Scientists told We discovered an unexpected source of food in the deep sea

In a new study, scientists from the University of Southern Denmark discovered an unexpected food source for microorganisms in the deep sea.

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The study's lead author, biologist and associate professor at the University of Sydansk Peter Steff, told  "This food source is a soluble organic material containing a diverse mix of organic compounds that may serve as food for bacteria, archaea, and fungi."

He adds: “The dissolved organic matter that leaks from the submerged particles in the deep is characterized by being rich in easily decomposed organic compounds; this is unusual at those depths, given that the dissolved organic matter that is already present in the depths of the ocean is old and largely decomposed. Therefore, the dissolved organic matter that leaks from the submerged particles forms an ‘oasis’ of decomposed organic compounds in the middle of a ‘desert’ of already decomposed organic matter, allowing microorganisms to feed on it.”

Scientists believe this discovery shows that microorganisms in the deep ocean do not live in a nutrient-poor environment as previously thought, as the immense pressure there fuels hidden microbial life, and it also reshapes the understanding of deep-sea ecosystems and how carbon is stored on Earth.

 Reef fishes swim over a reef affected by coral bleaching from high water temperature on May 08, 2024 in Trat, Thailand. Extreme heat has driven Thai sea temperatures to record highs, causing severe damage to marine ecosystems. Coral bleaching and seagrass bed degradation are threatening the ecological balance and the livelihoods of coastal communities that rely on these marine resources. 

The study concluded that this food source is caused by the enormous pressure in the deep sea, which pulls valuable nutrients from sinking organic particles known as "sea ice." These particles consist of small clumps of dead algae, microorganisms, and other organic matter that drift across the ocean. Once these particles reach depths of between 2 and 6 kilometers, the enormous hydrostatic pressure begins to push the dissolved organic matter out of them.

Regarding the effect of the enormous pressure in the deep sea, Peter explains to Al Jazeera Net: “The high hydrostatic pressure does not actually pull the submerged molecules and the cells attached to them, because the water (as well as the cells and living organisms filled with water) only compresses its volume by a very small percentage, about 3% only.”

He adds: “Instead, the membranes and cell walls of diatoms  are damaged by the high pressure. This means that these structures lose their ability to retain dissolved organic matter within the diatom cells, which leaks out of the cells under pressure. Thus, the pressure acts almost like a giant juicer, squeezing dissolved organic compounds out of the particles, and the microbes can use them immediately.”

Impact on the carbon cycle

It is estimated that submerged sea ice loses up to 50% of its original carbon and between 58% and 63% of its original nitrogen as it sinks to the ocean depths, and that most of the carbon carried by sea ice is eventually buried in deep-sea sediments.

If large quantities of carbon leak out before the molecules reach the seabed, less carbon may be permanently stored in the sediments. A large portion of the dissolved carbon remains suspended in the depths of the oceans for hundreds or even thousands of years before gradually returning to the ocean surface and then to the atmosphere. Carbon that has remained trapped for millions of years, accumulating in sediments over long periods of time, may constitute a large part of the oil and natural gas extracted today.