Stalagmite Provides Clues to Drought-Solar Influence
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.
"This really nails down the idea of solar influence on continental drought," said Springer, an assistant professor of geological sciences.
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.
In the recent study, the scientists cut and polished the stalagmite, examined the growth layers and then used a drill to take 200 samples along the growth axis. They weighed and analyzed the metals and isotopes to determine their concentrations over time.
Though modern records show that a cooling North Atlantic Ocean actually increases moisture and precipitation, the historic climate events were different, Springer said. In the past, the tropical regions of the Atlantic Ocean also grew colder, creating a drier climate and prompting the series of droughts, he explained.
The climate record suggests that North America could face a major drought event again in 500 to 1,000 years, though Springer said that manmade global warming could offset the cycle.
"Global warming will leave things like this in the dust. The natural oscillations here are nothing like what we would expect to see with global warming," he said.