A little-known property of ocean “snow” may help explain why some sinking carbon travels much farther into the sea than other carbon. A ScienceDaily report on research by scientists at Scripps Institution of Oceanography at UC San Diego and the University of Lincoln says that the stickier, more viscous marine snow particles resist bacterial breakdown and can carry more carbon to the deep ocean.
Marine snow is made of small clumps of material, including mucus, animal waste, silt and the remains of microscopic plankton. As it sinks, it transports carbon from surface waters toward the seafloor. The report says researchers estimate that this process removes more than 10 gigatons of carbon from surface waters each year, while about two gigatons reach depths where carbon may remain stored for hundreds or thousands of years.
The research, published in Science on October 8, points to viscosity—the thickness and gooiness of a particle—as one factor shaping how much survives the descent. The report says the team estimates that highly viscous particles can deliver more than six times as much carbon to the deep ocean as less-viscous particles. That is an estimate based on laboratory observations and computer simulations, rather than a claim that every sticky particle carries six times more carbon.
The proposed mechanism involves where bacteria can live and how easily they can reach the particle’s material. Marine snow varies in composition and structure. The team’s imaging work found that bacteria tend to colonize less-viscous areas near a particle’s surface, while denser, stickier regions deeper inside are harder to penetrate. Bacteria can break down the accessible material, but the gooier interior can remain intact longer.
In laboratory experiments, particles with greater viscosity resisted bacterial degradation and fragmentation for longer. Computer simulations suggested that they could therefore sink farther before breaking apart. Together, those findings offer an explanation for why particles that start their journeys near the surface may transport different amounts of carbon to depth.
Seeing these interactions required a new approach. The project began in 2021, when Bryce Inman was a postdoctoral researcher at Scripps Oceanography. After several unsuccessful attempts, the team developed a working technique in 2025 that combined three-dimensional confocal microscopy with specially designed fluorescent molecules. The method let researchers reconstruct particle structure and observe bacteria moving through and interacting with it. A companion study describing the imaging approach appeared in Nature Communications.
The report identifies Inman and Farooq Azam, a Scripps microbiologist and professor emeritus, among the researchers. The Science paper’s listed authors are Inman, Stuart Humphries and Azam. Inman said, “Observing individual bacteria interacting with the physical structure of mucus had never been possible.”
The work adds a physical feature—viscosity—to the factors researchers consider when studying the ocean’s carbon pathway. The report also points to possible uses for the imaging method in studying bacteria and mucus in other settings, including coral reefs, kelp forests and plant roots. Those are potential areas for further investigation; the reported carbon findings concern marine snow.