The Log | School News
Droughts Like the Great Dust Bowl of the 1930s
May Have Been Unexceptional in Prehistoric Times, New Study
Suggests
Events like the great Dust Bowl
of the 1930s, immortalized in The Grapes of Wrath and remembered
as a transforming event for millions of Americans, were regular
parts of much-earlier cycles of droughts followed by recoveries
in the region, according to new studies by a multiinstitutional
research team led by Duke University.
Some of those prehistoric droughts
in the northern Great Plains of what is now the United States
also lasted longer than modern-day dry spells such as the
1930’s Dust Bowl decade, according to sediment core studies
by the team.
The group’s evidence implies these
ancient droughts persisted for up to several decades each.
At their heights, prairie fires became uncommon because there
was too little vegetation left to burn. The ages of charcoal
deposits suggest instead that prairie fires occurred during
intervening wet periods, with each wet-dry cycle lasting more
than a century.
A report on the research was delivered
during the Ecological Society of America’s 2004 annual meeting
in Portland, Ore.
“We were looking for the effects
of past climate changes on ecosystems,” said James Clark,
H.L. Blomquist Professor of Biology at the Nicholas School.
But when Clark and his colleagues began examining evidence
from the mid-Holocene period of 5,000 to 8,000 years ago in
parts of the Dakotas, Montana and western Minnesota, “nothing
seemed to make any sense.”
“The question was: Could we look
at the sediments for charcoal evidence of the amount of fire,
for pollen evidence of the kinds of grasses that were growing
then, for sediment chemistry to show how much erosion was
going on, and be able to deduce climate changes—or the lack
of them—under way at the time?” Clark said.
When he and his colleagues finally
determined the correct intervals between samplings was about
once every decade, “The patterns just jumped right out at
us,” he recalled in an interview. “We were seeing these very
coherent drought cycles.”
To make these deductions, Duke post-doctoral
investigator Kendrick Brown evaluated prehistoric charcoal
deposits. Joe Donovan, a geophysicist at the University of
West Virginia, studied the geochemistry of the soil samples.
Eric Grimm and Pietra Mueller of the Illinois State Museum
in Springfield investigated pollen in the sediments. For the
complete story go to www.dukenews.duke.
edu/news/dustbowl_0804.html.
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