Microorganisms In Sea Spray Alter Ability Of Ocean To Seed Clouds
April 23, 2013

Microorganisms In Sea Spray Alter Ocean’s Ability To Seed Clouds

April Flowers for redOrbit.com - Your Universe Online

The ability of sea spray to form clouds over the ocean is influenced by ocean biology which alters the chemical composition of the spray. A team of scientists from the University of California, San Diego, is using a new approach to study tiny atmospheric particles called aerosols. These aerosols can influence climate by absorbing or reflecting sunlight and seeding clouds.

"After many decades of attempting to understand how the ocean impacts the atmosphere and clouds above it, it became clear a new approach was needed to investigate the complex ocean-atmosphere system — so moving the chemical complexity of the ocean to the laboratory represented a major advance that will enable many new studies to be performed," said Kimberly Prather, Distinguished Chair in Atmospheric Chemistry at the University of California, San Diego. Prather is also the director of the Center for Aerosol Impacts on Climate and the Environment.

When waves break, tiny bubbles form in the ocean and then rise to the surface to burst. The bursting releases gases and aerosols into the atmosphere. The new study, published in the Proceedings of the National Academy of Sciences, demonstrates that sea spray aerosols have a wide variety of shapes and sizes. The chemical complexity of these aerosols ranges from simple salts to complex biological mixtures to bacterial cells.

Scientists have studied how the chemical makeup of these aerosols affects their ability to take up water, seed clouds and react in the atmosphere for decades. In the real world, however, isolating and studying marine aerosols is difficult because aerosols from other sources overwhelm field measurements.

"Once the ocean-atmosphere system was isolated, we can systematically probe how changes in the seawater due to biological activity affect the composition and climate properties of the sea spray aerosol," said Prather, a professor in the Department of Chemistry and Biochemistry who holds a joint appointment at Scripps Institution of Oceanography.

To overcome this difficulty, seawater is pumped directly from the Pacific Ocean into a specially modified enclosed wave flume in the Hydraulics Laboratory at Scripps Oceanography. The air is stringently filtered within the wave chamber, allowing the team to eliminate contamination from other sources while probing the sea spray aerosol directly for the first time after it was produced by breaking waves.

The team systematically altered biological communities within the flume by adding various combinations of cultures of marine bacteria and microscopic marine algae, or phytoplankton over five days. Hydraulic paddles create waves by pushing water over an artificial shoal so that instruments positioned along the 108-foot long flume could measure the chemistry of the seawater, air and aerosols.

The aerosols showed a significant change in composition as the seawater changed and bacteria levels increased, leading to a reduction in their ability to form clouds. Specifically, one day after new cultures were introduced, bacteria levels rose fivefold and cloud-seeding ability fell by about a third. Even as the concentration of phytoplankton fell along with levels of chlorophyll-a, the pigment essential to photosynthesis, the changes were happening.

These results are particularly important since current estimates of biological activity in surface waters of the ocean rely on instruments aboard satellites that measure the color of the sea surface, which changes along with levels of chlorophyll-a.