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Home / Science / How 14 elephant seals aided an ice study in Antarctica

How 14 elephant seals aided an ice study in Antarctica



At the bottom of the planet is the Southern Ocean, its waters are cold and shaky and covered with ice many months of the year.

The edge of the ice cover, which melts during the summer and forms again in the winter, is called the marginal ice zone, and is extremely difficult to study. Large icebreakers, which have traditionally been used for research in the region, cannot continuously observe small-scale ocean activity. And sea sliders – small, relatively cheap instruments that sink into the water and bob back periodically – do not work under ice. “It’s a blind spot of knowledge in our climate system,”

; said Sebastiaan Swart, a marine biologist at the University of Gothenburg in Sweden.

What is known about the marginal ice zone is that it is an important storage system for carbon and heat emitted by humans. The global ocean as a whole stores more than 90 percent of the Earth’s excess heat, and the Southern Ocean is the portal through which much of this heat is transferred from the atmosphere. This makes the ignorance of the region particularly troubling.

But Dr Swart and Louise Biddle, a researcher also in Gothenburg, found a way around this methodological roadblock in a paper published in May. To do this, they turned to unique organic instruments that can gather stable information under the ice: southern elephant seals.

Seals in the Southern Ocean have been monitored for decades. Small sensors and trackers that are attached to their bodies and the tops of their heads, like small hats, transmit information from dives – depth, side distance, water temperature, salt – that are entered into accessible databases. open. A typical southern elephant seal is a master diver, and spends about 90 percent of its underwater time feeding on fish and squid, only surfacing for two minutes between expeditions to catch its breath before sinking. back to the stinking depths.

Because of the frequency of these dives, seal data, such as sea data, can detect small spots and streams in the water. These water flows come from many of the same forces, including winds and heat gradients, that create large currents like the Gulf Stream, but are much smaller and are called sub-muscular flows. Some are just the length of a football field and last no more than a day.

As small as they are, sub-oscillating currents have a direct effect on what Dr. Swart calls “the window between the atmosphere and the whole ocean.”

This window is known as the mixed layer, a strip of water on the surface, the depth and layering of which determines how much heat and carbon is absorbed by the ocean; the deeper and more mixed the layer, the wider the window opens and the easier it is for the ocean to absorb heat and carbon from the atmosphere. Submuscular flows change this depth and layering, and thus the window opening.

Without the technology to look under the ice cover, no one knew what kind of undercurrent flows were occurring in the marginal ice zone. The scientists thought the ice would weaken the strength of the spots, “but we don’t even have observations to show if they were even there,” said Dr. Biddle.

Then both researchers realized “that the seals had passed under the sea ice for years and years and years,” said Dr. Swart. “And because they do, they were gathering the right kind of observations for us to look at in the upper ocean under the sea ice.” Open-access stamp datasets can illustrate what kind of undercurrent flows occur under ice, and if they occur at all.

So the two turned into seals of southern elephants, who, according to them, were challenging collaborators. Many of the dives, and related data, were collected outside the study area. “You can’t tell them where to go,” Dr Biddle said, laughing. “That’s the biggest issue. They follow the food.”

But there was enough information to provide a first glimpse of the tiny currents that swirled under the ice cover of the Southern Ocean. And what Dr. Biddle and Dr. discovered. Swart, surprisingly, was that sub-tissue streams are almost as active under ice as they are in the open ocean, and that they are stronger in the mesinter when the ice is thicker.

In short, the seals showed that the water in the Southern Ocean moves much more under ice, and especially under thick ice, than many scientists had predicted. Perhaps this has to do with the variable concentration of what Dr. Biddle called the “ice discount,” which creates heat changes in the mixed layer. Maybe it has to do with certain patterns of wind and weather. Either way, it is an important finding.

“If these sub-baskets are going to change in the future, they will really change how much heat and carbon is stored in the atmosphere or in the ocean,” said Dr. Swart. “And so they are really, really important, cumulatively, to the habitable planet.

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