After sunlight completes its eight-minute journey to Earth, white surfaces such as clouds bounce much of it back into space. The whiter and brighter the clouds, the better they reflect sunlight and keep the planet cooler.Now, a study has been published Atmospheric chemistry and physics examines a surprising part of this process: how tiny aquatic organisms known as phytoplankton play a big part in whitening the clouds on Earth.
Scientists used satellites to monitor large swaths of the Antarctic Ocean for five years. They found that clouds forming south of 60 degrees latitude, closer to the South Pole, tended to be noticeably whiter than those further north.
reason? Marine phytoplankton are tiny, says Gerald Mace, an atmospheric scientist at the University of Utah and lead author of the study. Antarctica is a “highly productive area” where small organisms such as phytoplankton thrive more abundantly than in the more northern oceans. Many of these sunlight-consuming organisms release a compound called dimethyl sulfide as part of their metabolism. This rises and reacts with gases in the atmosphere to form small aerosol particles and eventually clouds.
Meinrat Andreae, a biogeochemist at the Max Planck Institute for Chemistry, who was not involved in the new study, who first studied the ability of phytoplankton to seed clouds, says that water vapor They usually say that they must first bind to “seed” particles and condense into cloud droplets. South of latitude 60°, abundant phytoplankton produce dimethyl sulfide seeds so profusely that the clouds that form there are full of tiny water droplets.
In more northern regions, cloud-forming species are less common. “Mostly it’s just salt particles blown up by ocean spray,” says study co-author Sally Benson, an atmospheric scientist at the University of Utah. The resulting clouds contain more, fewer water droplets, giving them less surface area to reflect sunlight than the many smaller droplets in southern clouds, the researchers say.
The study also found that phytoplankton populations, measured by satellite observations of the green compound chlorophyll in water, peak each summer, followed by a peak in cloud reflectance. Although the role of phytoplankton in this process is a global phenomenon, Mace notes that its impact is most pronounced in the Antarctic, where plankton is abundant and human influence is low.
Phytoplankton have long been known to play a role in cloud bleaching, but existing climate models still lack sufficient data to fully explain their effects, Andrea said. . He added that a study of this scale — monitoring a large ocean area over five years — could help uncover new patterns, such as the strong link between cloud whiteness and latitude. “There’s no question that with a study of this size, we’ll be able to incorporate better information into our models,” he says.
