Some of the tiniest creatures on our planet, along with their minuscule waste, might play a crucial role in the battle against climate change. A new study reveals that applying clay dust to the surface of the ocean can transform floating carbon particles into sustenance for zooplankton. Later, these microscopic animals excrete the carbon-rich waste deep in the ocean. These carbon particles originate from carbon dioxide absorbed by marine plants, which is released back into the atmosphere when the plants die. This innovative technique redirects carbon into the marine food chain.
A study led by Dartmouth introduces a novel approach for utilizing trillions of tiny sea creatures called zooplankton in the fight against climate change by turning carbon into a food source they consume, digest, and excrete as carbon-laden waste deep in the ocean.
The method capitalizes on the voracious appetites of these creatures to enhance the ocean’s natural process of removing carbon from the atmosphere, known as the biological pump, as indicated in the paper published in Nature Scientific Reports.
The process begins by spraying clay dust on the ocean’s surface at the conclusion of algal blooms. These blooms can span enormous areas and sequester around 150 billion tons of carbon dioxide annually, converting it into organic carbon particles. However, once the blooms die, marine bacteria consume these particles, sending most of this captured carbon back into the atmosphere.
Researchers discovered that the clay dust binds to carbon particles before they can escape into the atmosphere, redirecting them into the marine food chain in the form of small, sticky pellets that are eagerly consumed by zooplankton and later excreted at greater depths.
“Typically, only a minimal amount of the carbon that gets captured at the surface makes its way to the deep ocean for long-term storage,” explains Mukul Sharma, the study’s main author and an earth sciences professor. He shared these findings on December 10 at the American Geophysical Union annual conference in Washington, D.C.
“The uniqueness of our method lies in utilizing clay to improve the efficiency of the biological pump—the zooplankton create clay-rich waste that sinks more rapidly,” adds Sharma, who received a Guggenheim Award in 2020 for this project.
“These tiny organisms are designed to consume particulate material. Our experiments demonstrated that they cannot distinguish if they’re consuming clay and phytoplankton or just phytoplankton—they simply eat it,” he states. “Then, upon excretion hundreds of meters below the surface, the carbon is also stored deeply.”
The research team conducted lab experiments on seawater samples taken from the Gulf of Maine during a 2023 algal bloom. They determined that when clay adheres to the organic carbon released as a bloom dies, it encourages marine bacteria to secrete a type of glue, causing the clay and organic carbon to form small masses known as flocs.
According to researchers, these flocs become part of the daily food supply that zooplankton feast upon. Once digested, the flocs become embedded in the animals’ feces, sinking down and potentially sequestering carbon at depths suitable for long-term storage. Moreover, the uneaten clay-carbon aggregates also sink, growing in size as they gather more organic carbon, including dead phytoplankton, on their descent, as the study observed.
In their experiments, the clay dust managed to capture up to 50% of the carbon released from deceased phytoplankton before it had a chance to escape the water. Furthermore, incorporating clay increased the concentration of adhesive organic particles – which would assimilate more carbon as they sink – by a factor of ten. Simultaneously, the researchers noticed a significant decline in the populations of bacteria that contribute to carbon release into the atmosphere in seawater treated with clay.
The flocs play a vital role in the ocean’s biological pump known as marine snow, says Sharma. Marine snow refers to the continuous shower of organic debris, minerals, and other materials that fall from the surface, nourishing the deeper waters.
“We are generating marine snow that can entomb carbon much more rapidly by explicitly attaching to a mix of clay minerals,” Sharma notes.
Zooplankton further accelerate this process with their insatiable appetites and remarkable daily journey known as diel vertical migration. Under the veil of night, these creatures—measuring roughly three-hundredths of an inch—ascend hundreds, even thousands, of feet from the deep to feast in the nutrient-rich surface waters. The scale is comparable to an entire town embarking on a nightly trek of hundreds of miles to dine at their favorite restaurant.
Once daylight arrives, these animals descend to deeper waters with the flocs in their systems, where they are released as waste. This swift process, referred to as active transport, significantly reduces the time it takes for carbon to sink to deeper levels.
Earlier this year, co-author Manasi Desai presented a project carried out with Sharma and fellow co-author David Fields, a senior research scientist and zooplankton ecologist at the Bigelow Laboratory for Ocean Sciences in Maine. Their findings confirmed that the clay flocs consumed and excreted by zooplankton indeed sink more swiftly. Desai, previously a technician in Sharma’s lab, is now part of Fields’ team.
Sharma plans to test this method in the field by spraying clay onto phytoplankton blooms off the Southern California coast using a crop-dusting aircraft. He aims to utilize sensors positioned at various offshore depths to monitor how different zooplankton species interact with the clay-carbon flocs, allowing the research team to optimize the timing and locations for deploying this method and accurately measure how much carbon is being sequestered in the depths.
“Identifying the appropriate oceanographic conditions for this work is crucial. We can’t simply scatter clay indiscriminately,” Sharma emphasizes. “We need to thoroughly understand its efficiency at diverse depths to pinpoint the best places to initiate this process before implementing it widely. We are still in the initial stages.”
In addition to Desai and Fields, Sharma collaborated with the study’s primary authors, Diksha Sharma, a postdoctoral researcher who is currently a Marie Curie Fellow at Sorbonne University in Paris, and Vignesh Menon, a recent Dartmouth graduate now pursuing a PhD at Gothenburg University in Sweden.
Additional contributors to the study include George O’Toole, microbiology and immunology professor at Dartmouth’s Geisel School of Medicine, who managed the culturing and genetic analysis of bacteria in seawater samples; Danielle Niu, who holds a doctorate in earth sciences from Dartmouth and currently serves as an assistant clinical professor at the University of Maryland; Eleanor Bates, a 2020 Dartmouth graduate now a PhD student at the University of Hawaii at Manoa; Annie Kandel, a former technician in Sharma’s lab; and Erik Zinser, an associate professor of microbiology at the University of Tennessee focusing on marine bacteria.
