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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.

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Feeling the Heat: The Climate Challenge

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Feeling the Heat: The Climate Challenge
Get the facts on the world's hottest topic How will global warming impact your life? Discover the answers through interactive activities for all ages at Birch Aquarium at Scripps's newest exhibit opening Saturday, May 19, 2007.