Research Highlight: The Cloudmakers

Your beach vacation has officially begun when the first grains of sand grind between your bare toes and you breathe in that first rush of zesty salt air blown in from the ocean surface.

That mix filling your lungs is a more complicated brew than mere air and sodium chloride particles, as a team of Scripps Institution of Oceanography at UC San Diego researchers is discovering. The diverse team is beginning to understand a quality of the ocean that was scarcely measurable before now thanks to their unusual collaboration and the availability of cutting-edge technology.

Using seed money awarded by UC San Diego Chancellor Marye Anne Fox to encourage interdisciplinary collaborations between researchers across campus, the team is identifying and quantifying the kinds of particles besides salt crystals that get launched into the atmosphere via bubbling action at the ocean’s turbulent surface. The ocean is known to be a source of atmospheric particles called aerosols. In ways now beginning to be understood, however, the ocean also transports organic material such as proteins and carbohydrates and actual marine microbes. Winds blow these bits of matter into the atmosphere after breaking the surface as bubbles pop. The nature of the bubbles themselves seems to facilitate the elevator ride to the surface for certain organisms.

The team, led by atmospheric chemistry professor Kim Prather, who holds a joint appointment in the Center for Atmospheric Sciences at Scripps and in UC San Diego’s chemistry department, is especially interested in the microorganisms and how the chemical compounds they produce in the ocean influence atmospheric chemistry above the oceans. Those compounds could be key components of cloud formation over the open ocean. If Prather’s group can understand that relationship, it could help improve the basic tool of climate prediction, the computer model, allowing scientists to more accurately portray marine cloud characteristics and how in turn they might be affecting conditions in an era of human-caused climate change. 

“We are interested in marine aerosols and what’s getting ejected from the ocean. How does biological activity in the ocean affect cloud formation?” Prather said. “Can we get a handle on that because if we can, that’s 73 percent of the surface of the Earth we can now understand.”          

PRODUCTIVE SEAS, UNPRODUCTIVE CLOUDS?

Clouds need scaffolding to assemble themselves into fluffy masses of water droplets and ice crystals. Over land, dust and pollution blown skyward serve as the nuclei around which water droplets condense en masse. Over oceans, sea salt particles, the most common natural particles in the atmosphere next to dust, provide that service. The chemical composition of the dust or salt particles in large part determines if cloud droplets will become large and therefore conducive to creating rain or smaller droplets that are associated with dry clouds.

Rarely do tiny salt crystals rise into the atmosphere in a pure form. Various minerals and microbes such as bacteria and viruses and the organic compounds they produce often attach to the salt particles. Some microorganisms appear to have a special affinity for bubbles near the surface of the ocean and are able to hitch rides on the surfaces of the bubbles that rise and burst at the surface, releasing microbes such as cyanobacteria into the air.

This mix of tiny creatures and their chemical byproducts alters the chemistry of salt and influence what kinds of clouds salt aerosols create. Prather’s group has been looking for patterns, exploring whether aerosols influence cloud formation differently in different regions of the ocean and whether fluxes in biological activity at the surface of the ocean determine if the cloud forming overhead will bear rain or not.

To understand what’s going on, Prather uses an unusual tool invented in her research group called an aerosol time-of-flight mass spectrometer, a machine capable of inhaling air samples and identifying individually the millions of particles that pass through it. (See “The Dust Collector,” Summer 2004 Explorations.) In addition, she has enlisted a diverse group of scientists from across the Scripps campus for help. As a group, their work covers every aspect of the feedback loop in which clouds affect biological activity in the oceans and the activity in turn affects cloud formation.

Marine geochemist Lihini Aluwihare brings her expertise in the sequestration of carbon, one of the most important particles in the ocean. Marine biologist Brian Palenik can help identify what kinds of microbes and organic products are likely to become riders in the sky. Lynn Russell, an atmospheric chemist like Prather, will use mass spectrometry and infrared spectroscopy to acquire datasets complementary to Prather’s own. Each researcher has his or her own interest in the subject and the innovative methods being used to investigate it.

“There are a lot of questions in my field about what actually forms particles,” said Aluwihare. “(Prather’s) technique definitely gave us insight into that and could really give us more.”

Prather said it’s possible that even genomics experts at the J. Craig Venter Institute might become collaborators. Their specialized knowledge could show that some bacteria are more genetically equipped to adhere themselves to bubbles than others, having developed an adaptation that allows them to travel by leaving the ocean the way dandelion filaments on land are spread by winds to populate new areas.

BURSTING YOUR BUBBLE

Currently Meagan Moore, a second-year graduate student in Prather’s UC San Diego lab, is studying the transition of particles from water to air in a lab setting before replicating experiments in the field. Using mason jars of collected seawater, she is studying the effects of chemical compounds called surfactants that tend to collect at the surface microlayer, the “skin” of the ocean that’s only micrometers thick. In early results, she has found that a surfactant called oleic acid seems to stifle the production of cloud-creating aerosols.

In the same lab, project scientist Hiroshi Furutani, credited with coming up with the thesis that launched the project, is studying what kinds of organisms tend to get ejected with sea salt. He has found that the journey from ocean to air can increase the concentration of particles 50 to 100 times. In a recently completed research paper, he and Prather report that organic matter seems to have an easier time leaving seawater through bubbles than through atomizing actions that are more typically associated with discharges through sea spray.

Furutani has also found that smaller organisms such as viruses tend to be especially concentrated when ejected into the air. Evidence like that is spurring Prather to see if cloud-making microbes also have a human health side effect. She is interested in exploring possible links between respiratory health and episodes in the ocean like sewage spills or algal blooms. In early April, the Unified Port of San Diego awarded her a grant to use her group’s recently developed mobile lab to study air pollution in the San Diego Bay region.

“It’s definitely something to think about,” Prather said. “There are large numbers of asthma sufferers in San Diego with our supposedly clean air and this could be a part of it. At this stage, no one knows for sure.”

WARM UP TO THE SCIENCE OF  ‘FEELING THE HEAT’

The more accurate scientific data are, the better the game plan to respond to global warming can be. Now Scripps Institution of Oceanography researchers are taking one of the least understood variables of climate — the role of particulate pollution and other particles in controlling climate — and creating the most comprehensive analysis of airborne particles to date.

Besides being a source of air pollution, aerosols ranging from soot to dust can also hamper precipitation and influence the amount of sunlight reaching Earth’s surface on broad scales. In a project sponsored by energy giant BP, Lynn Russell and Kim Prather are beginning to more deeply analyze multiple aerosol datasets that their groups have collected around the world in an effort to provide better input into models and reduce some of the uncertainties associated with how aerosol size and chemistry influence climate change.

Visitors to “Feeling the Heat: The Climate Challenge,” a new exhibit at Birch Aquarium at Scripps opening May 19, will be able to learn more about the aerosol research going on at Scripps along with other cutting-edge climate work taking place here and elsewhere.

“Aerosols can cool the planet and they can warm the planet,” Prather said.   “We’re trying to educate the public that there’s more out there than CO2 affecting our climate.”