Scientists discovered that ocean life is responsible for over half of the summer cloud cover over the southern ocean.
A team of researchers used a combination of satellite data and computer modeling to demonstrate how microparticles, including aerosols, that are emitted by marine organisms can more than double summer cloud droplet numbers around Antarctica, Pacific Northwest National Laboratory reported.
This increased cloud cover raises the amount of sunlight that is reflected back into space. The recent study is also the first to estimate how much solar energy is related to the entire Southern Ocean.
"It is a strong effect," said climate scientist Susannah Burrows at the Department of Energy's Pacific Northwest National Laboratory. "But it makes sense because most of the area down there is ocean, with strong winds that kick up a lot of spray and lots of marine microorganisms producing these particles. And continental aerosol sources are mostly so far away that they only have a limited impact. Really the marine aerosols are running the show there."
The Southern Ocean is one of the cloudiest places on Earth, and these clouds could help scientists determine how sensitive our planet is to atmospheric greenhouse gas concentrations. In order to accomplish this, researchers must gain insight into how aerosol particles brighten clouds. These particles arise from vegetative matter, sea salt, and dust, but studying the impact of natural aerosols has been difficult because they are generally overpowered by those released by man-made pollution.
To distinguish between aerosols from different sources, the researchers used computer models to simulate both organic matter and sulfates, including sea salt. They also used a new set of satellite measurements of cloud droplets.
"Satellite data allows us to observe events that occur over the course of months and on a scale of thousands of kilometers in the remotest regions on the planet," said co-author Daniel McCoy, of the University of Washington. "It really gives us an unparalleled glimpse of the Earth System's complexity."
The groundbreaking computer model simulated the presence of organic matter within sea spray, instead of the aerosols themselves.
By comparing three sources of aerosols, the researchers determined the aerosol concentrations given off by marine organisms almost doubled the cloud droplet concentration in the summer. This was estimated to increase the amount of sunlight reflected back into space by about 4 watts per square meter a year.
"Phytoplankton in the oceans are a really important source for cloud-droplet-forming aerosols in remote marine air, and we can see the effect they have on clouds is big," Burrows said. "Southern Ocean clouds play a large role in the global climate, and hopefully this will help us get a better sense of how sensitive the Earth is to greenhouse gases."
The findings were published in a recent edition of the journal Science Advances.
