Sunday, February 5, 2012

UNLV Researcher Finds Stalagmites May Reveal Clues to Climate Change by Henry Brean

Matthew Lachniet, an associate professor at UNLV, looks at rock formations in a cave in the Sierra Madre region of Mexico during a June 2011 trip. Lachniet says cave rock accurately records rainfall patterns through the centuries. His research might help explain the rise and fall of Mesoamerican civilizations.

Across the sweep of a thousand years, as ancient cities bloomed and died in southern Mexico, the water in Juxtlahuaca Cave went drip, drip, drip.

Now a UNLV researcher is using a stalagmite built by those droplets to chart 2,500 years of rainfall and draw new links between human history and climate change.

The findings by professor Matthew Lachniet and his research team could help shed light on Nevada's climate over the past several thousand years and offer clues to how it might change in decades to come.

"We have a saying in geo­science: The past is the key to the future," said Lachniet, a geologist and climate scientist at the University of Nevada, Las Vegas.

Scientists have only recently begun to unlock the secrets of cave formations as "ancient rain gauges," he said.

Outside of tree rings, stalagmites offer one of the most accurate climate records known to science because they tend to grow at a uniform rate and collect traces of naturally occurring uranium.

And since they are formed by minerals in water droplets that crystallize and accumulate over the course of thousands of years, stalagmites can offer a much longer record than tree rings.

Lachniet and company were able to pinpoint the age of various layers in the stalagmite from Juxtlahuaca to within about 10 years. They could then track rainfall amounts over time by analyzing carbon dioxide trapped in those layers.

What researchers discovered was a period of above average rainfall between the first and third centuries that coincided with the rise of the largest early Mesoamerican city of Teotihuacan, near present day Mexico City.

That was followed by a 500-year drying trend and more than a century of drought, during which came the rapid collapse of the city around 550 A.D.

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