Stickier Marine Snow Carries Over Six Times More Carbon to the Deep Sea
Gooey marine snow resists bacteria and can carry more than six times as much carbon to the deep ocean, a Science study finds. How researchers saw it, and limits.
The stickiest particles of marine snow, the slow drizzle of mucus, waste and dead plankton that sinks through the ocean, can carry more than six times as much carbon into the deep sea as thinner, runnier particles. Researchers at UC San Diego’s Scripps Institution of Oceanography and the University of Lincoln reported the finding Oct. 8 in the journal Science.
The result helps answer an old puzzle. Marine snow pulls more than 10 gigatons of carbon out of surface waters each year, by the researchers’ estimate, yet only about two gigatons reach depths where it can stay locked away for hundreds or even thousands of years.
Bacteria eat the soft edges first
As the particles sink, bacteria feed on them and break them apart, releasing carbon before it gets deep. The team found that a particle’s viscosity, meaning how thick and gooey it is, controls how quickly that happens.
Bacteria settle on the less viscous material near a particle’s surface. The denser, stickier regions inside are much harder for them to get into. Lead author Bryce Inman compared it to a worm in an apple, where the flesh is easy to eat and the core is tough. In lab experiments, more viscous particles held together against bacteria for longer, and computer simulations suggested they sink deeper before falling apart. The six-fold figure is an estimate built from those experiments and models, not a direct measurement in the open ocean.
Four years to see inside a speck of slime
Inman began the project in 2021 as a postdoctoral researcher at Scripps, working with microbiologist Farooq Azam, a professor emeritus there. Several attempts failed before the team got a method working in 2025.
Their approach pairs 3D confocal microscopy, which uses light to image a sample at different depths and rebuild its shape in three dimensions, with fluorescent molecules designed to reveal the material’s structure. For the first time, the researchers could watch living bacteria move across and through individual particles. A companion paper describing the imaging method appeared in Nature Communications.
The images showed that mucus is far from a smooth blob. “There are bulges, crevasses,” Inman said, describing structure smaller than a bacterium that no one had looked at before.
Why it matters for the ocean carbon sink
Sinking particles are one of the ways the ocean keeps carbon away from the atmosphere for centuries or longer, as part of Earth’s carbon cycle. Knowing that stickiness affects how far marine snow travels gives scientists one more physical factor to account for when they estimate how much carbon reaches the deep sea. Inman called it another “very gooey” piece of a complicated problem.
The researchers say the imaging method could also be used wherever bacteria live on mucus, including coral reefs, kelp forests, plant roots and the human gut. Those uses are possibilities the team raises, not results from this study.
The study
The paper, “Marine snow viscosity regulates microbial degradation and the ocean carbon sink,” is by Bryce G. Inman, Stuart Humphries and Farooq Azam, published in Science (DOI: 10.1126/science.adx4170). Additional funding came from the Simons Foundation and the Engineering and Physical Sciences Research Council.
Source: ScienceDaily
