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Ancient Redwoods Of The Far North

a time of plenty for mammals
Baltimore - Mar 21, 2002
Once upon a time, Axel Heilberg Island was a very strange place. Located within the Arctic Circle north of mainland Canada, a full 8/9ths of the way from the equator to the North Pole, the uninhabited Canadian island is far enough north to make Iceland look like a great spot for a winter getaway, and today there's not much to it beyond miles of rocks, ice, a few mosses, and many fossils.

The fossils tell of a different era, though, an odd time about 45 million years ago when Axel Heilberg, still as close to the North Pole as it is now, was covered in a forest of redwood-like trees known as metasequoias.

Hope Jahren, an assistant professor of earth and planetary sciences in the Krieger School of Arts and Sciences at The Johns Hopkins University, recently published results that partially demystified Axel Heilberg's vanished forests. Jahren and colleague Leo Sternberg of the University of Miami uncovered evidence that the Axel Heilberg's forests probably received equatorial water and warmth from a prehistoric weather pattern unlike anything in existence today.

Other challenging mysteries remain, including how a forest could develop given the sunlight it would receive on Axel Heilberg. Because of its closeness to the North Pole both now and in the time of the redwoods, Axel Heilberg spends four months of each year in continuous sunlight and four months of each year in continuous darkness.

"We don't have plants that can survive under those conditions today, let alone forests," Jahren says. "For a tree to endure four months of daylight is like you or I going without sleep for four months."

Through a grant from the Andrew Mellon Foundation, Jahren's research group has made three summer visits to Axel Heilberg, excavating hundreds of fossil metasequoias. The fossils are immaculately well-preserved.

"Some of this stuff looks about like driftwood on the beach, but it's 45 million years old," Jahren says. "These fossils are chemically preserved at a level you usually would expect to see in something that's only 1,000 years old."

That's ideal for Jahren, who studies the presence of isotopes of elements like carbon, nitrogen and oxygen in living and fossilized plants. Isotopes are forms of an element that differ only by the addition of one or more subatomic particles known as neutrons. Different isotopes of the same element have different mass, which affects the way plants use them.

Jarhen, the winner of last year's Geological Society of America Donath Medal for most promising young scientist, studies the isotopes to learn more about plants' relationship to weather and climate change. In her group's first major Axel Heilberg results, published in the January issue of the Geological Society's "GSA Today," they measured the presence of isotopes of oxygen and hydrogen in the fossilized metasequoias.

"The wood of any tree growing anywhere records fairly faithfully the oxygen and hydrogen chemistry of the water the plant has access to through precipitation," Jahren explains. "And there's a great deal of difference between the chemistry of water that arrives at a certain location after being transported [in evaporated form] great distances over land versus the chemistry of water that arrives at a place after being transported over water or not being transported very far."

Jahren and co-author Sternberg chemically compared the fossil isotope levels with those found in water in contemporary precipitation patterns over great distances of forested lands in the Amazon. They were able to show that water traveling from near the equator almost due north across the continents to the vicinity of Axel Heilberg would have oxygen and hydrogen isotope signatures that matched those found in the fossils.

While it might seem mind-boggling to have the equator watering the north pole, Jahren notes that other major climatological differences at the time included the lack of a north polar ice cap.

"It's very hard to explain the isotope chemistry of the precipitation using any other model of water transport," Jahren says. "So we think we've basically solved a piece of the puzzle."

As for the other major piece of the puzzle -- survival of the trees through extended periods of light and dark -- Jahren's group is working to see if the isotope chemistry of the fossils can help them learn how the metasequoias' metabolism compared to those of contemporary plants.

"Did they function similarly to how plants function now?" Jahren asks. "Or did they have strategies that plants either no longer have or no longer employ? Were they fundamentally different? These fossils are really forcing us to expand our ideas of how ecosystems can work." Related Links
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Are Northern Forests a Byproduct of Acid Rain
Corvallis - Mar 18, 2002
Studies of pristine forests in South America found that the cycling of nitrogen, an essential nutrient, was quite different than expected, and it suggests that many forests of North America and Europe actually have an unnatural ecology driven largely by air pollution, acid rain and artificial nitrogen fertilization.


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