Climate history captured in caves

[one...two...tree 2,762]

Seth Shulman, Grist

Julia Cole finds evidence of the climate record in some fascinating places. Cole is a geologist at the University of Arizona. Most recently, her research has led her deep inside a limestone cave 50 miles southeast of Tucson. Preserved there, within stalagmites that have formed on the floor of the dark, perpetually humid cave, is what Cole calls "a robust archive" of climate history in the desert southwest.

The stalagmites contain an almost continuous climate record that dates back tens of thousands of years to the last ice age, a time when ice sheets covered much of North America. Subtle changes in the composition of a stalagmite as it forms, says Cole, "establish a record that ties into large-scale climate patterns."

We know about these broad climate changes from many sources, Cole explains. But "no one had documented those changes before in such revealing detail over a long period of time in the Southwest of the United States."

The key to Cole's technique is her understanding of how stalagmites form. As rainwater percolates down through the soil above a cave, it loses carbon dioxide. As the water drips onto the cave floor it leaves behind mineral formations of calcium carbonate. These lumps of calcium carbonate, Cole explains, contain "preserved records of precipitated rain soaked through a filtering process."

Cole unlocks the stalagmites' secrets by capitalizing on the fact that their chemical composition differs subtly between wet and dry periods. In dry years, stalagmites contain more oxygen-18. This rare, heavier isotope of oxygen is less likely to evaporate in a dry period than the lighter and vastly more common form of oxygen.

By shaving the stalagmite's core into 100-micron-thin layers, measuring small changes in the abundance of oxygen-18, and applying a sophisticated dating technique, Cole's team can reconstruct when the region was wet and when it was dry.

Cole's approach is similar to that taken by scientists who chart climate variability by studying tree rings. But, says Cole, "tree ring data has limitations. Trees don't live that long. And, even more importantly for this region, there are no trees in the desert, only in the surrounding mountains." Now, she continues, "we have a solid set of paleoclimate data below the tree line."

http://www.grist.org...mate-scientist/

[PhiLandShiR 18]

I read about this a few years back. Pretty interesting research being done. Using tree rings worked well in Europe because of more trees there. I think the climate has been recorded in tree rings for 7 or 8 thousand years for Europe , but I could be wrong....

[Nagishkaw 510]

This is interesting. Thanks for the post!