Just a spoonful of ocean water is home to millions of microbes—tiny, single-celled organisms that play crucial roles in the ocean’s biogeochemical processes.

A new study in Science illuminates which organic particles these microbes prefer to munch on, aiding scientists’ understanding of how carbon moves through the ocean on a larger scale. 

The study reinforces the idea that “interactions of microbes and particles are relevant for the fate of carbon in the ocean,” said Josep M. Gasol, an aquatic microbial ecologist at the Institut de Ciències del Mar in Barcelona, Spain, who was not involved in the new study. 

The movement of carbon from the surface of the ocean to depth, known as the biological carbon pump, helps control the amount of carbon in the atmosphere. Microbes are key to this system, as they degrade organic particles as they consume them. That process releases carbon.

Scientists are still working to understand how different microbial communities interact to degrade particles and what affect they have on the biological carbon pump, said Mojtaba Fakhraee, a biogeochemical modeler at Yale University who was not involved in the new research.

Learning from Lipids

The study investigated how microbes break down lipids—carbon-containing molecules that make up around 20% of organic particles in the ocean. Scientists know that some lipids reach the deep ocean, whereas others are degraded along the way. The team wanted to learn what factors might influence lipids’ fate.

Researchers created small-scale laboratory experiments to simulate how bacteria interact with lipids in the ocean. They used lipids extracted from phytoplankton that contained components one might find in actual ocean particles. Bacteria used in the lab simulations were isolated from ocean particles captured by sediment traps in the Clayoquot Sound in British Columbia, Canada.

“We tried to create a system that was simple enough for us to study and observe, but not that different from what is in the ocean,” said Benjamin Van Mooy, a marine chemist at the Woods Hole Oceanographic Institution and a coauthor of the new study.

The series of experiments and measurements were “very elegant,” Gasol said. 

The research team found that even closely related bacteria preferred to consume different types of lipids and have different abilities to degrade certain lipid molecules. The contrast likely comes from differences among various bacteria’s genes that may give different degradation abilities to similar bacteria species, Gasol said.

Sinking Sea Debris

The team also found that bacteria’s lipid preferences affected how quickly a lipid was degraded, which determines how deep the particles can sink into the ocean. A particle that is quickly degraded doesn’t sink very far, whereas a particle that is slowly degraded, or not degraded at all, sinks farther. 

Some bacteria munching on the same lipids sped up degradation beyond the sum of their abilities. But others worked against each other, slowing the rate of degradation. “There’s an incredible amount of complexity,” Van Mooy said. “It takes a community of microbes with different capabilities to explain what we see in the ocean.”

The microscale findings are complementary to research that tries to understand how the biological carbon pump works over large scales and long time periods, Van Mooy said. He said he imagines that through more studies of where on Earth certain lipid molecules and bacteria occur, the new findings could eventually help scientists understand where in the ocean the biological carbon pump is most efficient.

“This small-scale microbial interaction really matters,” Fakhraee said. Having an in-depth understanding of the microscale processes in the ocean could help Earth systems modelers create more accurate projections of the effects of a warming climate, he said. “What will be the role of these microbes in controlling or mitigating the impacts of climate change?”

The findings may also eventually have applications for intentional ocean carbon sequestration, though biogeochemical engineering is in its infancy and scientists are still unsure of the long-term benefits or consequences of such experiments, Gasol said.

—Grace van Deelen (@GVD__), Staff Writer

Citation: van Deelen, G. (2024), Microbe preferences drive ocean carbon pump, Eos, 105, https://doi.org/10.1029/2024EO240457. Published on 15 October 2024.

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