The seal and the robot discover a potential climate change disaster in the glacier


This is a story about nosy seals, a stray robot, and a gigantic climate change disaster waiting to happen.

Scientists tagged a southern elephant seal on Kerguelen Island, an extraordinarily remote spot in the far south of the Indian Ocean, in 2011. The seal was an 11-foot-long male weighing about 1,800 pounds, and they had equipped its head with an ocean sensor. , a device that these huge seals barely notice but has proven vital to scientific research.

Return from Antarctica in September 2011

a trip to

Antarctica in January 2011

Return from Antarctica in September 2011

Seals trek to Denman Glacier in January 2011

Return from Antarctica in September 2011

Seals trek to Denman Glacier in January 2011

Return from Antarctica in September 2011

Seals trek to Denman Glacier in January 2011

Elephant seals like these swim more than 1,500 miles south from Kerguelen to Antarctica, where they often feed on the sea floor, diving to depths that can exceed a mile below the surface. With Southern Hemisphere summer at its peak, the seal made a record-breaking trip to Antarctica, but then it went in an unusual direction.

In March 2011, it emerged offshore from a vast oceanfront glacier called Denman, where elephant seals are not generally known to go. It sank into a deep basin on the ocean floor, about half a mile below the surface. And that’s when something amazing happened: It provided early evidence that the Denman glacier could pose a major threat to global coastlines.

Seals swam in unusually warm waters, just below the freezing point, but in the Antarctic, ie warm. Because of the salt content and the extreme depths and pressures involved – in some areas the Denman Glacier rests on the seafloor more than a mile deep – such warm waters can destroy large amounts of ice. And it certainly could have done that in Denman.

However, scientists do not seem to have realized the significance of the seal data. At the time, Denman had not received much scientific attention. It didn’t help that the glacier was unusually difficult to study directly. It is located between two Antarctic research bases in Australia. Logistics is a challenge To trek from both sides, especially since the glacier is often trapped by extensive sea ice.

Researchers have already noticed that the glacier is losing some of its mass, which is a worrying sign. They also knew something else: Denman serves as a possible entry into a region of ice that is too deep and thick, even for Antarctica.

With Denman and several neighboring glaciers in place, the entrance remains closed. Opening it up would allow warmer ocean waters to begin eating away at this thicker ice, causing gradual melting and, eventually, a massive influx of new water into the ocean. That would unleash more than 15 feet of sea level rise, reshaping every coastline in the world. So the scientists flew a few planes over Denman and watched their satellites. And wait.

An amazing discovery happened in 2019. Using satellite data and other technology, scientists have published a new elevation map of all the destroyed lands under the Antarctic ice sheet. And it showed that under Denman is the deepest point of them all, about two miles deep than the Grand Canyon, or two miles below sea level. If water, rather than ice, were to fill this valley one day, the Denman glacier could raise global sea levels by nearly 5 feet.

Almost simultaneously, scientists reported something else: Denman was reeling. The “landline” area, where the glacier touches the sea floor and ocean, has retreated more than three miles toward the center of Antarctica since 1996, bringing the sea to the edge of the newly discovered valley.

In this context, the researchers have now discovered the nine-year-old measurements of the seal. “We extracted this data because we wanted to see if warm water could actually reach this glacier,” said Eric Regno, an Antarctic expert at the University of California, Irvine and one of the authors of the paper. “The answer appears to be yes.” But while the seal sensor confirmed the presence of warm water, it didn’t reveal how much of it might be colliding with the glacier.

A group of scientists based in Australia, led by Esme van Wijk of the Commonwealth Scientific and Industrial Research Organization, They were trying in 2020 To study Totten, a giant glacier hundreds of miles from Denman.

Denman and Totton are the main gateways to one of the largest chunks of thick ice in Antarctica. Both sit on top of deep channels that lead into the Aurora Subglacial Basin, a vast inland region in East Antarctica where ice lies largely below sea level, sometimes more than a mile deep. If the ocean were to be reached here it would be disastrous, making sea level rise from the complete melting of Denman look small.

