The world's oceans teem with scientific mystery, unknowns that could prove to be tools that will one day protect the planet from global warming. Researchers report they've tripled the known types of viruses living in waters around the globe, and now have a better idea what role they play in nature. The study, led by scientists at The Ohio State University, appears in the journal Nature.

Their work will likely have far-reaching implications, including ultimately helping to preserve the environment through reducing excess carbon humans put into the atmosphere, they say. The oceans currently soak up half of that carbon, but that comes at the cost of acidifying the oceans, which puts some ocean-dwellers, including shellfish, at risk. Understanding how microbes and viruses interact is critical to any possible management efforts, the researchers say.

Their work was possible because of the unprecedented three-year Tara Oceans Expedition, in which a team of more than 200 experts took to the sea to better understand its unseen inhabitants, and the Spanish-led 2010 Malaspina expedition, which evaluated the impact of global change on the ocean and studied its biodiversity. Researchers at Ohio State processed viral samples collected by scientists aboard the two ships.

Lead author Simon Roux analyzed genetic information from those samples to catalog 15,222 genetically distinct viruses and group them into 867 clusters that share similar properties. Roux is a postdoctoral researcher in the lab of Matthew Sullivan, the study's senior author and associate professor of microbiology at Ohio State.

"Ten years ago I would never have dreamed that we could establish such an extensive catalog of ocean organisms around the world," Sullivan said.

"Scientists around the world are revealing how microbes impact our bodies, soil, the air and the oceans. As we improve our ability to study viruses, we're seeing the role viruses play in these microbial functions," he said.

Roux said microbes in the oceans make half of the oxygen humans breathe, making viruses that infect these microbes particularly important.

"Our work not only provides a relatively complete catalog of surface ocean viruses, but also reveals new ways that viruses modulate greenhouse gases and energy in the oceans," he said.

At any given time, about one in three cells in the ocean are infected with a virus, altering the way the cell behaves, Roux said.

Infection is always bad news for the cell because it impedes its function in some way. But it's not always bad news for the environment. Viruses likely play a key role in ridding oceans and lakes of harmful algal blooms, for instance.

The Ohio State team is eager to see how viruses might fit into future efforts to reduce carbon in the atmosphere.

Greenhouse gases threatening the environment could be mediated by these viruses through manipulation by scientists - something that is at least a couple decades off, but will likely be necessary to manage climate change, Sullivan said.

"The ocean is a major buffer against climate change. Our suspicion is that people will leverage this buffer to their benefit," he said. "They could find ways to fine-tune viruses so that they sink carbon into the deep ocean."

Prior to this work, viruses were identified here and there around the world, he said. That previous list - most recently outlined in prior work by the Sullivan Lab - was used for comparison in this study.

Now, Roux and Sullivan think they have a much more complete picture of what's happening on a viral level in the world's marine waters.

"Simon has developed amazing tools for understanding these viruses," Sullivan said, adding that this work will serve as a blueprint for other researchers, including those studying viruses outside the ocean.

Roux used a jumble of genetic data, called "metagenomes," to arrive at his catalog of viruses.

"The magic is being able to piece these things together," he said, adding that recent developments in bioinformatics and sequencing technologies made this work possible.

Once he put the puzzles together, Roux was able to identify genetic similarities and categorize the viruses.

"Because of this work anyone who studies viruses - in humans, soil, the air will better know how to identify and classify what is there," he said.

Other Ohio State researchers who worked on this study were Jennifer Brum and Natalie Solonenko.