A study proposes a new method for recruiting trillions of microscopic sea creatures called zooplankton in the fight against climate change.
The technique harnesses the animals’ ravenous appetites to essentially accelerate the ocean’s natural cycle for removing carbon from the atmosphere, which is known as the biological pump, according to the paper in Scientific Reports
Algae blooms can grow to cover hundreds of square miles and remove about 150 billion tons of carbon dioxide from the atmosphere each year, converting it into organic carbon particulates. But once the bloom dies, marine bacteria devour the particulates, releasing most of the captured carbon back into the atmosphere.
The new technique begins with spraying clay dust on the surface of the ocean at the end of algae blooms.
The researchers found that the clay dust attaches to carbon particulates before they re-enter the atmosphere, redirecting them into the marine food chain as tiny sticky pellets the ravenous zooplankton consume and later excrete at lower depths.
“Normally, only a small fraction of the carbon captured at the surface makes it into the deep ocean for long-term storage,” says Mukul Sharma, the study’s corresponding author.
“The novelty of our method is using clay to make the biological pump more efficient—the zooplankton generate clay-laden poops that sink faster,”.
The team conducted laboratory experiments on water collected from the Gulf of Maine during a 2023 algae bloom. They found that when clay attaches to the organic carbon released when an algae bloom dies, it prompts marine bacteria to produce a kind of glue that causes the clay and organic carbon to form little balls called flocs.
The flocs become part of the daily smorgasbord of particulates that zooplankton gorge on. Once digested, the flocs embedded in the animals’ feces sinks, potentially burying the carbon at depths where it can be stored for millennia. The uneaten clay-carbon balls also sink, increasing in size as more organic carbon, as well as dead and dying phytoplankton, stick to them on the way down.
In the team’s experiments, clay dust captured as much as 50% of the carbon released by dead phytoplankton before it could become airborne. They also found that adding clay increased the concentration of sticky organic particles—which would collect more carbon as they sink—by 10 times.
At the same time, the populations of bacteria that instigate the release of carbon back into the atmosphere fell sharply in seawater treated with clay.
Sharma plans to field-test the method by spraying clay on phytoplankton blooms off the coast of Southern California using a crop-dusting airplane. He hopes that sensors placed at various depths offshore will capture how different species of zooplankton consume the clay-carbon flocs so that the research team can better gauge the optimal timing and locations to deploy this method—and exactly how much carbon it’s confining to the deep.
“It is very important to find the right oceanographic setting to do this work. You cannot go around willy-nilly dumping clay everywhere,” Sharma says. “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.”