IU INVOLVED IN RESEARCH PROVING CLIMATE CHANGE IN SOUTHERN CALIFORNIA RECORDED BY SEDIMENTS IN SODA LAKE

BLOOMINGTON, Ind. -- The chemistry of organic matter in sediments from Soda Lake in southern California suggests that the climate there was wetter with more woody vegetation as recently as 370 years ago (about 10 years after the Pilgrims landed at Plymouth Rock in what is now Massachusetts).

Soda Lake, about 40 miles east of San Luis Obispo, provides a valuable window into recent climate change because it is in a basin that has been minimally disrupted by industry and agriculture. Scientists from Indiana University, Arizona State University, Whittier College and Dickinson College are collaborating in an effort to unravel the records of climate change and seismic activity in this basin, which is close to the high population centers of southern California. They will present their first results at the annual meeting of the Geological Society of America in Salt Lake City, Utah, on Tuesday (Oct. 21).

"Sediment records from Soda Lake indicate a significant perturbation of long-term climate that occurred around 370 years ago," said Lisa Pratt, professor of geological sciences and Gill Fellow in geological sciences at Indiana University.

"Although we are not yet able to correlate the Soda Lake climate record with oceanic records of past El Nino and other climate phenomena, this is the type of terrestrial evidence that scientists seek in order to reconstruct the timing and magnitude of recent climate change," Pratt added.

Little rainfall, low levels of plant and animal life in the lake, and a shortage of dissolved oxygen in the water at the bottom of the lake combine to make Soda Lake an ideal place to investigate climate evidence preserved in the organic matter of sediments that were washed into the lake hundreds of years ago.

This salt lake occasionally dries up in late summer. The Soda Lake Basin is surrounded by mountains which cut it off from outside water sources, and the basin is bordered on the east by the San Andreas Fault. Recent lake expansions and contractions are indicated on the basin floor by broad mud-cracked areas that were once lake bottom. The lack of evidence for previous higher lake levels on the surrounding valley walls suggests that Soda Lake has never had a substantial depth of water. Drainage of water from the surrounding land surface into the lake is now minimal, and groundwater entering the lake below its surface appears to maintain the lake's water level, replacing water lost by evaporation.

To evaluate the climate record of this basin, the scientists collected a sediment core from the lake to a depth of 65 centimeters. They determined the amount of organic carbon and the proportion of carbon-13 to carbon-12 in this organic matter at various depths in the core. They found that the amount of organic carbon in salt-free sediments drops rapidly in the top 10 centimeters of the core to a value that then remains relatively constant through the remainder of the core.

However, at a depth of 40 centimeters, they noticed a pronounced increase in organic carbon content and a significant change in the proportion of carbon-13 to carbon-12 in a sediment layer containing woody fragments, which were dated by carbon-14 methods to 370 years ago. This age coincides with what scientists have widely recognized as an intervalof wetter climate and flooding in the region.

The scientists concluded that Soda Lake sediments appear to preserve a highly detailed record of climate change in southern California.

For more information, contact Hal Kibbey, Office of Communications and Marketing, 812-855-0074 or 812-855-3911, hkibbey@indiana.edu

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