=START= XMT: 16:44 Wed Feb 06 EXP: 17:00 Sat Feb 09
ANCIENT ATMOSPHERIC LEVELS OF CARBON DIOXIDE MEASURABLE WITH NEW TECHNIQUE
WASHINGTON (FEB. 6) PR NEWSWIRE - A unique way to interpret data from sediments
from the ocean bottom may let scientists look back as far as 200 million years
at carbon dioxide in Earth's atmosphere. Previously the longest available
record of carbon dioxide, a major "greenhouse gas," was found in Antarctic ice
cores that show the last 170,000 years.
National Science Foundation-funded researchers at Indiana University -- John M.
Hayes, distinguished professor of biogeochemistry, and John P. Jasper,
postdoctoral research associate -- reported the new method in the international
In sediment core layers from a deep sea drilling site in the Gulf of Mexico,
Jasper and Hayes analyzed organic compounds from remains of algae that had
fallen to the sea floor during the past 100,000 years.
Like all green plants, the algae had used carbon dioxide -- dissolved in water
-- as the carbon source for building tissues by photosynthesis. When the algae
sank to the sea bottom and became part of the sediment, their records of
dissolved carbon dioxide were preserved.
Since there is a relationship between carbon dioxide dissolved in sea water and
carbon dioxide in the atmosphere, Jasper and Hayes were able to estimate
concentrations of carbon dioxide in ancient atmospheres.
"Until now, though it has been possible to estimate properties of ancient
climates from geological evidence, little has been known about the history of
atmospheric carbon dioxide," Hayes said. "As a result, it has been difficult
to refine understanding of greenhouse effects." Carbon dioxide is an important
factor in the greenhouse effect, in which Earth's temperature rises because of
trapped heat from sunlight.
The new method of analyzing sea sediments relies on measuring the proportion of
carbon-13 to carbon-12 in organic materials. Carbon-13 is a heavier but stable
isotope of carbon with a nucleus containing seven neutrons and six protons.
The more common carbon-12 has six of each.
Based on observations by plant biologists, Hayes and Brian Popp (now on the
faculty of the University of Hawaii) had earlier reasoned that the proportion
of carbon-13 to carbon-12 in the algae would be related to carbon dioxide
levels in the atmosphere. Hayes and Jasper then searched in the sea sediment
cores for this "isotopic signal."
"We were able to show that an isotopic signal related to atmospheric carbon
dioxide levels can be seen," Hayes said. "It was a good quantitative
relationship allowing calibration of this 'paleobarometer.'"
The researchers focused on the past 100,000 years because they could compare
results with the findings of scientists who had directly measured the amount of
carbon dioxide trapped in different layers of Antarctic ice when the layers
were formed during the same 100,000 years. Results matched, indicating that the
new technique will work at least for the last few hundred thousand years (the
age of Antarctic ice).
Hayes noted that the relationship between carbon dioxide might depend on algal
biochemistry. The algae examined by Jasper and Hayes evolved less than a
million years ago, so it is possible that the calibration based on the Gulf of
Mexico core will be usable only for that time interval. Further work will be
needed to determine that.
CONTACT: Cheryl Dybas of the National Science Foundation, 202-357-9498