Alaskan Glaciers Melting 100 Times Faster Than Previously Thought

A NEW WAY of measuring how some glaciers melt below the surface of the water has uncovered a surprising realization: Some glaciers are melting a hundred times faster than scientists thought they were.

In a new study published today in Science, a team of oceanographers and glaciologists unpeeled a new layer of understanding of tidewater glaciers—glaciers that end in the ocean—and their dynamic processes.

“They’ve really discovered that the melt that’s happening is fairly dramatically different from some of the assumptions we’ve had,” says Twila Moon, a glaciologist at the National Snow and Ice Data Center at the University of Colorado-Boulder who was uninvolved with the study.

Some of this calving and glacial melt is a normal process that glaciers undergo during seasonal transitions from winter to summer, and even through the summer. But a warming climate accelerates glacier melting across the globe, potentially through melting across the surface of the glacier, but also through underwater melting.

“We are just super jazzed that we can even do this,” says lead author David Sutherland, an oceanographer at the University of Oregon. “We weren’t 100 percent sure it was going to work.”

Monitoring specific glaciers for a long period of time can give researchers—and high school students—an idea of climate change-induced melting. Students at Petersburg High School near LeConte Bay started collecting data about the position of the glacier’s terminus in 1983. Their noting of the glacier’s retreat several years ago alerted scientists at the University of Alaska Southeast, piquing interest in better understanding melting at the glacier.

Measuring melting masses of ice

LeConte was an ideal glacier to study because it is really accessible for a tidewater glacier, Sutherland said. A complex environment, the project required so many lines of data that teams of oceanographers and glaciologists collected data simultaneously at the glacier.

Calculating how fast a glacier melts requires more finesse than measuring a melting ice cube in a glass of water. With a glacier, you have to know how fast the ice moves into the fjord, as well as what proportion is melting and what proportion is breaking off, or calving.

It was “pretty simple in my head, and sounded good on paper,” laughs Sutherland. But navigating a boat into the fjord, where the LeConte Glacier slips into the sea, is tricky on a good day. Scientists spent weeks aboard the boat working 24 hours a day, with each scientist taking 12-hour shifts.

Mountain goats scrambled on ridges above and whales frequented the fjord, with seabirds dipping into the water. “When you aren’t wishing for better weather…it was a pretty awesome place to be,” says Sutherland.

From the 80-foot MV Stellar, oceanographers performed sonar surveys underwater, like the ones used to measure ocean depths. Instead of directing the sonar toward the ocean floor, though, they angled the sonar to collect the 3D underwater portion of the glacier face.

Oceanographers then had to know how quickly the sonar traveled through the fjord water to make accurate calculations. Further “basic” measurements of water properties, like salinity and temperature, were necessary, Sutherland explained. Dangling super-expensive instruments over the side of the boat could sometimes be tense.

Scientists repeated their observations during two summers, obtaining multiple scans each trip.“To be able to scan an entire glacier face repeatedly over the summer is not easy,” says Eric Rignot, a glaciologist at the University of California, Irvine who was not involved with the study.

Primarily a massive ice sheet, Greenland has about 200 outlet glaciers, but the water there is much colder compared to the temperature in LeConte Bay.

Alaskan glaciers primarily experience surface melt, since so few end in the ocean, said Rignot. Greenland experiences surface melt as well as melting by tidewater glaciers. But in Antarctica this submarine melting is the only type of ice melt, so understanding the processes outside Alaska are important.

If you turn the knob of climate up, like with climate change, says Sutherland, you increase the temperature of water and air and you will certainly get more melting. That can be difficult to disentangle from natural melting, though.

“These observations pretty clearly show us that there are things that we’ve been missing,” says Moon. “It’s a real call to action,” to better understand how these systems work.

Fortunately, scientists have some time to figure it out.

“These glaciers aren’t getting lost that fast…they’ll be around for decades to come,” says Sutherland.