Sticky Gels in the Sea Are Slowing Carbon’s Descent—and That’s Bad for the Climate.

Divers may be familiar with the drifting specks of organic debris known as marine snow—tiny remains of dead algae and microorganisms that slowly fall to the ocean floor. These particles play a critical role in Earth’s climate system, as they carry and trap carbon deep under the sea, effectively removing it from the atmosphere for millennia.

Each year, this natural “carbon rain” deposits more than 50 gigatons of carbon onto the seafloor. However, new findings from a multidisciplinary team at ETH Zurich suggest this process may not be as efficient as once thought. Their research, recently published in Nature Communications, reveals that naturally occurring biogels can significantly reduce the rate at which these particles sink—allowing more carbon to return to the atmosphere rather than being stored long-term on the ocean bed.

Led by Roman Stocker, the ETH team combines expertise in microbiology, physics, oceanography, mathematics, and microfluidics. Their work uncovers how transparent, jelly-like substances produced by marine organisms—known as biogels—can entangle organic particles, drastically slowing their descent through the water column.

“The speed at which these particles fall determines how much carbon ultimately stays in the ocean,” explains Stocker. That’s because as marine snow sinks, it becomes a food source for bacteria. These microbes digest the organic matter, converting it back into carbon dioxide, which can then be released back into the atmosphere. Current estimates suggest that only about 1% of the biomass reaches the ocean floor intact.

Previous assumptions held that marine snow sank at speeds ranging from 10 to 100 meters per day. But Stocker’s research now indicates that some particles may fall at significantly slower rates due to the presence of biogels.

These gels, secreted by organisms such as algae and bacteria, serve various biological roles—from protection against predators to nutrient capture—and are found in astonishing quantities in the ocean. One study off Bermuda revealed up to two billion biogel particles in a single liter of seawater.

To study their effect, postdoctoral researcher Uria Alcolombri developed an innovative experimental setup: a 20-centimeter-high glass column filled with seawater and equipped with a counter-rotating water flow that keeps a single particle suspended in place. This allowed the team to simulate and measure the sinking rate over several days.

Using fragments of diatom shells and biogels cultured from marine bacteria, the researchers observed that particles enveloped in biogel sank almost 50% slower than those without it. “We were astonished by how strong the impact was,” Stocker noted. The gel’s low density, filamentous structure, and parachute-like behavior all contribute to greater drag, effectively acting as a brake on carbon’s descent.

These insights were also supported by mathematical modeling, helping to confirm the mechanics behind the slowed sinking. However, the researchers caution that the exact impact may vary significantly across different ocean regions due to variability in gel production and composition.

Stocker emphasizes that such microscale processes should be included in climate modeling. “There are many more of these mechanisms occurring on tiny scales. Some may enhance carbon storage, others may reduce it—but we currently know far too little,” he says. “To improve climate forecasts, we must delve deeper into the ocean’s microscopic world.

Source:https://phys.org/news/2025-05-slower-microorganisms-bad-news-climate.html

This is non-financial/medical advice and made using AI so could be wrong.