Research Highlight: Innovative Aerosol Chemistry-Climate Study Achieves Full Bloom


Researchers at Scripps Institution of Oceanography and the Department of Chemistry and Biochemistry at UC San Diego succeeded in creating the largest phytoplankton bloom in a wave flume in history as part of a groundbreaking experiment to understand the effects of natural particles on the atmosphere.

The Center for Aerosol Impacts on Climate and the Environment (CAICE) cultivated the algae over the course of several weeks in July in a wave tank on the Scripps campus that enables them to observe ocean-atmosphere exchange processes in a controlled environment. Observations of the chemical composition of seawater and the atmosphere as the bloom evolved could break new ground in the understanding of how aerosols – tiny bits of living and inorganic matter – influence aspects of climate, especially cloud formation.

“On this scale, with 3,000 gallons of water, in a wave flume with breaking waves, this has never been done to our knowledge,” said CAICE Director Kim Prather, a distinguished chair in atmospheric chemistry at UC San Diego.

The experiment, called Investigation into Marine PArticle Chemistry and Transfer Science or IMPACTS, gave researchers the chance to do something that would be nearly impossible in the field: to observe everyday natural processes in the ocean while controlling variables such as nutrient quantity and wave action. IMPACTS data could help establish a baseline of how the oceans influence climate, independent of the effects they have when combined with the pollutants produced by human activities.

The scientists spiked natural seawater with inorganic nutrients, which led to a bloom of diatoms, common components of the ecosystems of surf zones where people swim and waves, as they churn seawater, eject particles into the air. Throughout the bloom progression, they were able to replicate biological interactions as they occur in nature and observe a complete microbial loop, a sequence through which organic carbon moves through food webs. The experiment was funded by the National Science Foundation which funds CAICE through the Centers for Chemical Innovation program.

Bits and pieces of this biological mix get airborne as waves break and bubbles burst leading to the production of sea spray. These ocean-derived aerosols rise into the atmosphere with some becoming the scaffolding of clouds, each particle becoming the nucleus onto which water vapor clings and ice crystals form. 

“Using this new ocean in the lab approach, we can measure all the parameters in the seawater and at the same time study the composition of particles that make it into the atmosphere over the course of a bloom,” Prather said.

How clouds form and whether they will produce rain have been difficult to predict and simulate in computer models. Understanding how sea spray affects cloud properties and precipitation could transform researchers’ overall understanding of Earth’s energy budget and how rapidly natural processes are affecting our climate.

Charlotte Beall, a first-year graduate student at Scripps, was one of several who spent 12 hours or more working on the experiment per day during the most intensive phases of the experiment. IMPACTS could help researchers understand which particles leave the ocean and how they have evolved by the time they reach the levels of the atmosphere at which clouds form, she said.

“No one’s even approached these kinds of questions in a laboratory setting,” said Beall. “The biggest gap in climate change models is uncertainty in cloud formation.”

Inducing biological processes to occur on such a grand scale in a lab setting represented a major challenge. The biggest obstacle of the experiment was successfully coaxing a phytoplankton bloom in a large tank while producing representative concentrations of viruses, bacteria, and phytoplankton. Prather’s team experienced numerous failed attempts before the July experiment worked. Prather said the features of the wave tank, housed at the Scripps Hydraulics Laboratory, helped make the experiment achievable. The design of the tank, which generates waves mechanically, enabled the researchers to create a closed system in which they could accurately measure a wide range of variables.

“It is a unique facility and was truly enabling of our research,” Prather said. “Adding a lid to the flume and sampling the air inside really allows the interdisciplinary studies that are needed by atmospheric chemists, oceanographers, and marine biologists.”

At present, even the impacts of biological components on the atmosphere and climate are largely unknown; CAICE scientists point out that only about 10-15 percent of the biologically derived organic compounds in the ocean have been identified.

Camille Sultana, a graduate student with Prather in UC San Diego’s Department of Chemistry and Biochemistry, said the experiment entailed long days, “15 hours minimum,” of “keeping the wave flume happy and everything running so data could be collected.”

“Our data are very complicated so it’s going to take a while to tease it all out,” said Sultana. 

One of the many applications of IMPACTS findings could be a better understanding of the effects of biological compounds on human health. Given that the biological compounds are inhaled by beachgoers and residents of coastal communities every day, their impacts could be substantial, but as of yet these effects are unclear. 

Besides UC San Diego researchers, among them microbiologist Farooq Azam, whom Prather credited with helping in the ultimate successful production of a bloom, IMPACTS included scientists from the University of Iowa, University of Wisconsin, University of the Pacific, Cal Baptist College, UC Davis, and Colorado State University.

“We have developed this new way of isolating the ocean-atmosphere system in the laboratory which gives us a new set of eyes on a very old problem,” she said.  “The next challenge will be unraveling how seawater changes our atmosphere and climate. We have now measured the progression of a bloom at realistic ocean concentrations and carefully tracked the chemistry in several compartments – seawater, sea surface microlayer, and sea spray aerosol.  The major challenge in the coming months will be to take this massive dataset and unravel the transfer processes of chemical components from one compartment to another, ultimately probing how this chemistry leads to changes in cloud properties.”

– Robert Monroe


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