Seaweed makes clouds 01.08.2015

Clouds almost never dissipate over the Antarctic waters of the World Ocean, and the reason for this, as it turned out, is in phytoplankton - local microscopic algae literally make clouds, releasing aerosol particles into the atmosphere. Usually, when they talk about aerosols, they mean those that are obtained as a result of human activity (smoke from factory chimneys, etc.). Soot particles serve as a kind of "seeds" around which water vapor condenses - this is how drops are obtained that combine into a cloud.

But such condensation points can also have a completely natural origin: the smallest splashes of water containing organic substances and sea salt, or sulfates and ammonium salts as waste products of some living organisms. The fact that the sea and its inhabitants serve as a source of "natural aerosols" has long been talked about, but so far few people have tried to quantify the contribution of marine ecosystems to cloud formation. That's what Dennis Hartmann of the University of Washington, along with colleagues from the University of Leeds, Pacific Northwest National Laboratory, and Los Alamos National Laboratory, tried to do.

The work used data from NASA satellites, which made it possible to estimate the density of clouds between 35° and 55° south latitude. The state of the clouds was compared with the concentration of chlorophyll a, which usually serves as a marker of biological activity in the seas and oceans. In an article in Science Advances, the authors write that the relationship between clouds and chlorophyll levels was unambiguous: the more photosynthetic pigment (that is, the more algae) there was, the cloudier the weather was.

Life in the ocean increased the amount of cloud water droplets by 60% annually; The effect was most noticeable in summer. Clouds that are low above the earth reflect sunlight, and the surface of the planet below them will cool. (The "lock-in" of heat and the greenhouse effect are caused by other, high-level clouds.) In summer, the level of solar radiation increases, and at the same time, as was said, the concentration of phytoplankton increases - according to the researchers, algal activity leads to the fact that the amount of reflected solar radiation increases by 10 watts per square meter. This is comparable to what happens in the northern hemisphere, with the exception that in the north an additional "cloud reflection" occurs due to industrial pollution of the atmosphere.

How can microscopic algae increase cloudiness? The first way: releasing gaseous dimethyl sulfide, which in the atmosphere turns into a sulfuric acid residue - sulfate, which, in turn, condenses water vapor very well. The second way: due to organic residues rising into the air on the surface of the smallest bubbles that have come off the water. Such bubbles with organic additives can also serve as condensation centers for cloud droplets. It is curious that from 35° to 45° south latitude clouds over the ocean are formed mainly due to dimethyl sulfide, and from 45° to 55° - due to phytoplankton organic matter.

Thus, the assumptions about the active climatic activity of marine ecosystems were confirmed - tiny algae can really make clouds. We tend to believe that only humans are powerful enough to make a big impact on the climate, but as we can see, the current state of affairs can be more complicated. (And not only because of phytoplankton - here we can also recall the work of employees of the University of Göttingen, published last year in Angewandte Chemie: it describes how ordinary conifers help form clouds with the help of substances contained in their resins.) By building climatic model, trying to assess our impact on the weather on the planet, we must also take into account the contribution of natural producers of cloud-forming aerosols.