Van Wijk and fellow scientist and partner Stephen Rintoul weren’t actually present at Totten — they were at home in Tasmania. But a science ship in the area deployed its research instruments, called Argo floats. These smart robots dive to great depths, periodically receiving temperature and other readings, and then reappear as long as there isn’t any ice on top. Then they send the data to humans, who are eagerly awaiting it.

But unlike that seal from a decade ago, one of the floats ended up in an unexpected place. It was blown off course by the currents, but after eight months it accidentally reappeared in front of the Denman Glacier. It turned up “in an area that we really wanted to sample, but it’s very difficult to sample with ships, and it’s often covered in very heavy sea ice,” Van Wyck said. “So for us it is a case of being very lucky.”

The robot was more thorough in its explorations than the seal. He also measured water that was warmer at very close to zero degrees Celsius. Thanks to these measurements, scientists were able to determine the amount of warm water flowing toward the Denman Glacier. It was huge.

According to Rintoul, there are “about eight rivers of the Mississippi that run into the bore.” Scientists calculated, in a paper recently published in Geophysical Research Letters, that with this volume of water and its temperature, there is potential for 71 billion tons of ice to melt from the underside of the Denman Glacier, as its “ice tongue” floats above the ocean, each year.

The warm water in question is technically called “polar deep water.” It encircles the South Pole in the mid-ocean depths, but recently, for reasons that may have something to do with changing wind patterns, a possible consequence of climate change, the circle around the continent seems to be getting tighter.

As a result, warm waters are increasingly climbing up the continental shelves and attacking glaciers at their weakest point: their bases where they rest on bedrock. “You can think of it as a blanket rolled across the sea floor,” Van Wijk said of the layer of water.

The increased interest in Denman is important because scientists have long focused on West Antarctica. These warm waters are known to melt the glaciers of Thwaites and Pine Island, causing billions of tons of ice to spill into the ocean each year.

While East Antarctica has not yet lost much, if any, ice, it potentially has more to offer than any other region of Antarctica. Like these glaciers in West Antarctica, Denman also has a serious composition. And it has a “backward” slope, which means the glacier is getting thicker, the sea floor is sloping down, and you’re moving inland from where the ice sits.

Glaciers in this situation are prone to rapid retreat called “sea ice sheet instability,” which is kind of counterintuitive. When a glacier floating on such a slope begins to melt at its base and moves back down the slope, more of its surface area is exposed to the ocean. This increases the ability of the ice to flow out and the extent to which the ice melts.

Based on measurements from the robot, Van Wijk and her colleagues can confirm that a lot of warm water is heading towards Denman. But they don’t know what happens next. There are intricate boundaries of the sea floor, including many shallow ridges, which water must pass before reaching the ice.

Given that Denman is receding, scientists are working from The working assumption is that some warm water reaches its base. Several experts said the new research represented an important step forward, but that there was still a lot to go.

Helen Amanda Fricker, an Antarctic expert at the Scripps Institution of Oceanography who was not involved in the study, said that while satellite images of massive losses of glaciers in West Antarctica have captured a lot of the scientific community’s attention, glaciers in East Antarctica are vulnerable. for the same collective loss. In the study. The basins of East Antarctica are “beginning to show signs of change,” she said, and the new paper explains that there is “enough heat flow in the ocean” to drive the melting of some very large glaciers in the region.

There’s still a lot of uncertainty about what Denman will do next, said Don Blankenship, an Antarctic expert at the University of Texas at Austin, and scientists — hamstrung by their lack of knowledge of the region — can’t predict it at this point. “The ocean transmits its heat, and now we need to ask the question, what is this heat doing inside?” He said.

Fine details of the type of bedrock the ice sits on, the exact contours of the ocean floor and the rock walls surrounding the vast glacier will be important. This will determine how quickly Denman, who is 10 miles wide, can slide and begin to slide further back into the canyon, and whether he will stumble anywhere along the way. Scientists don’t know many of those details.

“Denman is on everyone’s wish-list,” Blankenship said. Australian researchers are planning a Denman-class 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 iceberg next year.

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

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