By analyzing sediments up to 4,000 years old, Susan Zimmerman is hoping to provide a tool to help predict future climate change.

Ancient records of what was happening with climate conditions can be used with regional climate models to tell a story of what happened in the past and to correlate it to the present and the future.

Specifically, Zimmerman, who works as an environmental scientist at Lawrence Livermore National Laboratory's Center for Accelerator Mass Spectrometry (CAMS), along with colleagues Tom Guilderson and Tom Brown, are mapping patterns of past droughts in California by looking at lake sediments from the late Holocene period (0-4,000 years ago).

Through a Laboratory Directed Research and Development (LDRD) Program-funded project, the team will develop high-resolution, well-dated lake-sediment records of paleoclimate change in California, focusing on water variability. Predicting the timing, amount and patterns of precipitation using computer climate models that predict future patterns of change is especially critical in California, with its heavily engineered water distribution system.

Zimmerman is working with researchers across California to analyze lake sediments and develop records that span the last two millennia. These records will be used to map previous drought patterns in California and help climate modelers more accurately simulate the range of natural climate changes. With this information, state agencies can better determine the infrastructure needed to meet future demands for water.

Zimmerman's interest in lake sediments and their relationship to climate started when she was earning her Ph.D. at Columbia University, where she worked with geochemist Sidney Hemming at the Lamont-Doherty Earth Observatory. Outside of the LDRD project, she continues collaborating with Hemming to radiocarbon date sediments from Mono Lake, which borders the Eastern Sierras.

In sediments there from the last Ice Age (about 14,000-67,000 years ago), she found ostracodes, millimeter-scale crustaceans, that she plans to radiocarbon date at CAMS. Since shells from Mono Lake sediments can be difficult to radiocarbon date, Elena Steponaitis, an undergraduate student of Hemming's, will visit CAMS this month to perform an experimental leaching technique to try to measure the age of the shells more accurately.

"We want to determine what age they are and what they can tell us about the climate back then and what the lake was like," Zimmerman said. "We're very interested in the timing of the last big lake rise and subsequent drop at Mono Lake, and how those extremes fit into the warm/cold changes in Greenland and strong/weak monsoons in Asia at the end of the last Ice Age."

"Susan Zimmerman loads a sample of sediment in LLNL's large accelerator for mass spectrometry (AMS). The AMS uses isotopic ratios of carbon-14 to date the samples. (Credit: Photo by Jacqueline McBride/LLNL)"

Source: Lawrence Livermore National Laboratory