Scientists have discovered an unexpected food source in the deep sea. This could change the way researchers understand both marine ecosystems and the Earth’s carbon cycle. A new study from the University of Southern Denmark (SDU) suggests that deep-sea microbes don’t live in such nutrient-poor environments after all.
The study found that small sedimentary particles, known as marine snow, release dissolved carbon and nitrogen as they descend into the deep ocean. The leaked nutrients provide an immediate source of nutrition for microorganisms living in the surrounding seawater.
Deep ocean pressure unlocks hidden nutrients
Marine snow consists of small clumps of dead algae, microorganisms, and other organic matter floating in the ocean. Research shows that once these particles reach a depth of about 2 to 6 kilometers, enormous hydrostatic pressure begins to push dissolved organic matter out of the particles.
“Pressure acts almost like a giant juicer,” said lead author of the study Peter Stief, a biologist and associate professor at the research center Norsee and Hadar Research Center in Denmark. “It squeezes out the dissolved organic compounds from the particles, which are immediately available to the microorganisms.”
The survey results are scientific progress “Hydrostatic pressure causes strong leakage of dissolved organic matter from ‘marine snow’ particles,” the paper says.
Researchers estimate that sinking marine snow can lose up to 50% of its original carbon and 58% to 63% of its original nitrogen during its descent through the deep ocean.
This discovery could reshape our understanding of the carbon cycle
This result also has important implications for the Earth’s carbon cycle.
Scientists have long thought that much of the carbon transported by marine snow would eventually become buried in deep-sea sediments. However, if large amounts of carbon escape before the particles reach the ocean floor, the amount of carbon permanently stored in sediments may be lower than previously thought.
Instead, much of that dissolved carbon remains suspended in deep ocean waters, where it remains for hundreds or even thousands of years, before gradually returning to the surface ocean and eventually the atmosphere. In contrast, carbon buried in seafloor sediments can remain trapped for millions of years and accumulate over vast amounts of time. Much of the oil and natural gas extracted today was formed through this long-term burial process.
“This process affects how much carbon the ocean can store and for how long. This is relevant for understanding climate processes and improving future models,” says Peter Stief.
Simulation of marine snow under extreme pressure
To investigate this process, researchers recreated marine snow in the lab using diatoms, microscopic algae that solidify naturally when they sink into the ocean.
The research team placed these artificial particles inside a specially designed rotating pressure tank to keep the marine snow suspended instead of settling. This setup allowed the researchers to measure how much carbon and nitrogen escape under conditions similar to those found in the deep ocean.
Their experiments found that up to half of the particles’ carbon content leaked out during settling. Most of the released material consisted of proteins and carbohydrates that can be easily consumed by free-living deep-sea microorganisms.
Microorganisms react almost immediately
Leaked nutrients rapidly promoted microbial growth.
Within just two days, bacterial abundance increased 30-fold and respiration rates increased dramatically. These results demonstrate that dissolved organic matter released from marine snow provides a rapid and valuable energy source for microorganisms living in the deep sea.
The researchers also observed the same leakage pattern in multiple species of diatoms, suggesting this mechanism is likely widespread in oceans around the world.
Next destination: Arctic Ocean
The next stage of research will move from the laboratory to the open ocean.
The research team plans to search for the molecular fingerprints of this process in both surface waters and the deep sea during future Arctic expeditions by German research vessels. Polaris. Detecting these signatures in nature would help confirm that the pressure-induced leaks observed in the laboratory occur throughout the deep ocean.
The study, “Hydrostatic pressure causes strong leakage of dissolved organic matter from ‘marine snow’ particles,” was authored by Peter Stief, Jutta Niggemann, Margot Bligh, Hagen Buck-Wiese, Urban Wünsch, Michael Steinke, Jan-Hendrik Hehemann, and Ronnie N. Glud.
This research was supported by the Danish National Research Foundation, the European Union’s Horizon 2020 research and innovation program, and the Danish Independent Research Fund.
