings published in the journal Science could lead to improved forecasting of climate-driven sea level rise, based on a new method developed by the researchers.

“Tidewater glaciers around the globe — in Greenland, Alaska, Antarctica and beyond — are retreating and raising sea levels globally, submarine melting has been implicated as a trigger for this glacier retreat, but we have had no direct measurements of melting, let alone how it might vary in time,” said study co-author Rebecca Jackson from Rutgers University in the US.

“Our study shows that the prevailing theory significantly underestimates melt rates. These results suggest a stronger coupling between the ocean and glacier than previously expected and our work provides a path forward to improve our understanding of how the ocean impacts glaciers,” Jackson said.

For the findings, the researchers studied the underwater melting of the LeConte Glacier, a tidewater glacier in Alaska, from 2016-2018.

The suns sets against an iceberg floating in the Nuup Kangerlua Fjord near Nuuk in southwestern Greenland, Aug. 1, 2017. Greenland’s glaciers have been melting and retreating at an accelerated pace in recent years due to warmer temperatures. VOA

The research team used sonar to scan the glacier’s underwater face; downstream measurements of currents, temperature and salinity to estimate the meltwater flow; radar to measure the glacier’s speed above water; time-lapse photography to detect iceberg calving; and weather station data to measure the surface melt from the glacier.

They then looked for changes in melt patterns between August and May.

They found that melt rates are significantly higher than expected across the whole underwater face of the glacier — in some places 100 times higher than theory would predict.

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“We also found, as expected but never shown, that melt rates are higher in summer than in spring, and that variations in melt rates across the terminus cause overcutting and undercutting,” Jackson said.

While the study focused on one tidewater glacier, the new approach should be useful to researchers who study melting at other tidewater glaciers around the world, which would help to improve projections of global sea level rise.

According to the researchers, the results also align with several recent studies of other glaciers that have indirectly suggested that theory under-predicts melting. (IANS)

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Glaciers in Alaska Melting due to Climate Change

Disappearing Frontier: Alaska's Glaciers Retreating at Record Pace

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Alaska Glaciers
A sign marks where the end of the Exit glacier was in 2010 near tourists taking photos in the Kenai Fjords National Park, Alaska. VOA

Alaska will soon close a year that is shaping up as its hottest on record, with glaciers in the “Frontier State” melting at record or near-record levels, pouring waters into rising global seas, scientists said after taking fall measurements.

Lemon Creek Glacier in Juneau, where records go back to the 1940s, had its second consecutive year of record mass loss, with 3 meters erased from the surface, U.S. Geological Survey glaciologist Louis Sass told Reuters.

Melt went all the way up to the summit, said Sass, one of the experts who travel to benchmark glaciers to take measurements in the fall.

“That’s a really bad sign for a glacier,” he said, noting that high-altitude melt means there is no accumulation of snow to compact into ice and help offset lower-elevation losses.

At Wolverine Glacier on the Kenai Peninsula south of Anchorage, loss was the second highest in a record that goes back to the 1960s. Sass said it failed to match the record set in 2004 only because so much of the glacier had already melted.

Chugach National Forest Alaska
Chugach National Forest ranger Megan Parsley holds photos showing this summer’s ice loss at the face of Portage Glacier, Alaska, U.S. VOA

“The lower part’s completely gone now,” he said.

Drastic melting was also reported at Kenai Fjords National Park, which former President Barack Obama once visited to call attention to climate change. There, Bear Glacier, a popular tourist spot, retreated by nearly a kilometer in just 11 months, according to August measurements by the National Park Service.

“It’s almost like you popped it and it started to deflate,” said Nate Lewis, a Seward-based wilderness guide who takes travelers into the new lake that has formed at the foot of the shrinking glacier.

Even one of the few Alaska glaciers that had been advancing, Taku just southeast of the city of Juneau, is now losing ice at a fast clip.

Particularly ominous is the high altitude at which Taku is melting, said Mauri Pelto, who heads the North Cascades Glacier Climate Project. This year, the summer melt reached as high as 1,450 meters, 25 meters above the previous high-altitude record set just last year, he said.

Casting off chunks

Barack Obama Alaska
President Barack Obama views Bear Glacier on a boat tour of Kenai Fjords National Park in Seward, Alaska. VOA

Now that it is retreating, Taku is expected to start casting off big ice chunks, increasing Alaska’s already significant contribution to rising sea levels, according to a study co-authored by Sass and Shad O’Neel, a glaciologist with the U.S. Geological Survey. The study is scheduled to be presented at the annual conference of the American Geologic Union next week in San Francisco.

Alaska recorded its warmest month ever in July and the trend has continued.

“Alaska is on pace to break their record for warmest year unless December is dramatically cooler than forecasted,” Brian Brettschneider, a climatologist with the University of Alaska Fairbanks’ International Arctic Research Center, said in a Dec. 1 tweet.

Alaska’s glaciers account for far less than 1 percent of the world’s land ice. But their melt contributes roughly 7 percent of the water that is raising the world’s sea levels, according a 2018 study published in the journal Geophysical Research Letters and co-authored by O’Neel.

There are also local impacts. Scientists say glacial melt affects salmon-spawning streams and harms marine fish and animal habitats. It is creating new lakes in the voids where ice used to be, and outburst floods from those lakes are happening more frequently, scientists say.

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Changes in the glaciers and the ecosystems they feed has been so fast that they are hard to track, said O’Neel at USGS, who measured the melt at Wolverine Glacier in September.

“Everything’s been pretty haywire lately.” (VOA)