Deep-sea microbes get unexpected energy boost

For many years, the deep ocean has been seen as a nutrient-poor environment where microbes living in the water survive on very limited resources, but new research challenges that idea.

A study led by University of Southern Denmark biologists with the University of Essex shows that nutrients might not be so sparse after all in the deep and that microbes have access to a previously unknown source of dissolved organic food.

The study shows that sinking organic particles, known as marine snow, begin to leak dissolved carbon and nitrogen when they reach depths of 2–6 kilometres, presenting microbes in the surrounding seawater with nutrients.

The leakage is caused by the intense hydrostatic pressure in the deep ocean.

Giant juicer

“The pressure acts almost like a giant juicer,” says first author of the study, biologist and Associate Professor Peter Stief.

“It squeezes dissolved organic compounds out of the particles, and microbes can use them immediately.”

The research team has published their findings in the journal Science Advances.

According to the study, the sinking particles may leak up to 50% of their initial carbon and 58-63% of their initial nitrogen.

'Enormous pressure'

Dr Michael Steinke, from Essex’s School of Life Sciences, said:  “Our experiments address one of the key processes that transfers energy-rich material from the sunlit ocean surface to the deep sea.

“We were surprised to realise that the enormous pressure from thousands of metres of water releases organics such as proteins and sugars from ‘marine snow’ particles.

“Whereas the current paradigm suggests that these building-blocks of life are buried in the seabed, our experiments demonstrate that they are available to fuel growth of bacteria at the base of deep-sea ecosystems.

“This international project is testament to the strength the University of Essex brings to collaborative research.”

How today’s oil and gas was created

The discovery also has implications for the global carbon cycle.

When particles lose such large fractions of their carbon before reaching the seabed, less carbon is buried in deep-sea sediments than previously thought.

Instead, the dissolved carbon remains in the deep ocean water column, where it may stay for hundreds to thousands of years before returning toward the surface ocean and the atmosphere.

In the sediment, however, carbon will be buried for millions of years, and over time, it will accumulate to huge amounts.

The oil and gas we are currently extracting was largely created in this way.

“This process affects how much carbon the ocean can store and for how long,” said Peter Stief,

“It’s relevant for understanding climate processes and for improving future models.”