According to marine biologists led by Dr Kimberly Prather from the Scripps Institution of Oceanography, a factor that determines the properties of clouds that help moderate the planet’s temperature may be decided in the oceans.
Phytoplankton bloom in the Black Sea. Image credit: NASA / GSFC / Jeff Schmaltz / MODIS Land Rapid Response Team.
“It is exciting to finally be able to find a connection between microbes in seawater and atmospheric sea spray,” said Dr Prather, senior author on the study published online May 18 in the journal ACS Central Science.
Dr Prather and her colleagues found that the process by which marine bacteria consume phytoplankton has an apparent direct role in affecting cloud properties.
As the bacteria feed, phytoplankton break down into component molecules such as fats and lipids. The molecules the bacteria leave unconsumed can become airborne as the ocean’s surface churns.
Once in the atmosphere, these organic-enriched sea spray particles join dust and other particles in becoming the framework for the drops of moisture that ultimately congeal into clouds.
This conclusion comes nearly one year after the scientists created a replica ocean to observe in a controlled setting the types of marine particles that contribute to cloud formation and possibly human health issues once they become airborne.
In the lab, they recreated a phytoplankton bloom on a large experimental scale by importing 3,400 gallons of natural seawater from the California coast into a controlled ocean-atmosphere wave machine.
Their results show that variations in the dynamics between the various types of microbes affected the concentrations of less water-soluble species such as lipids in seawater. In turn, bursting bubbles from the waves launched these molecules into the atmosphere.
The study has provided a new understanding of the importance of the complex interactions between microbes in seawater and how they control the composition and cloud-forming ability of sea spray aerosol. Such information will help scientists build better climate models.
Among the cloud properties influenced by this microbial process is the clouds’ brightness. That brightness helps determine if solar energy is absorbed on Earth’s surface or reflected away from it, and thus influences temperature.
With the ability to generate sea spray aerosols in the laboratory during blooms, future studies will focus on developing a better understanding of the effects of biological compounds in sea spray 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.
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Xiaofei Wang et al. 2015. Microbial Control of Sea Spray Aerosol Composition: A Tale of Two Blooms. ACS Cent. Sci., published online May 18, 2015; doi: 10.1021/acscentsci.5b00148
