“A lot of what we didn’t really ever see before in the ocean are predators and parasites, zombies and vampires that are floating through this incredible set of diversity, battling it out,” Dr. Palumbi said. “All these tiny little critters add up to something that is really a part of the way our planet operates.”

The vast genetic diversity of the oceans impressed many of the scientists involved in the Tara Oceans project, a consortium that involved 18 institutions.

The researchers identified roughly 40 million genes in the upper layers of the world’s oceans. The human gut microbiome, in comparison, is known to have only about 10 million genes, said Shinichi Sunagawa of the European Molecular Biology Lab in Heidelberg, Germany, who was a first author on one of the papers.

The raw data produced by the Tara expedition should allow scientists eventually to predict how microbial life will change as a function of changes in water temperature, said Eric Karsenti, a cell biologist and scientific director of the consortium.

One of the new papers tracks the effects warming waters have on bacterial diversity, suggesting that other microbes, like viruses and single-celled organisms, are probably affected as well. Future analysis should allow researchers to build predictive models for what will happen to microbial communities as water temperature changes, Dr. Karsenti said, and how much that will affect oxygen production and carbon dioxide absorption.

Life on Earth started in the oceans, so the Tara data also provides new insights into creatures directly descended from those of a billion years ago, Dr. Bowler said.

“By matching DNA-level information with what these organisms look like, we can learn more about them, more about how they work, and hopefully learn more about our own origins as well,” he said.