September 28, 2012
Desert Climate In Western US Influenced By Ancient Water Cycle
Alan McStravick for redOrbit.com - Your Universe Online
The climate change we are currently experiencing, while disconcerting and increasingly uncomfortable, is not unprecedented when viewed through the historical prism of life on Earth.
A study led by researchers from Texas A&M University's Department of Oceanography looks back at the water cycle that affected the Western United States in an era dating back some 20,000 years. Focusing on the deserts of Utah and Nevada, the team is seeking to learn more about the large inland lakes that once covered this terrain and how those long-gone lakes still affect weather patterns across the region to this day.
Professor of oceanography Mitch Lyle, along with colleagues from Columbia University, University of California — Santa Cruz, Stanford University, Hokkaido University of Japan and Brown University, along with members of the U.S. Geological Survey, performed their research with funding from the National Science Foundation (NSF). Their results are published in the current issue of Science magazine.
In their study, the team worked with the long-held hypothesis that these large inland lakes were formed during the last glacial cooling period when large ice caps that covered what is modern-day Canada melted and released water that once covered as much as a quarter of both Nevada and Utah.
With new research, the team seeks to demonstrate a relationship between water cycles in the Southwestern region of the U.S. and the tropics. They believe that this connection, if demonstrated conclusively, will help researchers to understand how water cycles might be perturbed in the future.
Exploration of this region and the discovery of the dry shorelines of these glacial lakes dates back to nineteenth-century geological research, when the west was first being explored. At the time, the source of the additional water was unknown. It was only by poring over data related to the collection of ocean sediments, as well as samples culled from the dry western valleys, that Lyle and the team found a new water cycle connection linking the region to tropical influence.
"Large ice caps profoundly altered where storms went during glacial periods. Before this study, it was assumed that Pacific winter storms that now track into Washington and Canada were pushed south into central and southern California," Lyle notes. "However, by comparing timing between wet intervals on the coast, where these storms would first strike, with growth of the inland lakes, we found that they didn't match."
By examining pollen buried in marine sediments, Lyle was able to time wet periods along the California coast. These pollen samples were collected via core sampling performed by scientists associated with the Integrated Ocean Drilling Program at Texas A&M. Their lake level evaluations were drawn from southeast Oregon, Nevada, Utah, eastern California, New Mexico and west Texas, with the intent of determining when the lakes would fill in different parts of the west.
"Many teams of scientists have been working on this problem since the 1950s, when radiocarbon dating first allowed ages to be put on old shorelines," Lyle adds. "The data we synthesized covers a wide latitude so that we could determine how the glacial wet intervals operated."
Of particular interest was the observation that only in southern California´s coastal wet intervals was there a match to the high, inland lakes. This finding is what pointed the researchers to the tropical connection they had come to believe existed. This indicated that storms would cycle into the region from the tropical Pacific, originating west of Mexico.
"We think that the extra precipitation may have come in summer, enhancing the now weak summer monsoon in the desert southwest. But we need more information about what season the storms arrived to strengthen this speculation," Lyle says.
Not only is the development of the glacial lakes important for understanding prehistoric climate patterns, but Lyle believes it likely that the lakes were an important factor in the migration of people into North America. Many of the archaeological sites where early Indians settled when they first came into the U.S. are rock shelters at the edges of these ancient lakes. The lakes were a major source of fish and a gathering place for deer and wildfowl at that time.
"What we need to do now is look at all of this on a finer scale," Lyle points out. "We need to understand better the processes that directed the storms thousands of years ago, and to predict better what changes might occur in the future."