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A Geological Dating Game: Lichens Help Track Recent Climate Change

Date: Aug. 22, 2001
By: Chris Curran
Photos by Colleen Kelley
Contact: Dawn Fuller
Phone: (513) 556-1823
Archive: Research News

There is little question that many of the Earth's great glaciers have been retreating since the Little Ice Age reached its most recent advanced position in the mid 1800s.

However, traditional geological dating methods aren't always useful in tracking such recent climate changes. View from Alaska

Radiocarbon dating doesn't always work, and neither does a technique called denodrochronology which relies on counting tree rings. There aren't always trees to measure, which quickly rules out using that technique.

It turns out tiny, but durable little lichens might serve as a useful biological calendar for the time period up to 300-500 years ago. To geologists, that would be 300-500 B.P. (before present).

Katie Schoenenberger, a recent UC master's graduate (June 2001) is helping to refine the technique of lichenometry for dating glacial retreats in the Northern and Southern Hemispheres. Lichens are hardy combinations of fungi and algae which can grow on rocks and live for hundreds of years. Katie Schoenenberger in Alaska

Schoenenberger has sampled lichen populations in New Zealand, Iceland and the Canadian Rockies over the last two years. This August, she's planning to sample four different glaciers in south central Alaska (Portage Glacier, Kennicott Glacier and two in the Alaska Range).

"The idea is to sample the whole population to reduce error," explained Schoenenberger. The previous lichenometry technique focused solely on the largest lichen in a particular area.

The assumption was that the largest lichen was the first to colonize an area after a glacier retreated, but scientists quickly realized the potential for errors. A single sample is rarely good enough for a solid scientific study.

Katie began her studies in New Zealand, sampling areas where there were already solid dates for glacial retreats using other methods. She's now trying to develop calibration curves for glacial systems in the Northern Hemisphere.

It's difficult work, because the target species, Rhizocarpon geographicum, grows at different rates depending on where you find it. It has a constant growth rate, which is useful for dating purposes, but that rate will vary depending on factors such as altitude, wind, and competition from other vegetation.

"I don't think we're close to calibration curves for the Northern Hemisphere," she admits.

What she hopes to accomplish this year is to get a good handle on the variability associated with lichenometry sampling.

"Once we get some measures of variability, it will be easier to analyze the data."

Schoenenberger will continue her work in collaboration with UC geology professor Thomas Lowell who led the trip to Alaska as part of a course on glaciers and global climate change.

Click here for more on the adventures of another UC geologist.

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