Gooey Ocean “Snow” Can Carry Six Times More Carbon to the Deep Sea

Tiny clumps of waste and dead plankton that drift down through the ocean carry far more carbon to the depths when they are thick and sticky, according to a new study. Researchers at the Scripps Institution of Oceanography at UC San Diego and the University of Lincoln estimate that the gooiest particles can deliver more than six times as much carbon to the deep ocean as thinner ones, ScienceDaily reported.

The finding may help explain a long-standing puzzle about why so little of the carbon removed from surface waters ends up stored deep below. The work was published Oct. 8 in the journal Science.

What is marine snow?

Marine snow is a constant fall of debris through dark ocean water. According to ScienceDaily, it includes mucus, animal feces, silt and the remains of microscopic plankton, all stuck together in small clumps.

As it sinks, it moves carbon from the upper ocean toward the seafloor. Researchers estimate it removes more than 10 gigatons of carbon from surface waters each year. Only about two gigatons reach depths where carbon can stay stored for hundreds or even thousands of years.

What did the researchers find?

They found that the viscosity of a particle, meaning how thick and gooey it is, affects how fast bacteria break it apart and how far it sinks. Bacteria feed on marine snow as it falls, so the longer a particle holds together, the more carbon it can take down with it.

In laboratory experiments, particles with higher viscosity resisted bacterial breakdown and fragmentation for longer. Computer simulations suggested those stickier particles sink to greater depths before falling apart. Based on those results, the team estimates that highly viscous marine snow can deliver more than six times as much carbon to the deep ocean as less viscous particles. The figure is an estimate drawn from experiments and simulations.

How did they see bacteria inside the particles?

The project began in 2021, when Bryce Inman, then a postdoctoral researcher at Scripps, set out to watch individual bacteria interact with the physical structure of mucus. He said that had never been possible before.

Inman and colleagues, including Scripps microbiologist and professor emeritus Farooq Azam, spent four years on the problem. Several attempts failed before the team got a working method in 2025. It combines 3D confocal microscopy, which uses light to capture images at different depths within a sample, with specially designed fluorescent molecules that make features of the material visible.

The images let the scientists study the “physical terrain” of single particles while living bacteria moved through them. A companion study in Nature Communications describes the imaging approach. It found that bacteria mostly settle near a particle’s surface, where the material is less viscous, while the denser, stickier interior is much harder to penetrate.

Inman compared it to a worm in an apple: the flesh is easy to get through, but the core is tough. Bacteria cannot reach the more viscous regions until they have broken down the material around them.

Why does it matter?

The study offers a physical explanation for why some sinking material carries carbon much farther down than other particles, even when both start near the surface. Deep-ocean storage keeps carbon away from the atmosphere for centuries or longer, so the factors that control how much gets there are part of understanding Earth’s carbon cycle, the natural movement of carbon among air, oceans, land and living things.

The researchers also say the work reaches beyond the ocean. It is the first detailed look at how living bacteria interact with the physical structure of marine snow and of mucus more broadly. Similar bacteria-mucus relationships help sustain coral reefs, kelp forests and plant root systems, as well as the digestive systems of humans and other animals.

The source material does not describe any direct change for daily life. The result adds one piece to what Inman called a “surprisingly complicated problem”: how far marine snow can sink.

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Around Prague, based on reporting by ScienceDaily