Study shows bacteria are common in snow
Those beautiful snowflakes drifting out of the sky may have a
surprise inside - bacteria. Most snow and rain forms in chilly
conditions high in the sky and atmospheric scientists have long known
that, under most conditions, the moisture needs something to cling to in
order to condense (become more solid).
Now, a new study shows that a surprisingly large share of those
so-called nucleators turn out to be bacteria that can affect plants.
"Bacteria are by far the most active ice nuclei in nature," said
Brent C. Christner, an assistant professor of biological sciences at
Louisiana State University.
Christner and colleagues sampled snow from Antarctica, France,
Montana and the Yukon and reported their findings in the journal
Science.
In some samples as much as 85 per cent of the nuclei were bacteria,
Christner said in a telephone interview. The bacteria were most common
in France, followed by Montana and the Yukon, and were even present to a
lesser degree in Antarctica.
The most common bacteria found was Pseudomonas syringae, which can
cause disease in several types of plants including tomatoes and beans.
The study found it in 20 samples of snow from around the world and
subsequent research has also found it in summer rainfall in Louisiana.
The focus on Pseudomonas in the past has been to try and eliminate
it, Christner said, but now that it turns out to be a major factor in
encouraging snow and rain, he wonders if that is a good idea. Would
elimination(getting rid) of this bacteria result in less rain or snow,
or would it be replaced by other nuclei such as soot and dust?
"The question is, is it a good guy or a bad guy," he said, "and I
don't have the answer to that."
What is clear is that Pseudomonas is effective at getting moisture in
a cloud to condense, he pointed out. Killed bacteria are even used as an
additive in snow-making at ski resorts.
Which raises the question, Christner said, of whether planting crops
known to be infected by Pseudomonas in areas experiencing drought might
help increase precipitation (rain) thereby adding more nuclei to the
atmosphere.
It has been known that microbes and insects and algae blow around in
the atmosphere, Christner added, "but the atmosphere has not been
recognised as a place where things are active. That has been changing in
the last decade. In a cloud you've got water, organic carbon,"
everything necessary to support a microorganism.
Virginia K. Walker, a biologist at Queen's University in Kingston,
Ontario, Canada, said other researchers have found bacteria serving as
snow nuclei, but had not identified it as Pseudomonas.
"It's one of those great bacteria ... you can find them anywhere,"
said Walker, who was not part of the research team. "They are really
interesting."
Charles Knight, a cloud physics expert at the National Center for
Atmospheric Research in Boulder, Colorado, wasn't surprised by the
finding, however.
At relatively warm temperatures of just a few degrees below freezing,
bacteria are "remarkably effective" at attracting ice formation, said
Knight, who also was not part of the research group.
The study was supported by a Louisiana State University research
grant.
In a second paper published online by Science, researchers report
that the amount of dust blown into the tropical Pacific over the last
half-million years has varied widely between warm and cold periods.
Dust also has important impacts on weather and climate ranging from
serving as nuclei for rain to blocking some incoming radiation from the
Sun, and it also delivers minerals like iron that increase growth of
plankton in ocean areas.
Cores of seafloor sediment were taken from locations across the
tropical Pacific covering a period of 500,000 years.
Researchers led by Gisela Winckler of the Lamont-Doherty Earth
Observatory of Columbia University found that dust deposited in the
ocean peaked during cold periods and was less during warm periods. Using
isotopes, the scientists traced the dust on the western side to Asia and
that on the eastern side to South America.
They say the reasons for the change are complex(complicated), but in
general it tends to be windier in cold periods meaning more dust gets
blown around.
They found that cold peaks occurred about every 100,000 years, with
the last one at 20,000 years ago.
The research was supported by the National Science Foundation and the
Earth Institute at Columbia University.
- AP |