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The tiny poop of the world’s smallest animals could help suck some of the greenhouse gases from Earth’s atmosphere. While testing a new experimental method using clay dust in a laboratory, a team of scientists discovered that the clay can help zooplankton retain more heat-trapping carbon dioxide. The animals can then deposit that carbon in the deepest depths of the ocean, where it is stored as feces. The experimental method is not yet ready to be deployed in the ocean, but is described in detail in a study published Dec. 10 in the journal Scientific reports. The study’s findings will also be presented today at the American Geophysical Union’s annual conference.
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Phytoplankton feed the zooplankton
The new technique starts with large flowers of microscopic plants called phytoplankton. This phytoplankton bloom is removed approximately 150 billion tons of carbon dioxide from the atmosphere annually when they perform photosynthesis. They convert the greenhouse gas into organic carbon particles that they use to eat and thrive.
However, when the phytoplankton die, marine bacteria can eat their decaying carcasses and much of the captured carbon dioxide is released back into the atmosphere. That’s where zooplankton – which are animals and not plants – come into the picture.
Sticky balls
In the new studya team of scientists conducted laboratory experiments with water collected from the Gulf of Maine during a phytoplankton bloom in 2023. They sprayed clay dust on the water samples and the dust attached to the organic carbon was released by phytoplankton. This prompted marine bacteria to generate a glue-like material that causes the clay and organic carbon to form small, sticky balls called flakes.
According to the teamThe zooplankton then gorged themselves on the sticky flakes. Once the ball is digested, the clay embedded in the animals’ feces sinks, potentially burying the carbon at a depth where it can be stored for thousands of years. The uneaten flakes can also sink and grow larger as more organic carbon and dead or dying phytoplankton are on their way down.
The clay dust absorbed as much as 50 percent of the carbon released by dead phytoplankton before it could become airborne in the experiments. Adding the experimental clay increased the concentration of sticky organic particles that can collect carbon. The bacterial populations that release carbon back into the atmosphere taken at the same time in the seawater that was treated with clay.
Marine snow
Spreading clay on the surface accelerates a natural cycle known as the biological pump–where carbon is removed from the atmosphere and stored in the ocean.
“Normally, only a small portion of the carbon captured at the surface ends up in the deep ocean for long-term storage. The novelty of our method is the use of clay to make the biological pump more efficient,” study co-author and Dartmouth College planetary scientist Mukul Sharma. said in a statement. “We want to take advantage of the ocean’s biology to capture the carbon dioxide removed by phytoplankton and, by sending these tiny pods through the marine food chain, restrict it to the deep ocean.”
[Related: Sunken whale carcasses create entire marine cities on the ocean floor.]
According to Sharmathe carbon-clay flakes in the study would also become an essential part of the biological pump called marine snow. This constant rain of corpses, minerals and other organic matter falls from the ocean’s surface, transporting nutrients and food to the deeper parts of the ocean.
“We are creating marine snow that can bury carbon at a much greater rate by specifically adhering to a mixture of clay minerals,” says Sharma.
Every zooplankton everywhere at once
The zooplankton can accelerate the process of snowmaking at sea even further thanks to their daily movements. During the that vertical migrationthe zooplankton rise from the depths thousands of kilometers high feed in the nutrient-rich water near the top of the ocean. This mega-action would be like an entire city traveling hundreds of miles every night just to eat at their favorite restaurant.
“Zooplankton are eating and pooping machines,” says Sharma. “If you cut up their poop, you see the remains of all this phytoplankton that hasn’t been digested yet.”
The researchers’ method would spray clay dust on large blooms of microscopic marine plants called phytoplankton, which can cover hundreds of square kilometers and remove 150 billion tons of carbon dioxide from the atmosphere each year. But most of that carbon is returned to the atmosphere when the plants die. The researchers’ method directs free-floating carbon into the marine food chain in the form of small sticky balls of clay and organic carbon called flakes (pictured), which are consumed by zooplankton or sink to deeper water. CREDIT: Mukul Sharma/Dartmouth.
VIDEO: The researchers’ method would spray clay dust on large blooms of microscopic marine plants called phytoplankton, which could cover hundreds of square kilometers and remove 150 billion tons of carbon dioxide from the atmosphere every year. But most of that carbon is returned to the atmosphere when the plants die. The researchers’ method directs free-floating carbon into the marine food chain in the form of small sticky balls of clay and organic carbon called flakes (pictured), which are consumed by zooplankton or sink to deeper water. CREDIT: Mukul Sharma/Dartmouth.
The flakes of clay and carbon produced by the mixture in this study would mix with any other material the zooplankton consume. When the sun rises, the carbon flakes can move back to deeper water with the zooplankton and stay there deposited as feces. Called active transport, this is another crucial part of the ocean’s biological pump. Sinking back down takes days off the amount of time it takes for the carbon to reach lower depths.
“The zooplankton generate clay-laden poop that sinks faster,” Sharma said. “This particulate matter is what these little guys are designed to eat. Our experiments showed that they cannot tell whether it is clay and phytoplankton or just phytoplankton; they just eat it. And when they poop it out, they’re hundreds of feet below the surface, and so is all that carbon.”
[Related: Sorry, zooplankton don’t want to eat your poop.]
‘We are at the beginning’
In a future studythe team plans to conduct field experiments by spraying clay onto phytoplankton blooms off the coast of Southern California with a crop dust plane. Sensors placed at different depths offshore may be able to capture how different this is zooplankton species eat the clay carbon flakes. Understanding this will give the team a better idea of the most optimal timing and locations to deploy this method and the amount of carbon being dumped into the deep ocean.
“It is very important to find the right oceanographic environment to do this work. You can’t just dump clay everywhere,” Sharma said. “We need to first understand the efficiency at different depths so that we can understand where best to initiate this process before we put it into action. We are not there yet, we are at the beginning.”
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