Six Times the Carbon: Gooier Ocean Snow Dives Deeper, Study Says

Not all ocean "snow" is equal, and the difference may be worth a great deal of carbon. Researchers report that the thicker and gooier a sinking particle is, the longer bacteria take to eat it and the more carbon it delivers to the deep ocean.

The study, by Bryce G. Inman, Stuart Humphries and Farooq Azam, appeared in Science on October 8, 2026, under the title "Marine snow viscosity regulates microbial degradation and the ocean carbon sink." ^[1][3] The team estimates that highly viscous particles can carry more than six times as much carbon into the deep ocean as less viscous ones. ^[1][3]

That figure is an estimate built on laboratory experiments and computer simulations. It is not a measurement of the ocean-wide effect. ^[1][3]

What marine snow is

Marine snow is the slow rain of debris that falls through the sea from sunlit surface waters. It is made of organic and inorganic material, including mucus, waste and dead plankton. ^[3]

It matters because it moves carbon. Researchers estimate that marine snow carries more than 10 gigatons of carbon out of surface waters every year, and a gigaton is a billion tonnes. Only about two gigatons make it down to depths where the carbon may stay stored for hundreds to thousands of years. ^[3] By those numbers, the great majority of the carbon that starts falling never reaches the safe depths.

Most of it is lost on the way, because bacteria feed on the particles as they sink. Each meal breaks a particle apart and returns some of its carbon to the water at shallower depths. This is the working core of what scientists call the biological carbon pump. ^[1][3]

The worm and the apple

The new work asks what makes some particles harder for bacteria to chew through. The answer the team proposes is viscosity, meaning how thick the material is and how strongly it resists flow. Honey is more viscous than water, and a particle of honey-like mucus is harder to tunnel into.

In laboratory experiments, the more viscous particles took longer for bacteria to degrade and fragment. Simulations then suggested that such particles sink farther before they break apart. ^[1][3]

Inman, who led the work, said bacteria colonize the less viscous regions near a particle's surface easily. They cannot reach the more viscous interior until they have broken those regions down. He compared it to a worm moving through an apple's flesh toward its tougher core. ^[1][3]

A particle with a thick heart therefore buys time. Time is what a sinking particle needs, since the longer it holds together, the deeper it falls before its carbon is released.

Seeing the inside of a particle

Nobody could say this with confidence until someone could see inside the mucus. The team used three-dimensional confocal microscopy, which builds a layered picture of a transparent object, together with fluorescent molecules that report how thick the material is around them. Together these let the researchers image a particle's structure and watch how bacteria interact with it. ^[1][2][3]

The technique is described in a companion paper in Nature Communications. That paper reports imaging mucus aggregates from two species of diatom, a type of single-celled algae, and mucus around the larva of an upside-down jellyfish. It presents a method for mapping viscosity and bacterial distribution. It is not a direct test of the sixfold carbon estimate. ^[2]

What the images showed surprised the researchers. Inman said mucus has a surprising amount of structure, including "bulges, crevasses." ^[1][3] To a bacterium, a particle is not a uniform blob but a landscape with soft and hard ground.

The work was done by researchers at Scripps Institution of Oceanography at the University of California, San Diego, and at the University of Lincoln. ^[1][3]

What is not yet known

The sources do not say how many particles or experimental runs lie behind the Science result. They give no uncertainty range for the sixfold figure. Nor is it established how common highly viscous particles are across ocean regions and seasons, or how well results from a laboratory dish and a simulation match marine snow falling through the open sea.

Nothing so far shows that climate models have been changed or that the global carbon budget has been recalculated. What the paper adds is a variable. Ocean carbon models have to account for how fast particles sink and how fast bacteria break them down, and viscosity is now a candidate for the link between the two.

Why it reaches beyond the sea

The stakes are the length of time carbon stays out of the atmosphere. Carbon that reaches the depths carried by marine snow can stay there for centuries or longer. A modest change in the share of particles that arrive intact could matter a lot when the flux starts at more than 10 gigatons a year.

The researchers also point to a wider use for the method. Bacteria meet mucus in coral reefs, kelp forests, plant roots and animal digestive systems. ^[1][3] The carbon result in this study concerns marine snow only, but the imaging approach gives scientists a way to look at those habitats too.

It was not quick work. Inman said the project began in 2021, and that the team had a working imaging technique only in 2025, after attempts that failed. ^[1][3]