FW: coral reef news

Paterson, Arthur apaterson at ocean.nos.noaa.gov
Sat Apr 3 07:50:57 EST 1999

Institution: National Center For Atmospheric Research (NCAR)
Contact: Anatta , Media Relations
E-mail: anatta at ucar.edu, Phone: 303-497-8604
Posted 04/1/99 Increasing Carbon Dioxide Threatens Tropical Coral Reefs

BOULDER--Tropical coral reefs could be directly threatened by the buildup
of atmospheric carbon dioxide (CO2) entering the oceans, and some reefs
may already be declining, say six scientists in a paper published in the
April 2 issue of the journal Science. Writes lead author Joan Kleypas of
the National Center for Atmospheric Research (NCAR), "We believe that
these findings represent some of the first evidence of a direct negative
impact of increased CO2 on a marine ecosystem."  NCAR's primary sponsor is
the National Science Foundation.

The team's findings apply primarily to coral reefs located in surface
waters between 35 degrees north and 35 degrees south of the equator.
However, the authors predict that reefs in greatest danger are those where
the production and destruction of calcium carbonate are closely balanced.
These include some higher-latitude reefs, such as those off Bermuda; those
in areas where colder, deeper waters rise to the surface, such as those
off the Galapagos Islands; and many reefs already stressed by human

A coral reef is the accumulation of calcium carbonate produced by the
corals and other calcium-secreting organisms, such as coralline algae. If
calcium production declines, coral and algal skeletons will weaken and
reef building may slow or stop. The reef then becomes more vulnerable to
erosion. Ongoing calcium production depends on the saturation state of
calcium carbonate in surrounding surface waters. This saturation state
declines as CO2 enters tropical surface waters.

Carbon dioxide is an important greenhouse gas produced by fossil-fuel use.
For their study, the authors used future scenarios in which the
preindustrial level of CO2 doubles by the year 2065--considered a moderate
projection by the Intergovernmental Panel on Climate Change, an
international group of 2,500 scientists. As the gas builds up in the
atmosphere, the tropical sea surface takes it up at a proportional rate.
Scientists have so far focused on CO2 storage in the ocean. This is one of
the first studies to examine how CO2 increases may affect the chemistry
and biology of ocean ecosystems.

As CO2 dissolves, it produces an acid that lowers the seawater pH. The
interaction of carbon dioxide with calcium carbonate in seawater decreases
the level of calcium carbonate saturation.  Given the rapid rise in CO2
levels expected over the coming decades, the authors project that by the
year 2065, the interaction of CO2 with seawater will have reduced calcium
carbonate saturation in tropical surface waters by 30% relative to
preindustrial levels.

The findings are based on ocean carbon data and computer models, and on
laboratory experiments which show that coral and algal calcification
declines as the saturation state declines. The coral reefs themselves have
not been studied in situ. "Our work is somewhat speculative," says
Kleypas. "We need more studies at the ecosystem level. If the laboratory
results bear out in the oceans, I think many species of coral reefs could
be vulnerable."

The buildup of CO2 may also warm ocean surface temperatures. Although
warmer sea-surface temperatures are being blamed for the recent increase
in coral bleachings worldwide, some feel that this warming could be a boon
for reefs in chilly waters. However, says Kleypas, if the calcium
carbonate saturation rate is as important as water temperature in reef
building, warmer waters won't save higher-latitude reefs.

NCAR is managed by the University Corporation for Atmospheric Research, a
consortium of more than 60 universities offering Ph.D.s in the atmospheric
and related sciences.

                      -The End-

UCAR and NCAR news: http://www.ucar.edu/publications/newsreleases/1999

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