Gooier Marine Snow Locks Away More Ocean Carbon

In the deep ocean it never stops snowing. Clumps of mucus, dead plankton, fecal pellets and silt drift down from the sunlit surface, and they carry carbon with them. Scientists estimate this marine snow moves more than 10 gigatons of carbon away from the surface every year. Only about two gigatons are believed to sink deep enough to stay locked away for hundreds to thousands of years. A study published October 8, 2026 in Science points to one reason for that gap, and it is not a chemical one. It is how gooey the snow is.

A problem of plumbing, not chemistry

The ocean's biological carbon pump is simple in outline. Plankton at the surface take up carbon dioxide, die or get eaten, and their remains aggregate into particles that sink. Bacteria colonize those particles on the way down and break them apart, releasing much of the carbon back into the water before it reaches depth. Whether a given particle delivers its carbon to the deep sea or gives it up near the surface depends on a race between how fast it sinks and how fast it is degraded.

That race has been hard to study at the scale where it happens: individual bacteria working their way into individual particles. The new paper, led by Bryce Inman at UC San Diego's Scripps Institution of Oceanography with colleagues at the University of Lincoln in the U.K., goes down to that scale.

Mapping the inside of a snowflake

The team used molecular rotors, fluorescent molecules whose glow changes with the viscosity around them, combined with 3D confocal microscopy. That let them map the nanoscale viscosity of natural aggregates and watch live bacteria move through them. According to Scripps, it is the first time scientists have observed live bacteria interacting with the physical structure of marine snow, or of any mucus. The method itself is described in a companion paper in Nature Communications. Developing it took years: Inman began in 2021, and the approach only worked in 2025.

What they saw was structure. Aggregates are not uniform blobs. They are microhabitats with less viscous regions, often near the surface, that bacteria can colonize easily, and more viscous regions that act as a barrier to bacterial infiltration until the outer layers are broken down. Inman compares it to a worm in an apple: the flesh is easy to get into, the core is tough to chew through.

The carbon that reaches the deep ocean may depend less on what a particle is made of than on how hard it is to get into.

From the microscope to the carbon budget

In laboratory experiments, the researchers measured how fast bacteria lower the viscosity of aggregates as they degrade them. More viscous aggregates took longer to degrade and fragment. The team then fed those rates into computer simulations of sinking particles. In the simulations, more viscous particles sank farther before being consumed, and the most viscous could deliver more than six times as much carbon to the deep ocean as low viscosity ones.

That last number is the one that will travel, and it needs its label attached. The sixfold figure comes from modeling built on laboratory measurements. It was not measured by tracking real particles to the bottom of the ocean. The direction of the effect is supported by the experiments. Its size in the real ocean is an estimate.

Why it matters for climate models

Climate projections need to know how much carbon the ocean will keep absorbing and storing. The biological pump is one of the hardest parts to model, because it depends on processes at the scale of single particles that no global model can resolve directly. A physical property like viscosity, if it turns out to vary systematically with the kind of plankton producing the mucus, could become a parameter models can use. The study does not provide that yet. It provides the first tool that could.

It also cuts against an intuitive picture of the ocean as a chemistry problem. The carbon is the same carbon whether it sinks or not. What changes its fate is something closer to material science: the texture of slime. The authors point out that the same kind of mucus and microbe interaction matters in coral reefs, kelp forests, plant roots and human guts, which makes the imaging method potentially useful far beyond oceanography.

The ocean already stores carbon on a scale no engineered system comes close to, and debates about how much it can absorb usually focus on temperature and chemistry. A study like this is a reminder that some of the controls sit in places nobody could see until recently. The next step is to find out whether the slime is changing too.