Baylor Study Finds El Nino, La Nina Happened in Eastern U.S. Earlier Than Previously ThoughtJuly 27, 2009
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A Baylor University study has found the weather patterns of El Niño and La Niña, which brings drier and wetter conditions to certain parts of the country, happened thousands of years earlier than previously thought.
Scientists believe El Niño and La Niña started during the Late Tertiary period, 65 million to 1.8 million years ago, however, exactly when during that time is not yet known until now.
"The conventional wisdom was that these weather patterns started during or after the Isthmus of Panama closed about three million years ago and water stopped being exchanged between the Pacific Ocean and the Atlantic," said Dr. Steven Driese, chair and professor of geology at Baylor who oversaw the research project. "This study shows it happened well before that."
The study appeared in the July volume of The Journal of Paleolimnology.
The Late Tertiary period is a crucial period in earth history because it represented warm weather conditions immediately prior to the development of extensive northern hemisphere glaciers. It is widely believed this period provides the best available analog for predicting climate changes associated with global warming that the world is presently experiencing.
There is little preservation of deposits of the Late Tertiary age preserved in the eastern half of the United States and subsequently very little is known about the climate conditions of this region during that time. However, the recently discovered Gray Fossil Site in northeastern Tennessee includes a sinkhole lake filled with well-preserved sedimentation and fossils that acts as a good record of the Late Tertiary period from four million to seven million years ago.
At the Gray Fossil Site, Baylor researchers examined the thickness of the sediment layers by placing pins to mark the positions of each distinct layer in the sediments and then measured the spacing of the layers. This allowed them to generate a set of sequential layer-thickness measurements that could be solved mathematically. Using a time-series analysis, they determined there were patterns of recurring thicknesses, with repetitions that were four and 24 years apart.
"The 24-year repetition corresponded to Hale sunspot cycles, which can influence weather conditions," Driese said. "The only known mechanism for the three-to-four year cycles is El Niño and La Niña variations in climate."
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