No Two Sea Spray Bubbles Are the Same

Sea spray bubbles may be tiny, but they have a big impact on climate and no two are the same.

Sea spray holds tremendous power beyond its ability to drench beachgoers. Sea spray aerosol — the vapor produced by the spray’s bursting bubbles — helps to connect the world’s oceans to the atmosphere and affects climate. The aerosol’s components can travel hundreds of miles, and have even been found in the middle of the US, far away from any ocean.

New research published in the journal Chem has identified yet another unique aspect of sea spray: No two bubbles within its foamy whiteness are the same. Every element, from trapped gases to particulate matter, can differ from one bubble to the next.

Senior author Vicki Grassian said sea spay is produced through a bubble bursting mechanism that releases particles into the air as well as gases, such as nitrogen and oxygen, which are the main components of air. Grassian is co- co-director of the Center for Aerosol Impacts on Climate and the Environment at the University of California, San Diego.

“Other gases at much smaller concentrations can also get into the air,” she said. “In our study, we focused on the particles.”

Some of these small particles come from salts, fatty acids, carbohydrates, molecules secreted by microscopic ocean plants known as phytoplankton, and bacteria that feed on these tiny plants. The “smell” of the ocean is largely the odors given off by these many components. 

Grassian, lead author Richard Cochran, and their colleagues sought to study sea spray aerosol particles at various points during phytoplankton blooms, which can cover hundreds of miles of ocean. They didn’t need to sit around on beaches for months, though, waiting for a bloom to occur.

Instead, the scientists used a state-of-the-art experimental ocean housed at the Scripps Institution of Oceanography on the UC San Diego campus. Every detail of the miniature laboratory ocean, from its waves to creatures living within the water, can be fully controlled. This allows researchers to focus on individual processes and to tease apart one effect from another, such as natural versus human-caused climate change.

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“Chemists involved in the center were able to replicate the complexity of the ocean by working with physical oceanographers and marine biologists,” Grassian said, adding that the team managed to reproduce two phytoplankton blooms in the faux sea.

 “These blooms differed in the composition of sea spray ejected into the atmosphere,” she said, “and we attribute that to the fact that there are different levels of bacteria in the sea water during these two blooms.”

The scientists next measured how the individual particles retained moisture, a property called hygroscopicity. They found that the average amount of water taken up by the particles differed between the phytoplankton blooms. As the particles mixed with the various chemicals present in the sea spray vapor, they often became less able to carry water away from the experimental ocean.

“We discovered that the critical and overlooked component to this cycle is the role of bacteria, which are naturally efficient at transforming organic matter from phytoplankton,” Cochran said.

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Hygroscopicity is key to the cycle because, without water in the atmosphere, there would be no clouds, and therefore no precipitation. The continual release of water into the atmosphere via sea spray vapor helps to drive the necessary link between the oceans, atmosphere, and climate.

“It’s important to understand the impact natural processes have on the climate so we can build up a more accurate picture of climate change,” Grassian said in a statement.

She and her colleagues next plan to investigate how sea spray evolves as it interacts with sunlight and pollutants such as ozone, nitrogen oxides, soot, and ash.

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