Over 5,500 new RNA viruses lurking in the murky depths of Earth have been uncovered by researchers undertaking an enormous survey of the world’s oceans. This work has been published in Science, and focused mainly on how RNA viruses influence global carbon output.   

Between 2008 and 2011, the Tara Ocean Expedition was a global research project voyaging across the world’s oceans and collecting many samples of seawater. The scientists aboard analyzed the water and found that there were hundreds of thousands of DNA viruses in these samples and that there were five major distinct ecological zones. 

Armed with this knowledge, the researchers have further analyzed these samples for RNA in the biggest-ever survey of RNA viruses in the ocean. RNA is the molecular cousin to DNA and RNA viruses are well known in human diseases – some RNA viruses include those that cause the flu and COVID-19.

Earlier this year the team published another paper in Science, where they identified over 5,500 types of RNA viruses, almost all new to science. 

In regards to the new study, "we are certainly sure that most RNA viruses in the ocean are infecting microbial eukaryotes, so fungi and protists, and to a lesser extent, invertebrates," co-first author Guillermo Dominguez-Huerta told Live Science. 

In the new paper, researchers focussed on the role that viruses played in carbon sequestration. The ocean actually produces an enormous amount of carbon (12 gigatonnes per year in fact), which equates to a third of all human-caused carbon dioxide emissions year. 

This is due to a large amount of almost microscopic creatures – plankton. When they die their carbon-filled bodies sink to the bottom of the ocean. They are then entombed for thousands, if not millions of years. This is called the biological carbon pump.

It has long been known that viruses play a key role in this carbon sequestration process and that the viruses could influence how much carbon is stored in the ocean. But the actual viruses in question were not known – until now. 

The groups think that they have identified at least 11 RNA viruses out of the 5,000 plus that are important to the carbon pump. 

Researchers also developed a computer model that could help predict the action of the carbon pump in a given area of the ocean, depending on the virus amount located in the vicinity. This model could eventually be used to inform climate models, although at the moment it is unclear how a virus can accelerate or impede the pump. 

“The findings are important for model development and predicting what is happening with carbon in the correct direction and at the correct magnitude,” said Ahmed Zayed, a co-first author of the study, in a statement.

“As humans put more carbon into the atmosphere, we’re dependent on the massive buffering capacity of the ocean to slow climate change. We’re growing more and more aware that we might need to tune the pump at the scale of the ocean,” Said Matthew Sullivan, one of the lead authors of the paper. 

“We’d be interested in viruses that could tune toward a more digestible carbon, which allows the system to grow, produce bigger and bigger cells, and sink. And if it sinks, we gain another few hundred or a thousand years from the worst effects of climate change.”

Another exciting revelation that has come out of this study is that some of the RNA viruses in the ocean have “stolen” genes from organisms that they have infected. This can help scientists identify their hosts and the functions they may have in the marine processes.