In a wooden building overlooking the Pacific Ocean, 3,800 gallons of seawater empty into a long, clear, covered tank—a wave machine.
On one side of the 33-meter-long flume is a mechanical paddle, working like a kid in a bathtub to push water forward. The water builds into a wave that breaks on the machine’s “beach,” a board representing the coastline. As the broken wave falls, bubbles burst, producing sea spray particles that are sucked up into sampling tubes.
Analyzing these particles has let a team of scientists gain insights into how microbes in ocean water control the ability of sea spray droplets to serve as “seeds” for clouds.
The work, which appears in ACS Central Science, also demonstrates how changes in the ocean can influence changes in the sky. The research is expected to help researchers build better climate models.
Sea spray is composed of bubbles of ocean water carrying sea salt, bacteria, viruses, and complex organics like proteins, fats, and sugars.
“When you change that composition, you start to change the ability of these particles to take up water and grow into cloud droplets,” says project collaborator Chris Cappa, an associate professor in the University of California, Davis, department of civil and environmental engineering.
The research team used the wave machine at UC San Diego’s Scripps Institution of Oceanography to recreate a phytoplankton bloom on a large experimental scale.
What does phytoplankton have to do with sea spray? Lots.
The phytoplankton itself doesn’t end up in sea spray. However, as it grows and dies, it produces molecules that can become part of the sea spray droplets when waves break, a process that was previously poorly understood.
The study finds that a critical factor that controls the concentration of these molecules in sea water is their destruction by ocean microbes. This in turn affects the chemical composition of sea spray particles and helps determine how and if the particles can act as cloud seeds.
“It’s this combination of production and destruction of these key molecules that ultimately determines the influence of sea spray particles on clouds and global climate,” Cappa says.
The study has provided a new understanding of the importance of how microbes in seawater control the cloud-forming ability of sea spray aerosol, says lead author Kimberly Prather, a UC San Diego chemistry professor and director of the Center for Aerosol Impacts on Climate and the Environment.
The study received funding from the National Science Foundation through the Centers for Chemical Innovation program.
Source: UC Davis