"Rain and Snow May Be Created By Microorganisms, Scientists Report"
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 Feb. 29, 2008
Biological organisms play a significant role in the formation of rain and snow, according to a study released today by the journal Science.
Brent C. Christner from Louisiana State University and authors from France's INRA and Montana State University published the following in Science today:
We examined ice nucleators in snowfall from mid- and high-latitude locations and found that the most active were biological in origin.
Our results indicate that the biosphere is a source of highly active ice nucleators and suggest that these biological particles may affect the precipitation cycle and/or their own precipitation during atmospheric transport.
Microbes may be responsible for snow — and rain for that matter. They are certainly involved in much of the man-made snow that ski resorts use to cover for Mother Nature's winter lapses. Microorganisms, particularly bacteria, produce proteins in their cell walls that bind water—even if they are dead. In fact, they bind water in such an orderly fashion that water droplets freezing around a microbe almost mirror the natural lattice formation of ice. As a result, bacteria can help snow form at warmer temperatures than would otherwise be the case, which explains why some ski resorts add dead microbes to the mix in their snowmaking machines. And now scientists have discovered such biological precipitation catalysts in natural snows—in such far-flung locations as Montana and Antarctica.
Brent C. Christner posted the following on his website, "Certain plant-associated bacteria have the capacity to freeze supercooled water at temperatures as warm as –1° C, which is catalyzed by a protein in the outer membrane of the bacterial cell. Ice nucleating active bacteria are present at altitudes of several kilometers and have been documented in rain and snowfall. Based on the warm temperature and efficiency at which they function as ice nuclei, we hypothesize that these biotic particles have important impacts on atmospheric processes by serving as freezing catalysts in clouds, thus inducing precipitation."
The discovery of these organisms and their importance in the water cycle could help researchers improve climate forecasts and better understand the relationship between the biosphere and climate, the authors concluded.
They could also one day be used to bring rain to dry areas, said Christner.
Scientists have long known that the ice crystals in clouds which become rain or snow need to cling to some kind of particle, called ice nucleators, in order to form in temperatures above minus 40 degrees Celsius.
But they did not realize, until now, that the most active particles involved in this process are living ones, Christner said.
"Every snow and ice sample we've looked at, we found biological ice nucleators," he said in a telephone interview.
"Here's a component that has been completely ignored to date."
Biological ice nucleators were first discovered about 40 years ago by researchers trying to determine why some plants were damaged by frost and others were not.
They discovered that the plants which froze were covered in bacterial plant pathogens which are able to capture moisture in the air and turn it into ice at temperatures as warm as minus two Celsius.
Mineral ice nucleators like dust and soot can only capture and freeze the moisture at temperatures below minus about 10 degrees Celsius.
"It means that when cloud temperatures are in the range where inorganic matter are not active, these biological ice nucleators are active," Christner said.
Christner and his team have not yet determined how much precipitation is formed with these organisms.
But they found a stronger presence in snow collected from Montana and France than that collected in northern Canada and Antarctica.
These particles can be released by the sun's radiation or in the dust kicked up when farmers till the fields or even step on plants. They are then carried up into the atmosphere by wind.
The fact that they were discovered in Antarctic snow samples shows that they can be carried great distances, Christner said.
Excerpted from Science Magazine and Live Science |
