When marine snow reaches the deep ocean, it becomes food, is chemically and biologically altered, and is gradually broken down. Deep-sea animals filter it from the water or scavenge it from the seabed; microbes and other organisms consume and repackage much of the organic matter. Only a small fraction reaches the seafloor, where it joins muddy sediment and continues decomposing.
The descent also moves particulate carbon away from the atmosphere through the biological carbon pump. Carbon carried into deep water or sediment can remain isolated for long periods, but reaching depth is not the same as permanent burial.
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What marine snow is before it reaches the abyss
Marine snow is a constantly falling mixture of particles, not a single substance. NOAA describes it as mostly biological debris produced in the upper ocean. Phytoplankton create organic matter through photosynthesis, and microbes add cells, mucus and other material. As particles collide and stick together, the aggregates can collect additional components.
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- Fecal material from zooplankton and other animals
- Microbial cells and sticky organic compounds
- Suspended mineral sediment such as silt
- Organic material carried from land
Aggregation changes how a particle sinks. A larger, denser clump can descend differently from a small, fragile flake. Currents can also carry particles sideways or move them up and down while they are sinking, so the point where material leaves surface waters is not necessarily the point where it reaches the bottom.
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How long the descent takes
There is no universal travel time. NOAA Ocean Exploration notes that the trip to depth can take weeks. A separate NOAA account from the Gulf of Alaska described aggregates reaching a 4,000-meter seafloor within about a week. That observation is a regional example, not a standard speed for every particle or ocean basin.
During the descent, the particle’s size, density, composition and freshness can all change. Organisms graze on its surface, bacteria break down compounds, and new material can attach to it. A particle arriving in deep water is therefore not chemically identical to the material that first left the sunlit ocean.
What happens in the deep water
Deep-sea animals use it as food
Sunlight does not penetrate most of the deep ocean, so sinking particles provide a major source of energy. Animals suspended in the water column can filter marine snow directly. Other animals wait on the seabed and scavenge particles after they settle. This food supply supports communities that cannot rely on local photosynthesis.
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Feeding changes the particles
Consumption does not simply remove a particle from the system. Animals fragment aggregates, digest some compounds and release waste. Other organisms can then consume that waste or incorporate it into new particles. The result is a series of transformations sometimes described as repackaging: material may become a fecal pellet, a smaller fragment or a new aggregate with different sinking behavior.
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Microbes decompose organic matter
Bacteria and other decomposers use the organic compounds in marine snow as an energy source. This process converts part of the particulate organic carbon into dissolved products and carbon dioxide. Because decomposition can occur throughout the water column, the amount and composition of material decline or change with depth. The deeper a particle travels before being consumed or dissolved, the more effectively it has exported carbon from the surface for that period.
What reaches the ocean floor
Material that survives the upper and middle ocean can settle onto the seabed. The particles mix with mineral grains and other debris to form soft, fine sediment commonly called marine ooze. Biological activity continues there: animals disturb the sediment, and microbes decompose organic compounds within it.
NOAA’s National Ocean Service reported in 2020 that about three-quarters of the deep-ocean floor is covered by ooze. In the same source, accumulation was estimated at as much as six meters of ooze per million years. Those are broad geological descriptions of seafloor sediment, not a claim that every location receives the same supply or builds up at the same rate.
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Burial in sediment can slow contact with the atmosphere, but it does not mean that every molecule is locked away permanently. Some organic matter is consumed soon after deposition; some is altered in the sediment; and only a portion can persist on geological timescales.
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How marine snow moves carbon
The sinking of particulate organic carbon is part of the biological carbon pump. Photosynthesis fixes carbon near the surface, and sinking particles transport a portion into deeper water. Once there, the carbon may remain away from the atmosphere for years, centuries or longer, depending on depth, circulation and whether it is eventually returned as dissolved carbon or retained in sediment.
A global estimate cited by NOAA’s Atlantic Oceanographic and Meteorological Laboratory, based on Osborne and colleagues’ 2023 work, found that less than 1% of particulate organic carbon generated through the biological carbon pump sinks all the way to the deep-ocean seafloor where it can be sequestered on geological timescales. The statistic concerns arrival at the seafloor and potential long-term sequestration; it does not mean that less than 1% of all exported carbon enters deep water, nor does it measure the amount temporarily stored at depth.
