Khumbu Glacier in Nepal offers clues to rapid retreat of ice

Khumbu Glacier in Nepal offers clues to rapid retreat of ice

By Anne Snabes, Dec. 19, 2019 –

The Khumbu Glacier in the Himalayas retreated rapidly in the past, offering clues to how the glacier will behave in the future, University of Maine research suggests.

Laura Mattas, a master’s student at the university, conducted field research this summer on the Khumbu Glacier in Nepal. She presented her research this fall at the Comer Climate Conference, an annual meeting in Wisconsin of climate scientists from across the country.

According to the National Snow & Ice Data Center, glaciers globally are retreating at “unprecedented rates.” A glacier can retreat by shortening in length or by thinning. In the Khumbu Valley, Mattas and her colleagues found moraines, which are rock and other sediment that were inside, on top of or below a glacier and that were altered by the glacier. The location of the moraines indicated that the glacier retreated quickly at some point since the last ice age. Mattas said that the glacier is able to undergo a “large and rapid change,” which means that it may also change rapidly in the future.

“If that’s the case, that’s a lot of meltwater that’s flowing down valley,,” she said. “Who knows if there’s the infrastructure to deal with” the surge.

Laura Mattas, a master’s student at the University of Maine, is following the retreat of the Khumbu Glacier. (Anne Snabes/MEDILL)

Mattas and other researchers collected 77 samples of rock from the valley, which can demonstrate how the glacier has behaved from the last ice age to today.

“That could predict what the future warming of this area looks like,” she said, “because if it’s known to go fast and just give all that meltwater, then it could be predicting that this glacier is … going through an irreversible retreat.”

Mattas said she and the research group found moraines at a village called Dingboche and at a nearby settlement called Lobuche. A scientist previously found that the moraines in Dingboche were formed during the last ice age. The moraines at Lobuche, on the other hand, are more modern, but Mattas still has to determine their exact date.

The scientists did not see any moraines between Dingboche and Lobuche.

“As we walked from Dingboche to Lobuche, there was absolutely nothing,” Mattas said.

The lack of moraines between the two locations suggests that the glacier melted quickly. If the glacier had retreated more gradually, it would have formed moraines about every few thousand years, so the terrain would show several lines of moraines in the space between Dingboche and Lobuche.

Mattas said a glacier has to sit in one place long enough to form moraines. But in this case, the glacier moved too quickly.

Mattas’ conclusion that the Khumbu Glacier retreated quickly is a preliminary field observation, but it still needs to be supported by data. The samples of rock that Mattas and her colleagues collected may provide the evidence needed to back her claim. They retrieved the rock by drilling holes in boulders. The scientists will employ a technique called Beryllium-10 dating, which can tell them the age of the moraines. This age gives researchers an approximation of when the glacier retreated, according to Mattas.

The research team sits by moraines that were formed by the Khumbu Glacier. The research trip was part of National Geographic and Rolex’s Perpetual Planet Extreme Exhibition: Everest. Photo courtesy of Laura Mattas.

Sidney Hemming, a professor of earth and environmental sciences at Columbia University, said she agrees that in order to accommodate the researchers’ observations, there had to be a “really quick retreat.” Hemming said that it does not really matter what the ages of the two moraine belts are.

“The fact that there’s this big space in between them with no moraines in there means that there had to be a rapid retreat, right?” she explained.

Mattas said she and other researchers are currently studying the past so they can learn what the Khumbu Glacier is capable of doing in the future.

“We’re trying to see how it reacted in the past,” she said, “and from that data, we hope to then use a predictive model to see if that is possible in what we’re seeing today.”

Photo at top: The Khumbu Glacier retreated rapidly at some point between the last ice age and today, and Laura Mattas is trying to determine the exact date of the retreat. She and her colleagues conducted research in the Khumbu Valley as a part of National Geographic and Rolex’s Perpetual Planet Extreme Exhibition: Everest. Photo courtesy of Laura Mattas.

Tiny shells reveal clues to ocean health in North Pacific

Tiny shells reveal clues to ocean health in North Pacific

By Anne Snabes, Dec. 19, 2019 –

Calcium carbonate, a primary ingredient in the shells of tiny marine organisms, reduces the acidification of our world’s oceans.

