科学美国人60秒:Plankton Blooms Fuel Cloud Droplet Formation

The Southern Ocean, which surrounds Antarctica, is the cloudiest place on Earth. It’s relatively free of humans. And the dust, pollen and spores that float off more temperate lands don’t make it that far south—making the Southern Ocean an ideal lab to study the natural formation of clouds. 

"So this is a little bit like, if you want to hear someone talking, it's easier to hear them in a quiet room than in a room where a lot of other people are talking as well." Susannah Burrows is an atmospheric scientist at Pacific Northwest National Lab in Washington.

The isolated signal Burrows and her colleagues wanted to 'hear' was how particles from floating phytoplankton influence cloud droplet formation. They used computer models to simulate the stuff that seeds clouds over the Southern Ocean: particles like sea salt; organic bits from phytoplankton kicked up by sea spray; and sulfates, from the gases the critters emit.

They compared those particulate simulations to actual satellite measurements of clouds. And they found that during the southern summer, when plankton bloom, the phytoplankton may actually double cloud droplet formation. That in turn increases the reflectivity of the clouds, meaning more sunlight bounces back into space during the brighter summer months. 

Almost like the Southern Ocean slips on a pair of sunglasses, just when it gets too bright? "<laughing> That's an interesting analogy… um it's less like sunglasses and more like…" We later agreed—it’s more like the sunshade you unfold in your car in the summer months, to reflect hot sunlight back into the sky. The study is in the journal Science Advances. [D.T. McCoy et al, Natural aerosols explain seasonal and spatial patterns of Southern Ocean cloud albedo]

The goal, Burrows says, is to understand cloud formation, free from the influences of human pollution. "And that will help us to better understand the magnitude of changes in climate that are due to human impacts." And as the Arctic loses its ice—opening up a whole lot of new watery habitat for phytoplankton—she says the Arctic Ocean could someday have a cloudier forecast, too. 

—Christopher Intagliata