In a "proof of concept" study of the oxygen isotopes found in the cellulose of late-season growth in annual growth rings from pine trees near Valdosta, Georgia, a team led by Claudia Mora found they could identify all known hurricanes that hit the area over the past fifty years.
But that's just the beginning, says Mora, who is scheduled to present some of her team's findings on Thursday, 11 August, at Earth System Processes 2, a meeting co-convened by the Geological Society of America and Geological Association of Canada this week in Calgary, Alberta, Canada. "We've taken it back 100 years and didn't miss a storm," said Mora.
Since a century is a very short time when it comes to climate change, she and her team applied their new technique to old trees from other parts of the Southeastern US and found a tropical cyclone record spanning 227 years. They've even found additional climate information going back as far as 1450 AD.
"What we're trying to do is understand frequency of hurricanes and how variable their occurrence is over the long-term," said Mora. "We're trying to come up with a reliable way to establish this."
Mora's group divided each individual annual tree ring in the trees into early-year and late-year growth. That way they could isolate the late-year hurricane season. Then they searched all the woody tissues for any sudden drops in a particular oxygen isotope: oxygen-18. That is the hurricane signal, Mora said.
What makes drops in oxygen-18 so telling is that it matches up with a little known talent of all hurricanes: they are very good at depleting the air of oxygen-18, Mora says.
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Contact: Ann Cairns
acairns@geosociety.org
303-357-1056
Geological Society of America
10-Aug-2005