A pole-to-pole global survey of viruses in the ocean has revealed 12 times more viral species than previously known. This incredible discovery was made possible by the Tara Oceans Expedition and required more than 200 scientists over the course of three years to complete. 

“Marine microbes have a profound impact on our Earth. They produce more than half of the oxygen we breathe, they move carbon dioxide from the atmosphere to the sea floor and they make up about 60 percent of the ocean’s biomass, acting as the foundation of the food web in the oceans,” said senior author Matthew Sullivan, a microbiologist at Ohio State University, in a statement. 

“Without microbes, the Earth, its oceans, and even our human bodies come to a halt. Our lab is helping researchers finally ‘see’ the hidden viruses that infect these microbes.” 

To achieve such an extensive survey of our planet’s marine viruses, a rotating team of more than 200 researchers took to the Tara sailboat and collected samples of viruses and other organisms from various ocean depths around the world. These samples – which ranged in size from the unseen such as viruses to that as big as fish eggs – were then filtered and sent to labs for analysis. 

In all, the team found 195,728 marine viral species, grouped into five main ecological zones in the ocean. This organization was unexpected given the fluidity of water and the movement of creatures through its depths.  

“When we examined the genes of the viruses in each of those communities, we found evidence of genetic adaptation to the different zones of the ocean,” said Ann C. Gregory, co-lead author of the study published in the journal Cell.

In another surprise, the team found a bounty of viral species in the Arctic in what’s been deemed a biodiversity hotspot. Such a find breaks the familiar pattern seen in larger organisms, where diversity is highest near the equator and lower near the poles.

“This suggests that the Arctic could be an unrecognized ‘cradle’ of viral biodiversity beyond the tropics and emphasizes the importance of these drastically climate-impacted Arctic regions for global biodiversity,” said co-lead author Ahmed Zayed.

“This new understanding of viruses from the northern pole to the southern pole and from the surface to 4,000 meters deep may help scientists better understand how the oceans will behave under the pressures of climate change,” he added.

The Tara is a 36-meter (118-foot) schooner dedicated to environmental research expeditions, including the recent circumnavigation of the Arctic Ocean. The study is the first to systematically sample viral populations in the Arctic.

Viruses may seem tiny and inconsequential, but they play a key role in marine ecosystems. Earth's oceans acidify due to increased levels of absorbed carbon dioxide. Yet, if this carbon dioxide can be converted to organic carbon and biomass, note the team, it can instead become particulate and sink. Viruses can help facilitate this form of sinking to help slow the rate of human-induced climate change. A new map of viral population locations, therefore, can aid scientists in further understanding this system.

The team concluded: “Together, these advances, along with the parallel global-scale ecosystem-wide measurements of Tara Oceans provide the foundation for incorporating viruses into emerging genes-to-ecosystems models that guide ocean ecosystem management decisions that are likely needed if humans and the Earth System are to survive the current epoch of the planet-altering Anthropocene.”