Geologists have long thought the loess -- or fine silt -- that accumulated on the Chinese Loess Plateau was carried on winds from desert regions to the northwest over the past 2.6 million years. New research indicates the loess may actually have come from due west, which would change conventional thinking about wind patterns during that period.
A team of geologists from the U.S. and China -- led by the University of Rochester -- compared the composition of uranium and lead in zircon crystals excavated from the Chinese Loess Plateau and potential source sites. The scientists found that the ages of the crystals from the Chinese Loess Plateau matched with samples from the northern Tibetan Plateau and the Qaidam Basin, both of which are due west.
The results have been published in a recent issue of the journal Geology.
"The data suggest a dramatic shift in atmospheric winds," said lead author Alex Pullen.
By testing for the ages of the embedded zircon crystals, the researchers determined that the loess came from the west during recent glacial periods, which suggests that the atmospheric jet streams shifted equatorward during those periods. That would mean there have been alternating northwesterly and westerly sources for the loess during warm interglacial and cold glacial periods, respectively. The geological team says additional studies of ancient soil (paleosol) layers of the Chinese Loess Plateau are needed to test that theory.
"The research should help us better understand how the Earth behaves as a system," said Pullen. "With that knowledge, we'll be able to improve our climate models."
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