Researchers Identify Cloud-Seeding Algae

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Researchers from National Oceanic and Atmospheric Administration (NOAA) in Boulder, Colorado suggested that an algae-killing virus may be helping seed the skies with clouds.

Emiliania huxleyi is a single-celled alga whose blooms can cover thousands of square kilometers of ocean. Along with other photosynthetic microbes, the organism occupies the base of the food web in most of the world’s seas. These organisms have shells made of calcium carbonate plates called coccoliths. The shells fall apart when these organisms die and these coccoliths are accumulated on the ocean floor with silt and other materials. These shells turn into sedimentary rocks over time. However, some of these coccoliths are cast into the air by breaking waves or popping bubbles. Now, the research by National Oceanic and Atmospheric Administration (NOAA) reported that these organisms provide the kernel for water vapor to condense and form droplets, which in turn become clouds. The research was published in iScience on August 17, 2018.

The coccoliths are found among the particles in sea spray and scatter light producing haze. However, the particles provide surfaces where water vapor can condense. Organisms such as E. huxleyi get wiped out in much larger numbers as the organisms die naturally or through viral infection. The researchers analyzed the organisms in lab to better understand whether and how the numbers of airborne coccoliths might fluctuate over time. Moreover, the researchers wanted to determine that mechanism of E. huxleyi virus (EhV) that might change the numbers of free-floating coccoliths in their seawater tanks and in the air above.

Each milliliter of water held around 20 million free-floating coccoliths at the start of the tests. However, when the algae was infected with EhV after five days, the number of tiny plates in the water tripled and  they had grown by nearly 10-fold in the air above the water. This suggested that airborne coccoliths may play an important role in cloud formation above the oceans. Moreover, the tiny particles provide a lot of surface area in large numbers resulting in condensation of water vapor to form droplets. The number of coccoliths readily grow once these shells begin to make their way into the atmosphere.

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