Depth matters because carbon that is remineralized in shallower water has a shorter route back to the atmosphere than carbon carried into the deep ocean or buried below the seabed. Marine snow therefore has a climate effect that depends on the entire pathway, not simply on how much material begins sinking.
A site-specific example: salp pellets at Station M
One observation shows why particle type and timing matter. At Station M in the northeast Pacific, Huffard and colleagues reported that salp fecal pellets delivered an estimated 45% of the total particulate organic carbon flux to the benthic boundary layer. The same study estimated that these pellets accounted for 74% of a temporary carbon surplus in May and June 2015.
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Those percentages describe one location and observation period. They are not a global share of marine-snow carbon. Salps can produce relatively large, rapidly sinking pellets, so a short-lived population increase can change the material reaching the bottom even when the broader ocean is behaving differently.
A newly reported process that can slow sinking
A March 11, 2026 news release from the Woods Hole Oceanographic Institution described research by scientists from WHOI, MIT and Rutgers on bacteria living on marine-snow particles. The study reported that these bacteria can dissolve calcium carbonate within the particles.
Calcium carbonate contributes mass to an aggregate. When it dissolves, the particle becomes lighter and may sink more slowly. Adam Subhas, a marine geochemist and study co-author, explained: “As calcium carbonate dissolves within particles, those particles become lighter and won’t sink as fast. This means that any further breakdown of organic compounds and calcium carbonate will happen at shallower depths, keeping a portion of carbon and alkalinity from reaching the deep ocean.”
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How scientists determine what is sinking
Researchers use sediment traps to collect particles as they fall through the water. Chemical measurements show how much carbon and other material is present, while genetic methods help identify the organisms that produced it.
NOAA/AOML combines sediment traps with environmental DNA (eDNA). Emily Osborne, the project’s principal investigator, said: “We’re focusing on what drives particulate carbon to be transported to the deep sea and we’re doing that, in part, by exploring what particles are biologically made up of,”
Luke Thompson, another AOML scientist, described the comparison between depths: “The sediment trap eDNA tells us which organisms are sinking to the deep ocean, month by month, and the surface water eDNA tells us what’s at the surface, and from those two pieces we can identify which organisms are being exported,”
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One free scan finds every outdated or missing driver and matches the right update for your exact hardware.Free scan · exact hardware matchThese measurements help separate seasonal changes, particle types and biological sources. NOAA/AOML notes that substantial gaps remain in understanding how the biological carbon pump operates and how it may change with climate conditions.
Comparing common marine-snow pathways
| Pathway | What happens | Carbon consequence |
|---|---|---|
| Small, fragile aggregates | They are grazed on or decomposed relatively early in the descent. | More carbon is returned to the water column before reaching great depth. |
| Large fecal pellets | They can sink rapidly, although animals and microbes may still consume them. | Carbon can be exported quickly; the amount reaching the seabed depends on the pellet’s survival. |
| Mineral-rich aggregates | Attached sediment can add density, while biological activity can later alter the particle. | Greater density may aid descent, but the eventual storage duration is not guaranteed. |
| Calcium-carbonate-bearing particles | Bacterial dissolution can reduce mass and slow sinking, according to the 2026 WHOI-reported study. | Some carbon and alkalinity may be processed at shallower depths instead of reaching the deep ocean. |
| Material deposited on the seabed | It becomes part of ooze and is further consumed or decomposed in sediment. | A fraction can remain isolated on geological timescales; arrival alone does not prove permanent burial. |
The useful comparison is therefore not simply “fast” versus “slow.” Particle freshness, composition, depth reached, sinking speed and the amount consumed or remineralized en route all determine the final outcome.
What the deep-ocean outcome means overall
Marine snow supplies energy to animals in a dark environment, redistributes nutrients and moves carbon downward. Most of the original surface material is altered before it can settle. A smaller remainder contributes to seafloor sediment, where decomposition continues and a still smaller fraction may be preserved for geological periods.
The fate of any individual particle is uncertain without measurements. A rapidly sinking pellet may carry carbon deep before being eaten; a fragile aggregate may disappear in the upper ocean; and a calcium-carbonate-bearing particle may slow as bacteria dissolve its mineral ballast. Ocean-wide estimates must therefore distinguish temporary deep storage, seafloor arrival and genuinely long-term burial.
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