The findings, just published in the journal Nature Communications, provide new insight into the region's hydroclimate and how it may evolve in the future, said Kathleen Wendt, an assistant research professor at Oregon State University and the study's lead author.
"What we see over this time span are glacial periods, when Nevada was cooler and wetter, followed by interglacial periods, when Nevada was hot and dry, like what we're experiencing today," Wendt said.
"But midway through those interglacial periods, the available groundwater dropped sharply and vegetation plummeted."
Wendt is a paleoclimatologist who studies deposits of the mineral calcite, which build up in caves over thousands of years, creating a record of Earth's climate history.
"While scientists have long used cores of ancient ice collected in Antarctica and Greenland to study climate history, it is difficult to find terrestrial, or land-based, environmental archives that record past climate, especially in places that are dry and arid, like the southwest United States," Wendt said. "Caves are one place we can look for these records."
Past research identified the Devils Hole cave system in southwestern Nevada as a likely source for climate records. Devils Hole is more of a fissure than a traditional cave. Groundwater has been flowing through the fissure for hundreds of thousands of years and depositing calcite on the walls of the fissure, much like how hard water deposits inside the pipes of a home, Wendt said.
For her study, Wendt and colleagues descended 20 meters down a narrow shaft and squeezed through a tight opening to reach the deepest part of Devils Hole II. Once there, they drilled a one-meter-long core of calcite from the cave wall. The oxygen isotopes within the calcite vary based on climate conditions at a given time, allowing scientists to reconstruct the region's climate history.
"This meter-long core gives you a record of how climate has changed over half a million years," Wendt said. "There aren't a lot of caves like this in the world."
Analysis of the core showed how the region's hydroclimate changed during the last six ice ages, or global periods of colder temperatures and the interglacials, or warmer periods, that interspersed between them.
Researchers also learned about when and where rain fell and how that changed over time, said Christo Buizert, an associate professor in OSU's College of Earth, Ocean, and Atmospheric Sciences and co-author of the study.
"Today, the bulk of the rainstorms coming off the ocean hit the Pacific Northwest, but during ice age periods, that same belt of rainstorms would land a lot further south," Buizert said. "That tells us these storm systems can move up and down the coast, and they can shift quickly and dramatically."
If that rainfall occurs in the winter, it recharges the local aquifer. These changes in the availability of groundwater impact vegetation productivity; when temperatures were hot and groundwater availability was reduced, vegetation also declined, the researchers found.
The records from the calcite deposit provide a sense of timing for those vegetation changes in relation to climate change and suggest that temperature, availability of water and vegetation are tightly coupled, with changes in one area impacting the others, Buizert said.
"This raises questions about what we might expect in this region in the future as climate continues to change," he said. "This part of the world is already on the cusp of livability with high summer temperatures and limited water resources."
Additional co-authors on the paper are Stacy Carolin of the University of Oxford; Simon Steidle; Gina Moseley, Yuri Dublyansky and Christoph Spotl of the University of Innsbruck; R. Lawrence Edwards and Mellissa Warner of the University of Minnesota; and Hai Cheng of the Chinese Academy of Sciences; and Chengfei He of the University of Miami.
Wendt, who worked on the project while with the College of Earth, Ocean, and Atmospheric Sciences at Oregon State University, recently accepted a new role at the University of Toronto.
Research Report:Controls on the southwest USA hydroclimate over the last six glacial-interglacial cycles
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