The ocean is approximately 30% more acidic than when the Industrial Revolution began, and carbon dioxide emissions from human use of fossil fuels have greatly contributed to this increase.

When microscopic organisms called zooplankton and phytoplankton die, they sink to the bottom of the ocean, and their calcium carbonate shells dissolve. This process makes the ocean less acidic. But new research suggests that scientists don’t fully understand how calcium carbonate dissolves in the ocean.

This ostracod, which is a kind of zooplankton, has a calcium carbonate shell. (Wikimedia Commons/ Anna Syme)

Kassandra Costa, a postdoctoral scholar at Woods Hole Oceanographic Institution in Massachusetts  found that calcium carbonate dissolves at a shallower sea floor depth in the North Pacific Ocean than scientists predicted. She presented her research this October at the Comer Climate Conference, an annual meeting of climate scientists in Southwest Wisconsin. Costa told the Medill News Service that there could be a problem with how scientists predict the depth at which calcium carbonate dissolves.

Kassandra Costa talks about clues to climate change revealed in tiny shells at the Comer Climate Conference in October. (Abigail Foerstner/MEDILL)

Costa said that when carbon dioxide enters the ocean, it reacts with water and carbonate ions to produce bicarbonate. When calcium carbonate dissolves in water, carbonate ions are produced. This process replenishes the carbonate ions that were used up by carbon dioxide when it entered the ocean.

Costa said carbonate ions pick up some of the protons (positive particles in atoms) in the water, which makes the water less acidic. Because calcium carbonate is a source of the carbonate ion, it reduces ocean acidification.

Calcium carbonate dissolution makes the ocean less acidic. (Photo: Flickr/Joe Lin. Text in graphic/Anne Snabes)

“When calcium carbonate dissolves in the ocean, as she mentioned, that essentially buffers the acidity that is added by CO2,” said Jerry McManus, a geochemistry professor at Columbia University.

Costa said scientists predicted that calcium carbonate can be found at the bottom of the North Pacific up to depths of 4,400 meters (14,432 feet). This prediction was made using chemistry measurements and theory. Through research, Costa and her colleagues discovered that calcium carbonate can in fact only be found up to depths of about 3,000 meters (9,840 feet) some two-thirds of the predicted value.

Costa sailed in 2014 with other researchers 500 km ( about 311 miles) off the coast of Oregon to the Juan de Fuca Ridge, where she collected sediment from the ocean floor by using a device called a multi-core. She said the researchers gently lower the device to the bottom of the ocean. It punches a hole in the sediment to extract a core of it. Then the researchers bring the instrument and the core back to the boat. The sediment in the multi-core contains clay as well as calcium carbonate from dead zooplankton and phytoplankton.

These tiny organisms are at the bottom of the ocean food chain, feeding other marine species.

Calcium carbonate dissolves in a gradient in the North Pacific. At a depth of 2,300 m (7,544 feet) the sediment at the ocean floor is 60% calcium carbonate and 40% clays. At a 3,000 m sea floor depth, the sediment is only 10% calcium carbonate, as most of the material has dissolved. This means that there is little calcium carbonate in the North Pacific at depths below 3,000 m.

McManus, who also went on the research trip, said Costa’s observation points to the limitation of “broad-brush theoretical constructions.” Costa made actual measurements, instead of solely relying on theory.

Costa said the mismatch between the expected and observed depths suggests that something is missing in our understanding of calcium carbonate dissolution in the sea.

“There’s something extra about the calcium carbonate in the North Pacific that makes it, in actuality, dissolve at much shallower depths than we expected,” she said.

Costa told her audience at the Comer Conference that scientists have already observed calcium carbonate dissolving on the sea floor due to human activity that produces CO2.

Because calcium carbonate is dissolving at shallower depths than predicted, there may be a slightly lower amount of calcium carbonate in the North Pacific than expected. This would mean that calcium carbonate could not compensate for as much carbon dioxide as scientists expected, but more research needs to be done.

Costa said it will take thousands of years for calcium carbonate in the ocean to run out.

“Once that buffer does run out, the acidification of the ocean will proceed much more rapidly,” she explained.

Photo at top: Dan Armhein, Costa and Deborah Leopo work with a sediment core that was collected during a 2017 trip to the North Atlantic. (Courtesy of Kassandra Costa)


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