Sinking clumps of dead ocean life have been shown to leak up to half their carbon and more than half their nitrogen when exposed to the crushing pressure of the deep sea.
That pressure-driven release reveals a previously unrecognized source of food for deep-water microbes and changes how scientists account for carbon that fails to reach the ocean floor.
Deep-sea pressure test
Several miles beneath the surface, falling aggregates drift through crushing water pressure that steadily increases with depth.
Working in pressure-controlled tanks that reproduced those conditions, Peter Stief at the University of Southern Denmark (SDU) documented dissolved carbon and nitrogen streaming from the particles into surrounding seawater.
As pressure intensified to levels found two to four miles down, losses approached 50% of the particles’ carbon and as much as 63% of their nitrogen.
Such extensive leakage alters what ultimately reaches the seabed and raises the need to reconsider how deep-ocean carbon transport is understood.
Marine snow sinks
Oceanographers refer to these sinking clumps as marine snow – loose flakes made of dead organisms and sticky organic debris.
Bits shed near the surface clump together, then gravity drags them downward, carrying carbon from sunlight into darkness.
Far below, many microbes swim freely, so only dissolved food that escapes the clumps can reach them.
For decades, the deep ocean looked nutrient-poor, so leaks from falling snow could change how scientists picture deep-water diets.
Pressure causes carbon leaks
As depth increases, hydrostatic pressure builds. This pressure is from the immense weight of overlying water squeezing cells from all sides.
Rising pressure likely weakened the membranes of algae inside each clump, letting internal molecules seep into surrounding seawater.
Such draining changes the particle itself, leaving less material for deep-sea scavengers while boosting food in nearby water.
Leaked food feeds microbes
Once released, the compounds dissolved into the surrounding deep water as dissolved organic matter – carbon-rich molecules that microbes can readily absorb.
Microbes grabbed that easy fuel, and then used oxygen to break it down and release energy for growth.
Within two days, bacterial counts jumped about 30-fold in seawater fed with the leak, and oxygen use rose.
That rapid feeding suggests deep-water microbes can increase activity quickly when fresh proteins and carbohydrates reach them as dissolved food.
Less carbon reaches the seafloor
Less solid material reaching the seabed means less carbon gets trapped in sediment for geological time.
Instead, the leaked carbon stays dissolved in deep water, where slow mixing can hold it for hundreds to thousands of years.
Burial in sediments lasts millions of years, and that long squeeze-and-heat process produced much of today’s oil and gas.
“It’s relevant for understanding climate processes and for improving future models,” said Stief.
A new carbon path in the deep sea
Sinking particles help the ocean move carbon away from air, and a recent analysis argued pressure has been overlooked.
At those depths, water mixes slowly, so leaked carbon stays out of contact with the atmosphere for more than 500 years.
Zooplankton grazing and microbes living on the particles still remove plenty of carbon, so pressure-driven leakage may not dominate.
Fast-sinking blooms likely set the stage, which makes the size and timing of surface plankton booms matter for deep waters.
Species change leak levels
To build consistent particles, the team grew diatoms, tiny algae with glassy shells, then let them clump.
Across several species, pressure produced the same kind of leak, even though each species began leaking at different points.
Community makeup near the surface can therefore influence how much carbon turns into dissolved food during a rapid fall.
Other plankton groups may react differently, so scientists still need to test whether non-diatom particles leak the same way.
Further research is needed
Field sampling comes next, because lab tanks cannot capture storms, grazers, and other chaos that shapes particles at sea.
Specific chemical patterns could show up as extra dissolved sugars and proteins in deep samples compared with surface water.
Later this year, the SDU group hopes to join an Arctic trip on the German research vessel Polarstern.
Real ocean profiles will reveal whether pressure-driven leakage happens often enough to reshape deep-water food webs beyond the lab.
Models must account for pressure
Computer models usually track sinking particles as solids, so they may miss a dissolved option that feeds microbes.
Adding a pressure-dependent leak would move some carbon from particles into deep water earlier, changing where oxygen gets used.
Those adjustments could also change estimates of how much carbon reaches sediments, which influences when it returns toward the atmosphere.
Pressure appears to turn falling particles into an extra food source, letting deep microbes grow without waiting for seafloor scraps.
Confirming the leak in the open ocean will be crucial, because climate models depend on where carbon remains and how long it stays there.
The study is published in the journal Science Advances.
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