A new study has proposed a novel way to combat climate change: by enlisting the help of tiny ocean creatures known as zooplankton.
The method, devised by Dartmouth College researchers, involves converting carbon from dying algae blooms into food for these microscopic animals, which then transport the carbon deep into the ocean as part of their natural digestive process.
The technique builds upon the ocean's 'biological pump' – a natural process that moves carbon from the atmosphere into the deep ocean. This pump, however, is not entirely efficient, as most carbon captured by algae blooms is released back into the atmosphere after the bloom dies and marine bacteria consume the organic particles.
The researchers, who published their findings in Nature Scientific Reports, suggest using clay dust to improve this process. Sprayed over the ocean's surface after an algae bloom, the clay binds to the carbon particulates, say the researchers, forming sticky pellets that zooplankton eagerly consume. Once digested, the carbon-laden waste is deposited at depths where it can remain trapped for thousands of years.
"Normally, only a small fraction of the carbon captured at the surface makes it into the deep ocean for long-term storage," explains Mukul Sharma, the study’s lead author and a professor of earth sciences. "The novelty of our method is using clay to make the biological pump more efficient – the zooplankton generate clay-laden poops that sink faster."
Turning algae blooms into carbon traps
Algae blooms, which can cover vast areas of the ocean, absorb around 150 billion tonnes of carbon dioxide from the atmosphere each year. However, without intervention, much of this carbon escapes back into the air when the algae die. The Dartmouth team found that adding clay changes this outcome dramatically.
In laboratory experiments conducted with water from the Gulf of Maine, researchers discovered that clay particles combine with carbon released by decaying algae to form small clumps, or 'flocs'. These flocs become part of the zooplankton diet, ensuring that the carbon is transported deeper into the ocean.
"Our experiments showed that zooplankton cannot differentiate between regular phytoplankton and clay-coated particles – they just eat them," says Sharma. "When they poop it out, they are hundreds of metres below the surface, and the carbon is, too."
Enhancing the biological pump
Zooplankton play a key role in accelerating this process through their nightly migrations from the ocean's depths to the surface to feed. Known as diel vertical migration, this behaviour allows the creatures to consume flocs near the surface and transport them to lower depths, significantly speeding up carbon sequestration.
The team also found that uneaten flocs continue to sink, growing larger as they attract more organic material, including dead algae. This effect reduces the activity of carbon-releasing bacteria, making the process even more efficient.
Testing in the real world
Sharma and his team now plan to test their method in the Pacific Ocean off Southern California. Using a crop-dusting aircraft to spray clay over algae blooms, they aim to monitor how different species of zooplankton respond and determine the most effective conditions for trapping carbon.
"It is very important to find the right oceanographic setting to do this work," says Sharma. "We need to understand the efficiency at different depths and locations before scaling up."
This innovative approach represents a promising step forward in the global effort to reduce atmospheric carbon and mitigate climate change, say the team. By harnessing the natural behaviour of zooplankton, the researchers hope to enhance the ocean’s capacity to store carbon and help protect the planet.
Find out more about the study: Organoclay flocculation as a pathway to export carbon from the sea surface
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