Life in the clouds? Climate science yields biological clues

How was terrestrial life carried to the remote Hawaiian Islands?

How was terrestrial life carried to the remote Hawaiian Islands?

Cloud researchers have identified a new transport mechanism—ice crystals in clouds.

Biologists have a short list of mechanisms for getting land-based life forms across more than 2,000 miles of ocean to the Islands: drifting on the sea, either as floating seeds or perhaps riding on big pieces of debris, like trees; on the wing, like birds that fly here, and seeds or tiny snails stuck to those birds, and even in bird poop—seeds of things they ate before taking flight; and generally, blowing in the wind—the assumed vehicle for fern spores.

Whichever techniques were employed, they worked. By the time the first humans arrived, the islands were carpeted in life—plants, birds, fungi, snails, butterflies, all kinds of life.

The latest piece of evidence for how those things got here came out of climate research. Scientists trying to learn about cloud formation went up and sampled clouds in the air, and analyzed the cloud ice crystals while still in flight.

Science has long known that dust particles can be found at the core of raindrops. But reporting in the May 17 online journal Nature Geoscience, scientists said that for the first time they found that there's also biological material at the heart of cloud ice crystals.

The paper is “In situ detection of biological particles in cloud ice-crystals,” by Kerri A. Pratt of the Department of Chemistry and Biochemistry, University of California, San Diego; along with co-researchers Paul J. DeMott, Jeffrey R. French, Zhien Wang, Douglas L. Westphal, Andrew J. Heymsfield, Cynthia H. Twohy, Anthony J. Prenni and Kimberly A. Prather.

The work was done over Wyoming aboard a C130 aircraft operated by the NCAR, the National Center for Atmospheric Research. The ice they were inspecting over Wyoming had particles originating in Asia—suggesting they could have passed near Hawai'i to get to North America. (It has long been known that Asian mineral dust can arrive in Hawai'i on the wind.)

The researchers were trying to learn more about clouds, to help advance climate change research.
They collected ice crystals from non-precipitating clouds, melted them in flight, and studied their contents. While half contained mineral dust, close to a third contained biological material. It included bacteria, pollen and fungi.

Since the biological material was destroyed in the testing, they were unable to determine whether it was alive and capable of surviving when it eventually was rained down onto the land again.

For the climate researchers, the interesting thing is that biological materal may form the “seeds” for cloud droplets, although some microbes may also have burrowed into dust particles that became cloud seeds.

Such work could be done on the ground with raindrops and snow flakes, but there is the possibility that microbes could have been picked up on the way to the ground, rather than having been the droplet seed.

“These were non-precipitating clouds. In theory, one could collect rain and snow and look for microbes and in fact people have done this in the past. The challenging issue in doing this is the microbes could be airborne and just scavenged via the fall by rain drops as opposed to having served as the nuclei themselves,” said co-author Kim Prather via email.

The work also suggests a new means of transport for the “seeds” of life to the distant corners of the world—like Hawai'i.

© Jan TenBruggencate 2009