The petite poop from the world’s smallest animals might help suck some greenhouse gasses out of the Earth’s atmosphere. While testing a new experimental method with clay dust in a lab, a team of scientists found that the clay can help zooplankton grab onto more heat-trapping carbon dioxide. The animals could then deposit that carbon in the deepest depths of the ocean where it is stored as feces. The experimental method is not ready to be deployed into the ocean just yet, but is detailed in a study published December 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 feeding the zooplankton
The new technique begins with large blooms of microscopic plants called phytoplankton. These phytoplankton blooms remove roughly 150 billion tons of carbon dioxide from the atmosphere every year when they perform photosynthesis. They convert the greenhouse gas into organic carbon particulates that they use to eat and flourish.
However, when the phytoplankton die, marine bacteria can eat their rotting carcasses and a lot of the captured carbon dioxide is released back into the atmosphere. That’s where the zooplankton–who are animals and not plants–come in.
Sticky balls
In the new study, a team of scientists conducted lab experiments using water collected from the Gulf of Maine during a 2023 phytoplankton bloom. 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 create small, sticky balls called flocs.
According to the team, the zooplankton then gorged on the sticky flocs. Once the ball is digested, the clay embedded in the animals’ feces sinks down, potentially burying the carbon at depths where it could be stored for thousands of years. The uneaten flocs can also sink and get bigger as more organic carbon and dead or dying phytoplankton on their way down.
The clay dust captured 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 populations of bacteria that instigate the release of carbon back into the atmosphere simultaneously decreased 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 fraction of the carbon captured at the surface makes it into the deep ocean for long-term storage. The novelty of our method is using 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 trap the carbon dioxide removed by phytoplankton and, by sending these little pods through the marine food chain, confine it to the deep ocean.”
[Related: Sunken whale carcasses create entire marine cities on the ocean floor.]
According to Sharma, the carbon-clay flocs in the study would also become an essential part of the biological pump called marine snow. This constant shower 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’re creating marine snow that can bury carbon at a much greater speed by specifically attaching to a mixture of clay minerals,” said Sharma.
Every zooplankton everywhere all at once
The zooplankton can also accelerate the marine snowmaking process even more due to their daily movements. During the diel vertical migration, the zooplankton rise up to thousands of miles up from the deep to feed in the nutrient-rich water near the ocean’s top. This mega move would be like a whole town walking hundreds of miles just for dinner at their favorite restaurant every night.
“Zooplankton are eating and pooping machines,” Sharma says. “When you slice apart their poop, you see the remains of all these phytoplankton that have not been digested.”
The researchers’ method would spray clay dust on large blooms of microscopic marine plants called phytoplankton, which can cover hundreds of square miles and remove 150 billion tons of carbon dioxide from the atmosphere each year. But most of that carbon re-enters the atmosphere when the plants die. The researchers’ method diverts free-floating carbon into the marine food chain in the form of tiny sticky balls of clay and organic carbon called flocs (pictured) that 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 can cover hundreds of square miles and remove 150 billion tons of carbon dioxide from the atmosphere each year. But most of that carbon re-enters the atmosphere when the plants die. The researchers’ method diverts free-floating carbon into the marine food chain in the form of tiny sticky balls of clay and organic carbon called flocs (pictured) that are consumed by zooplankton or sink to deeper water. CREDIT: Mukul Sharma/Dartmouth.
The flocs of clay and carbon that are produced by the mix in this study would mix with all of the other matter that the zooplankton consume. When the sun rises, the carbon flocs could head back down into deeper water with the zooplankton and be deposited as feces. This dynamic–called active transport–is another critical part of the ocean’s biological pump. The sinking back down takes days off of the amount of time it takes for the carbon to reach lower depths.
“The zooplankton generate clay-laden poops that sink faster,” Sharma said. “This particulate material is what these little guys are designed to eat. Our experiments showed that they cannot tell if it’s clay and phytoplankton or only phytoplankton—they just eat it. And when they poop it out, they are hundreds of meters below the surface and all that carbon is, too.”
[Related: Sorry, zooplankton don’t want to eat your poop.]
‘We’re at the beginning’
In a future study, the team plans to conduct field experiments by spraying clay onto phytoplankton blooms off the coast of Southern California with a crop-dusting airplane. Sensors placed at various depths offshore may be able to capture how different zooplankton species eat the clay-carbon flocs. Understanding this will help the team have a better idea of the most optimal timing and locations to deploy this method and how much carbon is being put into the deep ocean.
“It is very important to find the right oceanographic setting to do this work. You cannot go around willy-nilly dumping clay everywhere,” Sharma said “We need to understand the efficiency first at different depths so we can understand the best places to initiate this process before we put it to work. We are not there yet—we are at the beginning.”
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