Ohio University: Global Warming
New Climate Record Shows Century Long Droughts in Eastern North America - 08/19/08
A stalagmite in a West Virginia cave has yielded the most detailed geological record to date on climate cycles in eastern North America over the past 7,000 years. The new study confirms that during periods when Earth received less solar radiation, the Atlantic Ocean cooled, icebergs increased and precipitation fell, creating a series of century-long droughts.
A research team led by Ohio University geologist Gregory Springer examined the trace metal strontium and carbon and oxygen isotopes in the stalagmite, which preserved climate conditions averaged over periods as brief as a few years. The scientists found evidence of at least seven major drought periods during the Holocene era, according to an article published online in the journal Geophysical Research Letters.
Geologist Gerald Bond suggested that every 1,500 years, weak solar activity caused by fluctuations in the sun's magnetic fields cools the North Atlantic Ocean and creates more icebergs and ice rafting, or the movement of sediment to ocean floors. Other scientists have sought more evidence of these so-called "Bond events" and have studied their possible impact on droughts and precipitation. But studies to date have been hampered by incomplete, less detailed records, Springer said.
The stalagmites from the Buckeye Creek Cave provide an excellent record of climate cycles, he said, because West Virginia is affected by the jet streams and moisture from the Gulf of Mexico and the Pacific Ocean.
Other studies have gleaned climate cycle data from lakes, but fish and other critters tend to churn the sediment, muddying the geological record there, said study co-author Harold Rowe, an assistant professor of geological sciences at the University of Texas at Arlington.
Strontium occurs naturally in the soil, and rain washes the element through the limestone. During dry periods, it is concentrated in stalagmites, making them good markers of drought, Rowe explained. Carbon isotopes also record drought, Springer added, because drier soils slow biological activity. This causes the soil to "breathe less, changing the mix of light and heavy carbon atoms in it," he said.
