Scientists have known for a long time that variations in the Earth’s orbit dictate certain patterns in our climate, which is known as orbital forcing. In particular, these variations are largely responsible for oscillations of ice ages that have occurred over the last couple of million years. However, there was one anomaly that seemed to defy orbital forcing; the Great Basin climate.
Striking past climate data collected from Devils Hole in Nevada suggested that the climate of the Great Basin was out of sync with orbital variations and warmed out of glacial periods prior to temperature increases initiated by orbital changes. But a new study, published in Nature Communications, set the record straight on this matter and has demonstrated that ice age temperature oscillations in the Great Basin were indeed shaped by the Earth’s orbit.
In order to produce a reliable climate record for the area, researchers first precisely age-dated stalagmites using uranium series isotopes, and then obtained climate history data through oxygen isotope analysis. “This stalagmite-based record has precise absolute chronology, unlike the ice-core record that has to rely on compaction model derived relative ages,” said Professor Yemane Asmerom, one of the authors of the study. This revealed a 175,000 year climate record for the Great Basin.
The team found that, contrary to prior suggestion, Great Basin climate actually precisely followed variations in the Earth’s orbit during this period. In particular, they found that the data is in agreement with a theory first proposed by Serbian astronomer Milutin Milankovitch. The Milankovitch theory suggests that glacial cycles follow cyclical changes in the Earth’s orbit of the Sun. This is because variations in certain aspects of Earth’s orbit, such as axial tilt, affect the amount of solar radiation that can reach the Earth’s surface.
Despite divulging climate data on some of the same time intervals as Devils Hole, the researchers suggest that the latest record unequivocally demonstrates that the Great Basin was not an exception to Milankovitch forcing. “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,” said Matthew Lachniet, lead author of the study. “It also includes more samples over time than any other record.”
The team also found that these cycles dictated the growth of the pluvial lakes that once covered a large area in northern Nevada. The remaining Great Salt Lake in Utah is a merely a shadow of the great expanse of lakes that existed in the past.
The scientists also used the relationship between the climate in Nevada and the Earth’s orbital variation to predict that the pluvial lakes won’t replenish for another 55,000 years or so. They also suggest that over the past 1,600 years, the climate in the Great Basin has experienced warming that is not in line with the Earth’s orbits, inferring human influences may be at play.
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