New material forms on the otolith in a series of growth rings much like those found in trees. When the water is cool, the material accumulates relatively more of the heavier oxygen-18 isotope. By analyzing samples of calcium carbonate taken from individual otolith rings, the researchers can, among other things, recover seasonal temperature records for periods of time where none now exist.
It was Ivany's idea to use this technique to study seasonal variations across the Eocene/Oligocene boundary during which the extinctions occurred. "While scientists often develop methods of resolving Earth history at time scales of days to weeks or months, it takes the insight of researchers like Dr. Ivany to apply existing analytical techniques to questions that address global scale problems," says Lohmann.
In fact, "this is the first time anyone has looked at seasonality as a variable for an extinction event across a geological time boundary," Patterson adds. "We proved that winter temperatures caused the extinction. Existing records weren't able to resolve the change because the records are based on summertime growth. The fish survived the drop in winter temperatures and left a permanent record, while the mollusks didn't make it to the other side of the boundary."
Ivany plans to continue her work on Eocene and Oligocene climate and how it relates to extinction events. She will e
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Contact: Nancy Ross-Flanigan
rossflan@umich.edu
734-647-1853
University of Michigan
17-Oct-2000