New research provides the most complete account to date of the viruses that impact the world's oceans, increasing the number of known virus populations tenfold.

"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," said Ahmed Zayed, co-lead author of the study and microbiology doctoral student at The Ohio State University.

Researchers analyzed marine samples far and deep in an effort to understand the complexities of viruses, which are increasingly being recognized as important players in the oceans' role in tempering the effects of climate change.

This new study brings the total known marine viral populations within the ocean close to 200,000 - work that will help scientists better understand their influence throughout the world, including their part in delivering carbon deep into the sea, protecting the atmosphere from further damage. The study, led by researchers at Ohio State, appears online today (April 25) in the journal Cell.

"This is a massively expanded 'catalog' of ocean viruses, which we used to draw the first global map of viral diversity," Zayed said.

Added Ann Gregory, co-lead author of the study, "What was really exciting was now being able to study these viruses at two important levels - the population level and by looking at genetic variation within each population, which tells us about evolution.

"We have expanded the number of known viral populations more than tenfold and this new map will help us understand the impact of ocean viruses on a global level," said Gregory, formerly of Ohio State and now a postdoctoral trainee in Belgium at KU Leuven.

The samples were collected during the unprecedented three-year Tara Oceans Expedition, in which a team of more than 200 experts took to the sea to catalog and better understand the unseen inhabitants of the ocean, from tiny animals to viruses and bacteria.

In addition to the prior research in the temperate and tropical oceans, this new work includes samples from the schooner's circumnavigation of the Arctic Ocean - the area most significantly impacted by climate change.

The researchers involved in the new study were able to document the viruses by analyzing their genetics, and by using advanced computational algorithms.

The study was the first to systematically sample the Arctic for viruses and it included deeper samples from other oceans than previously studied, Zayed said. A detailed accounting of these viruses is important because of their broad influence on other marine microbes, including bacteria, archaea, protozoa and fungi.

The new study was co-led by Zayed, Gregory and Matthew Sullivan, Ohio State professor of microbiology and civil, environmental and geodetic engineering.

"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," Sullivan said.

"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."

When viruses infect microbes, it can change the structure of the microbial communities, boost their metabolism and impact their evolution. In the oceans, that is linked to the oceans' ability to improve the environment by taking up human-produced carbon dioxide.

The researchers explored the genetic variation between individuals within each viral population, the level of variation between populations within each community, the level of variation between communities across multiple environments in the global ocean and the driving forces of all these variations.

"After 'drawing' these multilevel global maps of viral diversity, we found some surprises. First, almost all of the viral communities fell into just five groups based on their location and depth. 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," Gregory said.

The second surprise was that viral diversity was high in the Arctic Ocean. Most studies of larger organisms have concluded that diversity is highest at the equator and decreases as you move toward 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," Zayed said.

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