When scientists tagged a curious seal, it led them to signs of a possible weather disaster.


The seal plunged into a deep channel in the ocean floor, approximately half a mile below the surface. And that’s when something amazing happened.

A satellite image of the Denman region of Antarctica. Mosaic of Landsat images of Antarctica

This is a story about a curious seal, a wayward robot, and a gigantic climate change disaster that may be waiting to happen.

Scientists tagged a southern elephant seal on the island of Kerguelen, an extraordinarily remote location at the southern tip of the Indian Ocean, in 2011. The seal was a male about 11 feet long who weighed nearly 1,800 pounds, and was placed an ocean sensor, a device barely noticed by these huge seals but which has proven vital to scientific research.

Elephant seals like this one swim more than 1,500 miles south from Kerguelen to Antarctica, where they often feed on the sea floor, plunging to depths that can exceed a mile below the surface. As summer in the southern hemisphere peaked, the seal made a standard Antarctic voyage, but then headed off in an unusual direction.

In March 2011, it appeared off the coast of a vast oceanfront glacier called Denman, where elephant seals are generally not known to go. She dove into a channel deep in the ocean floor, about half a mile below the surface. And that’s when something amazing happened: It provided early proof that the Denman Glacier could be a major threat to global coastlines.

The seal swam in unusually warm water, just below freezing, but in Antarctica that’s warm. Given its salt content and the depths and extreme pressures involved (in some regions, Denman Glacier rests on a sea floor more than a mile deep), water this warm can destroy vast amounts of ice. And he certainly could have done it in Denman.

However, scientists do not seem to have seen the importance of the seal data. Back then, Denman had not received much scientific attention. It didn’t help that the glacier is extraordinarily difficult to study directly. It lies between Australia’s two Antarctic research bases. Logistics are challenging for a trip from either side, especially since the glacier is often trapped by a large amount of sea ice.

The researchers had already observed that the glacier was losing some of its mass, which is a worrying sign. They also knew something else: Denman serves as a potential doorway to a region of extremely deep and thick ice, even for Antarctica.

With Denman and several other neighboring glaciers in place, the gate remains closed. Opening it up would allow warmer ocean water to start eating away at this thick ice, causing gradual melting and eventually a massive influx of new water into the ocean. That would have the potential to trigger a sea level rise of more than 15 feet, remaking all of the world’s coastlines. So, the scientists flew some planes over Denman and observed him with the satellites. And they waited.

The robot

In 2019 there was a startling discovery. Using satellite data and other techniques, the scientists have published a new elevation map of all the squashed land beneath the Antarctic ice sheet. And he showed that below Denman lay the deepest point of all, about the depth of two Grand Canyons, or two miles below sea level. If water, instead of ice, ever filled this valley, the Denman Glacier could raise global sea levels by almost 5 feet.

Almost simultaneously, the scientists reported something else: Denman was reeling. The region of its “land line,” where the glacier touches both the seafloor and the ocean, had retreated more than three miles toward central Antarctica since 1996, bringing the sea to the edge of the newly discovered canyon.

It was in this context that the researchers now unearthed the measurements of the nine-year stamp. “We excavated this data because we wanted to find out if warm water can reach this glacier,” said Eric Rignot, an Antarctic expert at the University of California at Irvine and one of the paper’s authors. “The answer seemed to be yes.” But while the seal’s sensor showed the presence of warm water, it didn’t reveal how much the glacier might be hitting.

Enter the robot.

A group of Australia-based scientists, led by Esmee Van Wijk of the Commonwealth Scientific and Industrial Research Organization, were trying in 2020 to study Totten, a gigantic glacier hundreds of miles from Denman.

Denman and Totten are two main gateways to one of the largest seams of thick ice in Antarctica. Both sit on deep channels that lead to the Aurora Subglacial Basin, a huge interior region of East Antarctica where the ice rests largely below sea level, sometimes more than a mile deep. If the ocean were to reach here, it would be catastrophic, making the sea level rise from Denman’s total melt seem small.

Van Wijk and fellow scientist and partner Stephen Rintoul were not actually present in Totten, they were at home in Tasmania. But a scientific vessel in the region deployed its research tools called Argo floats. These clever robots dive to great depths, take temperature and other readings periodically, and then surface again as long as there is no ice on them. They then radio the data to the humans who are eagerly waiting for them.

