Plankton virus affects cloud formation

A species of marine phytoplankton that explodes after contracting a virus may play a role in regulating Earth’s climate, a new study finds.

Emiliania huxleyi is a type of single-celled plant-like organism called a coccolithophore that occurs ubiquitously in the world’s oceans. Under the right conditions, it multiplies rapidly to form giant aggregations, known as blooms, up to several thousand square kilometres in size.

When these blooms are infected by a virus called, imaginatively enough, the E. huxleyi virus (EhV), the coccolithophores burst. Their calcium carbonate exoskeletons, or coccoliths, are then scattered into the water column.

Pushed to the surface by bubbles, the exoskeleton fragments are aerosolised, or turned into airborne particles. Research published in the journal iScience by researchers at the Weizmann Institute of Science and Hebrew University of Jerusalem, in Israel, finds that in this state they may help promote cloud formation and potentially alter atmospheric processes.

The findings reinforce the idea that everything is linked in the Earth system, explains co-author Ilan Koren.

“Our experiments suggest that ocean ecology can strongly affect fluxes of biological particles to the atmosphere,” he says. “This study shows the huge potential of such links to be important.”

Marine aerosols are a key component of the planet’s climate system. However, previous studies have disagreed over the degree to which aerosol formation is influenced by localised marine microbial activity. Even less certain is how the interactions between microbial communities — plankton and viruses, for instance — affect the physical and chemical properties of the aerosols that are formed.

To explore this, a team of researchers led by Miri Trainic conducted an experiment. In the laboratory, they started with cultures of E. huxleyi in sea water. Half were exposed to EhV, with the other half kept as controls.

Within one day, the infected plankton quickly shed their exoskeletons, losing 25% more coccoliths than their uninfected counterparts. Over the next week of growth, the concentration of coccoliths in the sea water continued to rise for the infected E. huxleyi cultures, but not in the controls.

Next, the scientists used a bubbling system to measure how many coccoliths became aerosolised in the two groups. The results were similar to the growth experiment: coccolith concentrations in the aerosols of the infected samples were an order of magnitude higher than in the controls.

The coccoliths’ size and shape help explain why they are so readily airborne. Their large, plate-like structures means that they settle out of the atmosphere at a rate that the authors note, “is about 25 times slower compared with sea salt particles with the same dimension”.

By staying suspended for longer, the coccoliths increase the window of opportunity for chemical reactions within the atmosphere.

Moreover, coccoliths surpassed sea salt in terms of their contribution to volume and surface area in the aerosol. Although salt is the dominant inorganic component of marine aerosols, “coccoliths may be as important”, the researchers estimate, when it comes to atmospheric processes that rely on aerosol surface area.

The study is the first to show that large-scale atmospheric change may be attributable to feedbacks between microscopic organisms during bloom conditions.

Testing these processes on a bigger scale is important, says Koren: “The next challenge will be to better understand and quantify it in open oceans.”