Once airborne, seafloor bacteria may become seeds that promote the growth of ice crystals, an important step in the formation of Arctic clouds.
“Clouds are super important in the Arctic,” said Jessie Creamean, an atmospheric scientist at Colorado State University and lead author of new research published in mid-July in Geophysical Research Letters.
“They regulate the surface and atmospheric temperatures, affecting sea ice, ecology, shipping, Arctic climate and weather. And we just have a really poor understanding of how they form,” Creamean said.
Prior research from the Southern Ocean as well as laboratory experiments suggest that ocean microbes can enhance cloud formation. To investigate whether that holds true in the Arctic, Creamean and several of her co-authors embarked on a NOAA-funded research cruise through the Bering and southern Chukchi seas from late August to mid-September 2017. Over the course of several weeks, the researchers collected samples of seawater and aerosols suspended about 20 meters (66 feet) above the ship.
They measured the abundance of what are known as ice-nucleating particles, which seed clouds. They also took stock of seawater chemistry and chlorophyll concentrations, an indicator of phytoplankton abundance.
At first, Creamean said, she simply was hoping to get a baseline sense of the distribution of cloud-seeding particles in the ocean and atmosphere. But on Aug. 29, as their ship passed through the Bering Strait, the researchers measured particularly high levels of them. Through a combination of DNA analysis and microbial culturing, they determined that the airborne particles were mostly bacteria.
The researchers knew there was a big late-summer phytoplankton bloom underway about 150 miles to the south, and that they were in a region where phytoplankton that are transported north via currents tend to die, sink and become food for hungry bacteria.
After examining a number of oceanographic measurements and running their data through computer models, the researchers concluded that powerful winds associated with recent storm activity had stirred up the ocean, bringing some of these bacterial grazers to the surface, where they could be kicked up into the air.
The study doesn’t demonstrate that bacteria are forming clouds — simply that they’re making it into the atmosphere. But Creamean believes it’s a distinct possibility that some oceanic bacteria are reaching high enough altitudes to play a role in cloud formation.
“In the Arctic, clouds can be very low — down to 100 meters,” she said. “It’s very possible these things can interact with clouds.”
This is hardly the first paper to suggest Earth’s smallest organisms may have an impact on the weather — in fact, research into bioprecipitation dates back to at least the 1980s. Over the years, studies have suggested that microbes and their debris can brighten clouds, supercharge snowstorms and help create some of the biggest hail events.
With the advent of new genomic tools, scientists are learning that there are entire microbial ecosystems wafting through the lower atmosphere and that some hardy bugs are even eking out a living in the stratosphere. It’s possible we’re just scratching the surface of their weather-making potential.
As far as Creamean’s new Arctic observations go, the regional weather in late August 2017 supports her explanation for the bacteria-spiked air, said Xiangdong Zhang, an atmospheric scientist at the International Arctic Research Center who wasn’t involved with the new study.
At that time, he said, there was a well-developed high-pressure system over the East Siberian Sea, complemented by a low-pressure system over Alaska.
“The short distance between these systems results in large pressure gradients and then large northerly and northeasterly winds to blow over the Chukchi Sea and the Bering Strait,” Zhang wrote in an email. “The large winds definitely increase ocean mixing and bring bottom materials to the surface.”
It’s still early days for this research. But if ocean microbes do play a role in Arctic cloud formation, Creamean wonders how climate change could impact it.
Longer ice-free periods and warmer ocean waters are favoring the proliferation of phytoplankton in many parts of the Arctic. At the same time, some research suggests the Arctic could become stormier as sea ice recedes, perhaps enhancing Creamean’s seafloor-to-sky microbial pump.
Creamean is now collecting more data aboard the German icebreaker Polarstern as part of the year-long MOSAiC mission to the Arctic Ocean.
Given the rapid changes the Arctic is undergoing, it’s more important than ever to tease out the complex interactions between biology, oceans, ice and the atmosphere, she said.
After all, what happens in the Arctic doesn’t necessarily stay there.