A UNLV-led research team used minerals preserved in ancient Nevada caves to offer the most concise climate history to date for the Great Basin region. The research, which includes samples dating back more than 175,000 years, was published May 2 in the online journal Nature Communications.
UNLV geoscientist Matthew Lachniet and collaborators from Cornell College and the University of New Mexico revealed that the climate of the Great Basin - which includes Nevada and parts of Utah, Oregon, Idaho and California - has followed the Earth's orbital variations like clockwork over the past 175,000 years, getting warmer and colder between conditions like today and during the ice ages.
Though the new research matches the theory of past climate change known to occur throughout the world, climate changes in the Great Basin has long been considered an anomaly and thought to be driven by different forces.
For more than 40 years, researchers believed that the timing of warming out of ice ages in the Great Basin occurred earlier than other regions, which was inconsistent with the changes to the Earth's orbit that drove climate change around the world.
"Our record is the first long-term and continuous record that shows unambiguously that the Great Basin climate was paced by the Earth's orbit around the sun," Lachniet said. "It also includes more samples over time than any other record."
Previous regional climate history came from Devil's Hole, Nevada, where scientists examined underwater formations. Lachniet and his team instead sampled stalagmites, or mineral deposits rising from a cave floor. Stalagmites grow in air-filled caves from dripping water and act as ancient rain gauges to help researchers form a more precise chronological record of climate history. Calcite minerals from tiny drops of water accumulate over thousands of years and, much like tree rings, accurately record the rainfall history of an area.
The samples were selected from cave deposits in Nevada in places such as Pinnacle Cave, Leviathan Cave and Lehman Cave in Great Basin National Park. The team collected a more comprehensive selection of samples than any other research done on this area to date.
"This stalagmite-based record, has precise absolute chronology, unlike the previous ice-core record. As a result we can establish the timing of these climate transitions with unprecedented certainty," University of New Mexico collaborator Asmerom said.
In addition, the new findings show that the growth of iconic pluvial lakes in the Great Basic were controlled by this regular pulsing of climate changes linked to the Earth's orbit. Pluvial lakes were huge lakes that covered a large portion of northern Nevada during the last ice age. The Great Salt Lake of Utah is a tiny remnant of past lakes of this era.
Based on the relationship of the variations in the Earth's orbit and Nevada's climate, Lachniet and his team suggest that the region won't see the re-appearance of pluvial lakes for another 55,000 years.
They also see evidence that the Great Basin climate has been warming for the past 1,600 years, which may signal the affects of humans on the climate.
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The study, "Orbital control of western North America atmospheric circulation and climate over two glacial cycles," was published in the online journal Nature Communications.
The climate history was constructed from cave deposits that were collected beginning in the 1990s in Nevada - areas included Pinnacle Cave on Mt. Potosi in Clark County; Leviathan Cave, north of Pahranagat Wildlife Refuge; and Lehman Caves in Great Basin National Park. The samples were collected with permits from the National Forest Service, Bureau of Land Management, and the National Park Service. The stalagmites were age-dated using Uranium series isotopes at the University of New Mexico, and the climate history put together using oxygen isotope analysis at UNLV's Las Vegas Isotope Science Laboratory.
Partnering with Lachniet were Rhawn Denniston of Cornell College, and Yemane Asmerom and Victor Polyak at the University of New Mexico. The project was recently funded by the Paleoclimate Program of the National Science Foundation.
