Underground gases tell story of ice ages.

• Position: Aquifers

Deep underground aquifers in the American Southwest contain gases that tell of the region's ancient climate, and support a growing consensus that the jet stream over North America at one time was split in two. The discoveries were made with a new paleohydrogeology tool--developed by geologists Chen Zhu of Indiana University, Bloomington, and Rolf Kipfer of the Swiss Federal Institute of Technology--that depends on the curious properties of noble gases as they seep through natural underground aquifers. Noble gases (neon and helium, for instance) are elements that resist chemical reactions and, therefore, have the potential to record information from Earth's past.

The tool's first serious test came amid the Navajo sandstone aquifers of northeast Arizona. "Getting to the point where we understand the interaction between these aquifers and the atmosphere above is going to open up many new ways to ask questions about the relationship between climate changes and water resources," explains Zhu.

"We have shown our approach can work extremely well. It confirms that the aquifer was recharged mostly during the Earth's most recent ice age, and particularly related to the fact that the jet stream was actually two jet streams many thousands of years ago, with the lower descending far to the south of North America."

An exhaustive and methodical sampling of groundwater from the Arizona sandstone aquifers shows significant changes in noble gas infusion rates and concentration...