For the experiment, Prather’s team drew thousands of gallons of water from the Pacific into a long, enclosed tank in a lab, where the atmosphere had been carefully filtered so that the only microbes in it would come from the water. The researchers encouraged the organisms to grow, provoked wind and waves, and sampled furiously from the resulting spray. They performed a quick genetic test to identify what was in there, and found that indeed, not everything that lived in the ocean was making it out.

In particular, certain groups of bacteria were much more likely to rise into spray than others. Corynebacterium, of a type often found on the skin of people living around Prather’s university in San Diego, she says, was found to be more prominent in the spray than it was in the water, for instance. When the researchers dug into why, they found that these particular bacteria have cell-wall components that repel water. “These guys have waxy walls,” Prather says. “Of course they’re going to get out.” Viruses that were encased in fat-containing membranes managed to leave easily as well.

Now that the researchers have scratched the surface of what gets up into sea spray, the issue becomes whether these same microbes are the ones that have been found in clouds. Prather says that the organisms up there have not yet been fully identified, but gathering more samples with balloons or specialized planes is a plausible next step. The group also plans to repeat the sea-spray experiments using seawater from different times of year, or seawater inoculated with cultures of sea-going microbes from elsewhere in the world, to see how the results change.

Another route will be to pump in different amounts of carbon dioxide into the tube’s air to study the effects of the rising levels in Earth’s atmosphere. “One of the questions is, what happens to the microbes—what happens to all these processes—when you get to a more enriched CO 2 atmosphere? What happens when we hit 600 parts per million, which we will?” says Prather. “We want to do those experiments now, so we can predict where we’re going.”

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