Tiny Plankton Brighten the Clouds Over and Cool the Southern Ocean

First Posted: Jul 20, 2015 07:37 AM EDT

What keeps our oceans cool? Marine plankton apparently does the job. Scientists have found that tiny ocean life in the vast stretches of the Southern Ocean cause clouds to be brighter and reflect more light back into the atmosphere.

"The clouds over the Southern Ocean reflect significantly more sunlight in the summertime than they would without these huge plankton booms," said Daniel McCoy, co-lead author of the new study, in a news release. "In the summer, we get about double the concentration of cloud droplets as we would if it were a biologically dead ocean."

Plankton actually produce airborne gases and organic matter. This, in turn, seeds cloud droplets, which lead to bright clouds that reflect more sunlight. The increased brightness over the Southern Ocean, for example, reflects about 4 watts of solar energy per square meter.

Clouds reflect sunlight based on both the amount of liquid suspended in the cloud and the size of the droplets. Each droplet actually grows on an aerosol particles, and the same amount of liquid spread across more droplets will reflect more sunlight. In the case of the Southern Ocean, clouds are composed of smaller droplets since plankton emits gas to form marine droplets.

"The dimethyl sulfide produced by the phytoplankton gets transported up into higher levels of the atmosphere and then gets chemically transformed and produces aerosols further downward, and that tends to happen more in the northern part of the domain we studied," said co-lead author Susannah Burrows. "In the southern part of the domain there is more effect from the organics, because that's where the big phytoplankton blooms happen."

The mechanisms roughly double the droplet concentration in summer months. This, in turn may tell researchers a bit more about how oceans cool themselves.

The findings are published in the journal Science Advances.