The ocean’s depths are known for their crushing pressure, a force that now appears to play a surprisingly significant role in the marine carbon cycle. New research reveals that as organic matter sinks from the sunlit surface waters to the seafloor, immense pressure causes it to break down, releasing dissolved carbon and nitrogen—a previously underestimated process that impacts how nutrients are distributed and how carbon is stored in the deep ocean.
This leakage, documented in laboratory experiments simulating deep-sea conditions, suggests that less carbon reaches the ocean floor as solid particles than previously thought. Instead, it’s being made available to microbes in the water column, altering the food web and potentially influencing the ocean’s ability to sequester carbon dioxide from the atmosphere. Understanding this pressure-driven release is crucial for refining climate models and predicting future carbon storage capacity.
Researchers at the University of Southern Denmark (SDU) led the study, published in the journal Science Advances. They meticulously recreated the extreme pressures found two to four miles beneath the ocean surface in controlled tank environments. Using these tanks, they observed that sinking particles, commonly referred to as “marine snow,” lost up to 50% of their carbon and 63% of their nitrogen as pressure intensified. This finding challenges conventional understanding of carbon transport in the ocean.
Marine snow, as described by the National Oceanic and Atmospheric Administration (NOAA), consists of loose flakes of dead organisms and organic debris. These particles form near the surface as bits of organic matter clump together, then slowly descend into the darkness, carrying carbon from the sunlit zone to the deep. For decades, scientists believed these particles were the primary food source for deep-sea organisms, but the new research suggests a more complex picture.
How Pressure Weakens Particles
The study found that increasing hydrostatic pressure—the weight of the water above—weakens the membranes of algae within the sinking particles. This weakening allows internal molecules to seep into the surrounding seawater. The released carbon and nitrogen then dissolve, becoming available to microbes. This process effectively transforms solid carbon into dissolved organic matter, a readily absorbable food source for deep-sea microorganisms.
Within two days of the simulated leakage, bacterial counts in the experimental tanks increased by approximately 30-fold, and oxygen consumption rose significantly, indicating rapid microbial growth. This suggests that deep-water microbes can quickly capitalize on the fresh influx of dissolved proteins and carbohydrates.
Implications for Carbon Sequestration
The leakage of carbon from sinking particles has significant implications for long-term carbon storage. Less solid material reaching the seafloor means less carbon is trapped in sediments for geological timescales—potentially millions of years. Instead, the dissolved carbon remains in the deep water, where it can be held for hundreds to thousands of years due to slow mixing rates. The long-term burial of carbon in sediments is a key process in the formation of fossil fuels.
Peter Stief of SDU emphasized the relevance of these findings for climate modeling, stating, “It’s relevant for understanding climate processes and for improving future models.” A recent analysis highlighted that pressure’s role in carbon cycling has been historically overlooked.
Species-Specific Leakage
The research team also investigated how different species of diatoms—tiny algae with glassy shells—responded to pressure. They found that while the type of leakage was consistent across species, the point at which leakage began varied. This suggests that the composition of plankton communities near the surface can influence the amount of carbon that turns into dissolved food during its descent. Further research is needed to determine whether other plankton groups exhibit similar leakage patterns.
Next Steps: Field Research in the Arctic
The next phase of research will involve field sampling to validate the laboratory findings in a natural ocean environment. Lab tanks, while controlled, cannot fully replicate the complex conditions of the open ocean, including storms, grazing by marine organisms, and other factors that influence particle behavior. Later this year, the SDU group plans to join an Arctic research expedition aboard the German research vessel Polarstern. This expedition will allow them to collect real-world data and assess the prevalence of pressure-driven leakage in deep-water food webs.
incorporating a pressure-dependent leakage mechanism into computer models could improve the accuracy of climate predictions. Current models typically track sinking particles as solids, potentially overlooking this important dissolved component. Accurately accounting for where carbon resides and for how long is critical for understanding the ocean’s role in regulating Earth’s climate.
The study underscores the interconnectedness of ocean processes and the need for continued research to refine our understanding of the marine carbon cycle. Confirming the extent of this leakage in the open ocean will be crucial, as climate models rely on accurate representations of carbon storage and transfer.
Researchers will continue to analyze data from the Arctic expedition and refine their models to better reflect the complex interplay between pressure, carbon transport, and microbial activity in the deep sea. The team anticipates publishing further findings in the coming year.
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