This deep sea E-wall can teach us how the oceans process carbon – Mother Jones

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With its clever design features, the Benthic Rover II can roam the seabed for years to come.Madison Pobis, Copyright 2021 MBARI

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This story was originally posted by WIRED and is reproduced here as part of the Climate Office collaboration.

The benthic rover II is about the size of a compact car, although it has chunky treads, making it look more like a science tank. That, along with the two globular eye-shaped flotation devices on the front, gives it a sort of WALL-E vibe. Only instead of exploring a landscape littered with garbage, BR-II scours the Pacific seabed, 13,000 feet deep. The robot’s mission: to prowl the spongy terrain in search of clues as to how the deep ocean treats carbon.

This mission begins with a mad dash, 180 miles off the coast of Southern California. Scientists at the Monterey Bay Aquarium Research Institute lower BR-II into the water, then… drop it off. Completely detached, the robot plummets for two and a half hours, landing on the Abyssal Plains, large expanses of what you might generously call mud. “It’s both pasty and dusty,” says MBARI electrical engineer Alana Sherman, co-author of a new paper in Scientific robotics describing the discoveries of the robot’s adventures. “Which is part of why it’s a tracked vehicle, and it has these really wide treads.” This additional surface distributes the weight of the robot so that it does not sink into the sand.

If you wanted to design the perfect way to torture a robot, the deep sea would be. At these depths, the water is cold, salty (and therefore corrosive) and highly pressurized; there is a lot of liquid pushing on the robot.

As the Martian robots, this robot must be autonomous. In fact, in some ways it is even Following difficult to keep an eye on a rover at 13,000 depths than a rover on another planet. Radio waves travel well in space, it’s just that they take up to 20 minutes every way to make the trip between Earth and Mars – and good luck remotely piloting a rover in real time with that kind of delay. But the radio waves to hate the water. So, instead, BR-II uses acoustic signals to talk to another robot, a floating glider that MBARI scientists release from shore four times a year. The glider, essentially a very expensive surfboard, goes to the approximate location of the rover, reports it, collects status updates and data samples, and sends that information to a satellite for researchers to use. to access.

Since the scientists at MBARI can’t just sit in their labs and pilot the rover, it’s all on its own. But his guidelines are simple. Parked on the seabed, it lowers two oxygen sensors into the mud. This gives the robot a measure of biological activity in the sediment, as the microbes consume oxygen and spit out carbon dioxide. The rover also has a fluorescence camera system that projects a blue light, causing the chlorophyll in organic material to glow. This gives the robot an idea of ​​the amount of trash in surface water, known as “sea ​​snow“, goes down to the seabed.

The rover stays in one spot for 48 hours, then moves forward 33 feet. That’s all. “He wouldn’t know if he fell off a cliff – all he knows is I’m supposed to go 10 meters,” Sherman explains. “But luckily there are no cliffs around, so we take advantage of the simplicity of the environment to keep the robot simpler.”

You can see the two oxygen samplers under the eyeball floats. Copyright 2016

MBARI

Still, there’s a catch: oversized treads make a mess of the seabed. “Even though it’s moving very slowly, it doesn’t take much to create this huge dust storm,” says Sherman. “We always want to be in the current, so that it can push the sediment that is disturbed behind us.” So before the rover moves, it uses a sensor to get a feel for the current direction of the… uh, current, then heads straight for it.

The benthic rover does this for an entire year, unattended: park, take measurements, move 33 feet, repeat. Then the scientists steam away in their research boat to give it a battery change.

On the back of the robot are two titanium spheres, each about the size of a yoga ball and a beach ball, filled with batteries that power a year of continuous operation. When it’s time to refuel, scientists retrieve the BR-11 by sending it a signal that releases a 250-pound weight strapped to the robot’s belly. Once the weight is down, those eye-like flotation devices start to do their job. They are in fact “syntactic” foam: instead of being porous and pasty plastic filled with air, they are in fact made of a hard material and filled with small glass spheres, each containing air. . Under pressures that would collapse the typical foam on itself, the syntactic foam remains floating and propels the robot to the surface.

Scientists transport the rover aboard their boat, download data from BRI-II, replace its batteries and check for any problems. If all goes well, they release him to spend another year wandering the Abyssal Plains. The last time the scientists got out, however, they found that one of the BR-II’s engines had failed, so they had to bring it back to earth to fix it. This ended an incredible seven years of continuous operation, which they recapitulated in their current paper.

This long period of observation has given MBARI scientists unprecedented insight into what is happening in the depths, both over vast expanses of the seabed and over long time scales. This will be essential for understanding the carbon cycle of our planet. On the ocean’s surface, a galaxy of algae known as phytoplankton sequesters carbon, just as plants do on land. Then the algae are eaten by tiny animals known as zooplankton. When these creatures poop, the carbon-rich pellets descend into the water column as sea snow. Some of the waste is eaten, either along the way or by seabed creatures, but the rest is sequestered in the sediment, trapping the carbon far from the Earth’s atmosphere.

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