But just like the seal from a decade earlier, one of the floats ended up in an unexpected place. It was blown off course by currents but, eight months later, surfaced accidentally off Denman Glacier. It turned up “in a region that we really wanted to sample, but it’s very difficult to sample with ships, it’s often covered with quite heavy sea ice,” Van Wijk said. “So for us, it’s a case of being very lucky.”

The robot was a little more thorough in its explorations than the seal. He also measured water that was even warmer at very, very close to zero degrees Celsius. Thanks to these measurements, the scientists were able to determine the amount of this warm water that flows into the Denman Glacier. It was massive.

There are “about eight Mississippi rivers that flow into the cavity,” according to Rintoul. The scientists calculated, in a paper recently published in Geophysical Research Letters, that with this volume of water and its temperature, there is the potential to melt 71 billion tons of ice off the bottom of Denman Glacier, where its “tongue of ice” floats. ice”. over the ocean, every year.

The warm water in question is technically called “circumpolar deep water.” It circles Antarctica within the mid-ocean depths, but recently, for reasons that may have to do with changing wind patterns, a likely result of climate change, the circle around the continent appears to have narrowed.

As a result, warm water has been rising higher and higher on the continental shelves and attacking glaciers at their weak points: their bases where they rest on bedrock. “You can think of it as a blanket covering the seabed,” Van Wijk said of the layer of water.

The increased interest in Denman is significant because scientists have long focused on West Antarctica. It is well known that this warm water has been melting the Thwaites and Pine Island Glaciers, causing them to spill billions of tons of ice into the ocean every year.

While East Antarctica has not lost much ice so far, if at all, it has much more to give than any other Antarctic region. Like these West Antarctic glaciers, Denman also has a dangerous setting. It has a “retrograde” slope, meaning the glacier thickens and the seafloor slopes downward as it moves inland from where the ice settles.

Glaciers in this position are prone to rapid retreat called “sea ice sheet instability,” and it makes kind of intuitive sense. As a glacier perched on such a slope begins to melt at its base and recedes downslope, more of its surface is exposed to the ocean. That increases both the ice’s ability to flow out and the extent to which the ice can melt.

The humans

Based on the robot’s measurements, Van Wijk and his colleagues can confirm that a large amount of warm water is heading towards Denman. But they don’t know what happens after that. There are complicated seafloor contours, including several shallower ridges, that the water must traverse before reaching the ice.

Given that Denman has been retreating, scientists are operating on the assumption that some of the warm water is reaching its base. Several experts said the new research is an important step forward, but much remains to be done.

While satellite images of the massive loss of West Antarctic glaciers have captured much of the attention of the scientific community, East Antarctic glaciers are vulnerable to the same massive loss, said Helen Amanda Fricker, an expert on the Antarctica from the Scripps Institution of Oceanography which did not participate. in the study. The East Antarctic basins are “beginning to show signs of change,” she said, and the new paper shows there is “sufficient heat flow into the ocean” to cause some of the region’s largest glaciers to melt.

There’s still a lot of uncertainty about what Denman will do next, and scientists, limping because of the little they know about this region, can’t predict right now, said Don Blankenship, an Antarctic expert at the University of Texas at Austin. “The ocean is giving up its heat, and now we must ask the question, what is that heat going to do inside?” he said.

Precise details about what kind of bedrock the ice sits on, and the exact contours of the ocean floor and rock walls that encircle the wide glacier, will matter. These will determine how quickly Denman, which is 10 miles wide, can get out of his spot and start backing further into the canyon, and whether he’ll get stuck somewhere along the way. And scientists just don’t know many of those details.

“Denman is on everyone’s wish list,” Blankenship said. Australian researchers are planning a Denman expedition aboard their country’s new icebreaker, but that won’t happen until the Antarctic summer of 2024. The German research vessel Polarstern is also scheduled to reach the glacier next year.

One of the most puzzling things about climate change is that what we don’t know can do us more harm. When it comes to Denman, Van Wijk said, “we probably know more about the parts of the moon.” It is thanks in part to good fortune that we know as much as we know. We’ve heard from a seal and a robot, but it looks like it’s time to send in the humans.

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