Collaborative Research: Testing the hypothesis of an orbital forcing of southwestern North America climate over the past 500,000 years

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Climate scientists have long documented the strong control of Earth's orbital variations on the waxing and waning of the ice ages. Thirty years ago, an iconic climate record from Devils Hole, Nevada, seemed to suggest that Great Basin the climate of the Great Basin of the western United States was out of step with the orbital rhythm, warming after glacial periods before what would be expected from changes in the Earth's orbit. Now new evidence places Great Basin climate variations back in synchrony with orbital variations, and shows that climate warmed and cooled with the amount of solar radiation reaching the northern Hemisphere during summer over the last 175,000 years. Radiometrically-dated stalagmites from Great Basin caves have the potential extend the record back to 500,000 years before present. These cave deposits record variations in climate in a broad region over and upwind of the cave sites. As such, they are ideally suited to test for an orbital control on Great Basin climate, and will allow comparison to sea surface temperature records in the Pacific Ocean, and to the Devils Hole calcite record. This project will also facilitate long-term climate projections for the southwestern United States based on known future orbital variations. The overarching hypothesis that will be tested in the course of this project is that southwestern paleoclimatic change was paced by Milankovitch (orbital) forcing, through changes in northern hemisphere summer insolation altering atmospheric circulation dynamics over the northeastern Pacific Ocean region. The research team will generate high-resolution oxygen isotope analyses of precisely-dated stalagmites from caves across the Great Basin region, and determine whether or not oxygen isotope variations align with variations in northern hemisphere summer insolation over the past half million years. Oxygen isotopic analyses will be carried out at the University of Nevada Las Vegas, and uranium disequilibrium dating at the University of New Mexico. The research team will include several students from both lead institutions as well as an undergraduate-serving institution, Cornell College (Iowa). The researchers and students will also create cave educational materials for sharing with local caving groups and governmental agencies.