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Decoding Diatoms Sediment records of past algal communities inform today’s climate change investigations by Margaret Nagle

Jasmine Saros

Every summer for the past decade, paleoecologist Jasmine Saros has trekked across snowfields and horsebacked up bouldered mountain passes to reach remote, high-altitude lakes in the shadow of the Beartooth Mountains of the central Rockies. In the pristine wilderness of Montana and Wyoming, at altitudes above 9,400 feet, she arrives at the alpine lakes just after ice off to study changes in the algal community, looking for evidence of climate change and airborne pollution.

Saros, an associate professor in the University of Maine Climate Change Institute and School of Biology and Ecology, is focusing on diatoms living in the water column and preserved in the lake sediment, the remains of their silica cell walls testifying to their centuries of existence. By combining ecological field observations and bioassays with paleolimnology, Saros studies the diatom fossil records to reconstruct environmental change and to better understand the mechanisms driving the change, past and present.

Diatoms, one of the most common groups of phytoplankton, are part of the base of the food web, where changes in such fundamental species can cause ripple effects. In Saros’ research, diatoms are tools for understanding what’s happening chemically and physically in lake ecosystems.

Sediment cores reveal that in the past 10,000 years, the abundance of various Cyclotella, one of the most common diatom groups, has fluctuated in lakes in the central and northern Rockies. However, in the 20th century, the diatoms’ numbers have increased not only in the Rockies, but also worldwide in alpine and temperate lakes, as well as in the Arctic.

“Many people believe that’s a sign of global warming,” says Saros. “What we don’t know is the mechanism driving the increases, and whether it is the same catalyst across all lakes.”

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Fall 2009

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