In the pitch-black depths of the ocean, scientists have discovered something surprising: tiny particles falling from above are feeding creatures that most life on Earth will never see. A team at the University of Southern Denmark found that deep-sea pressure squeezes nutrients out of sinking particles, giving microbes living in the darkness a food source researchers never expected.
The discovery challenges a long-held assumption that the deep ocean is a desolate place with little to eat. Marine snow — made of dead algae, microbes, and other organic material drifting downward — was thought to mostly drift untouched until it finally settled on the seafloor. But the new study shows that the tremendous pressure at depths of 2 to 6 kilometers actually forces dissolved nutrients out of these particles, like water being wrung from a sponge.
"The pressure acts almost like a giant juicer," said Peter Stief, a biologist and Associate Professor at the university who led the research. "It squeezes dissolved organic compounds out of the particles, and microbes can use them immediately."
The researchers recreated marine snow in the lab using diatoms — microscopic algae that clump together as they sink. They placed these particles inside special rotating tanks that kept them floating, then measured what leaked out under pressure similar to the deep ocean. The results were striking: sinking marine snow can lose as much as 50% of its carbon and between 58% and 63% of its original nitrogen during its descent. Most of the released material was proteins and carbohydrates, which deep-sea microbes can readily consume.
The impact on microbial life was immediate. Within just two days, bacterial numbers shot up 30-fold where the leaked nutrients spread. The team also tested multiple species of diatoms and saw the same leakage pattern in each one, suggesting this process likely happens throughout oceans worldwide.
Beyond its implications for marine life, the findings could reshape understanding of Earth's carbon cycle. Scientists had assumed much of the carbon in marine snow eventually gets buried in seafloor sediments, where it can stay locked away for millions of years — the source of much of the oil and natural gas we use today. But if carbon leaks out before reaching the bottom, less may be permanently stored underground. Instead, dissolved carbon could remain suspended in deep waters for hundreds or thousands of years before slowly returning to the surface and eventually the atmosphere.
"This process affects how much carbon the ocean can store and for how long," Stief said. "It's relevant for understanding climate processes and for improving future models."
The team is now planning to take their research from the lab to the open ocean. They will search for chemical signatures of this leakage process during a future expedition to the Arctic aboard the German research vessel Polarstern. If they find evidence out in the real ocean, it would confirm that what happens in their pressure tanks is happening beneath the waves right now.