Coral Reefs Unlikely To Survive In Acid Oceans
Pastor Dale Morgan
Coral Reefs Unlikely To Survive In Acid Oceans*
In year 1750, over 98 percent of coral reefs (magenta dots) grew in
optimal conditions with aragonite saturation greater than 3.5 (blue
colors). Such water is rapidly disappearing and will be gone in several
decades if current carbon dioxide emission trends continue. Atmospheric
CO2 levels are 280 ppm and 550 ppm for years 1750 and 2050,
respectively. Credit: Ken Caldeira
by Staff Writers
Stanford CA (SPX) Dec 17, 2007
Carbon emissions from human activities are not just heating up the
globe, they are changing the ocean's chemistry. This could soon be fatal
to coral reefs, which are havens for marine biodiversity and underpin
the economies of many coastal communities. Scientists from the Carnegie
Institution's Department of Global Ecology have calculated that if
current carbon dioxide emission trends continue, by mid-century 98% of
present-day reef habitats will be bathed in water too acidic for reef
growth.
Among the first victims will be Australia's Great Barrier Reef, the
world's largest organic structure.
Chemical oceanographers Ken Caldeira and Long Cao are presenting their
results in a multi-author paper in the December 14 issue of Science* and
at the annual meeting of American Geophysical Union in San Francisco on
the same date. The work is based on computer simulations of ocean
chemistry under levels of atmospheric CO2 ranging from 280 parts per
million (pre-industrial levels) to 5000 ppm. Present levels are 380 ppm
and rapidly rising due to accelerating emissions from human activities,
primarily the burning of fossil fuels.
"About a third of the carbon dioxide put into the atmosphere is absorbed
by the oceans," says Caldeira, "which helps slow greenhouse warming, but
is a major pollutant of the oceans." The absorbed CO2 produces carbonic
acid, the same acid that gives soft drinks their fizz, making certain
minerals called carbonate minerals dissolve more readily in seawater.
This is especially true for aragonite, the mineral used by corals and
many other marine organisms to grow their skeletons.
"Before the industrial revolution, over 98% of warm water coral reefs
were bathed with open ocean waters 3.5 times supersaturated with
aragonite, meaning that corals could easily extract it to build reefs,"
says Cao. "But if atmospheric CO2 stabilizes at 550 ppm -- and even that
would take concerted international effort to achieve -- no existing
coral reef will remain in such an environment." The chemical changes
will impact some regions sooner than others. At greatest risk are the
Great Barrier Reef and the Caribbean Sea.
Carbon dioxide's chemical effects on the ocean are largely independent
of its effects on climate, so measures to mitigate warming short of
reducing emissions will be of little help in slowing acidification, the
researchers say. In fact, impending chemical changes may require
emissions cuts even more drastic than those for climate alone.
"These changes come at a time when reefs are already stressed by climate
change, overfishing, and other types of pollution," says Caldeira, "so
unless we take action soon there is a very real possibility that coral
reefs - and everything that depends on them -will not survive this
century."