Zooplankton poop can be used to store carbon in the deep ocean

A new study led by researchers at Dartmouth College proposes a method to enlist the help of immense populations of zooplankton in reducing atmospheric carbon.

The plan is to convert CO2 into food that these creatures will consume and send deep into the ocean through their carbon-rich waste. 

This approach aims to enhance the ocean’s natural carbon removal process – known as the biological pump – by stimulating the zooplankton’s appetite.

Using clay dust to capture carbon

The key innovation involves spreading clay dust across the ocean’s surface after massive algae blooms, which can cover hundreds of square miles. 

As these blooms die, marine bacteria normally consume the resulting particulate carbon, sending it back into the atmosphere. 

Instead, clay dust attaches to the carbon particulates, transforming them into tiny, sticky pellets. 

Zooplankton, unable to differentiate between these clay-carbon pellets and their natural food, consume them and later excrete them far below the surface , effectively storing the carbon in the deep ocean.

The role of zooplankton poop in carbon capture

“The novelty of our method is using clay to make the biological pump more efficient – the zooplankton generate clay-laden poops that sink faster,” said Mukul Sharma, the study’s corresponding author and a professor of earth sciences at Dartmouth College. 

Once digested, the clay-enriched carbon is deposited at lower depths, where it may remain for millennia. 

By accelerating the ocean’s capacity to trap carbon, this technique could offer a strategic intervention for mitigating climate change. 

The approach also takes advantage of “marine snow” – a continuous shower of organic matter, minerals, and dead organisms – which serves as a conduit for transferring nutrients and carbon to deeper waters.

Zooplankton poop and carbon storage

“This particulate material is what these little guys are designed to eat. Our experiments showed they cannot tell if it’s clay and phytoplankton or only phytoplankton , they just eat it,” Sharma said. 

“And when they poop it out, they are hundreds of meters below the surface and the carbon is, too.” 

In laboratory experiments, the team tested water collected from the Gulf of Maine during a 2023 algae bloom. 

The results confirmed that when clay dust binds to organic carbon left behind by dying algae, marine bacteria produce a sticky substance that causes the clay and organic carbon to form flocs – small, cohesive clusters.

Field testing and future research directions

The experiments revealed that the introduction of clay dust captured as much as half of the carbon released by dead phytoplankton, preventing it from re-entering the atmosphere. 

The presence of clay also increased the concentration of sticky organic particles, boosting their capacity to trap additional carbon on the journey downward. 

Adding clay reduced the numbers of bacteria that drive carbon back into the atmosphere, reinforcing the carbon’s downward path.

Exploring deployment on a larger scale

Earlier studies by co-authors Manasi Desai and David Fields from the Bigelow Laboratory for Ocean Sciences showed that clay flocs consumed and excreted by zooplankton do indeed sink more quickly. 

The team’s next goal is to test the approach by releasing clay onto phytoplankton blooms off Southern California’s coast. 

By placing sensors at various depths, researchers hope to identify the best deployment conditions and measure the carbon moved into the deep ocean, optimizing both timing and location.

“It is very important to find the right oceanographic setting to do this work. You cannot go around willy-nilly dumping clay everywhere,” Sharma noted. 

“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.”

If successful, this novel method could present a proactive solution to climate change, leveraging natural marine processes to store carbon away from the atmosphere and guiding future policy and environmental strategies.

The findings were presented at the American Geophysical Union annual conference in Washington, D.C.

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