The ocean has been our savior. Coral doctor sounds the alarm about more acidic seas.

24/8/2010 Guardian Besides generating about two thirds of the oxygen we breathe, oceangoing phytoplankton -those floating microscopic plants that form the base of the aquatic food chain — absorb about a third of all the carbon dioxide we pump
into the atmosphere. In this way, the oceans have managed to slow the buildup of
heat-trapping greenhouse gases and stave off even more dramatic warming of the
But John Guinotte and colleagues are discovering that the critical role of
“carbon sink” comes at a potentially devastating cost for the world’s oceans:
Guinotte is a coral specialist at the Marine Conservation Biology Institute in
Bellevue, Wash. The changes he sees in ocean chemistry spell trouble for the
coral that he studies closely. If the acidification process continues on its
current trajectory, it poses a dire threat to the whole marine ecosystem.
“What I’m really concerned about with ocean acidification is that we are facing
the prospect of a crash in marine food webs.” says Guinotte. “There is no
question that many of my colleagues in marine science are scared about what is
happening. We know we need a more precise understanding of the changes and
biological responses now under way — and we need it as quickly as possible,
before it is too late to turn things around.”
Guinotte has dedicated his life to the study of coral, especially the less well
understood deep-sea varieties. Growing up in rural Kansas, his only exposure to
corals was through the pages of National Geographic. But that changed when he
learned to scuba dive at his grandfather’s winter home in the Florida Keys. The
experience, plus his interest in biology and geography, led him to Australia,
where he earned his Ph.D.
Guinotte still remembers the thrill of exploring Australia’s Great Barrier Reef
for the first time. “I was absolutely blown away by the abundance and diversity
of coral,” he recalls. At that time, back in the late-1990s, scientists were
increasingly concerned about coral bleaching caused by environmental stresses
such as warming ocean temperatures. Those threats remain, Guinotte says, but
ocean acidification may be an even more serious and intractable problem.
On the macro scale, Guinotte explains, the chemistry of ocean acidification is
relatively clear. Based on some 25 years’ worth of measurements scientists know
that oceans absorb about 22 million tons of carbon dioxide every day. The oceans
are vast. But even so, the absorption of CO2 is now occurring at such an
unprecedented rate that ocean chemistry is approaching a state not seen in many
millions of years. Guinotte fears that many marine species might be unable to
adapt quickly enough to survive these dramatic changes.
As carbon dioxide is absorbed by seawater, hydrogen ions are released. This
lower the pH, making the water more acidic. Measurements indicate that Earth’s
oceans are already about 30 percent more acidic than they were before the
industrial revolution. As the number of hydrogen ions has risen, the number of
carbonate ions available in seawater has gone down. This carbonate deficit makes
life more difficult for the “marine calcifiers,” species such as coral and
shellfish that use carbonate to build their skeletons and protective shells.
“Ocean water becomes increasingly corrosive to calcium carbonate,” says
Guinotte. “A reduction in carbonate ions not only impedes corals’ ability to
build their skeletons, but once the calcium carbonate drops below critical
levels, the ocean erodes the framework they have built up previously — the
reefs upon which corals live.” Even if select coral species can survive ocean
acidification, Guinotte says, when the coral reefs begin to dissolve, the
effects on the entire marine ecosystem are likely to be devastating.
Scientists know from the fossil record that reefs which sustained damage from
high atmospheric concentrations of CO2 in the geologic past took millions of
years to recover. “Given that we need to think in human time scales, it means
we’re playing for keeps here,” says Guinotte. “To me, it sometimes seems like a
school bus full of children heading for a cliff. Somehow we have to slow it down
enough to find some real solutions.”
Because of the very clear potential for ocean acidification to effect everything
from the tiniest oxygen-providing phytoplankton to the larger fish that feed in
the coral reefs — or, as Guinotte has written, “from the shallowest waters to
the darkest depths of the deep sea” — the threat to humankind is immense.
To figure out precisely how much acidification many varieties of coral can
tolerate, and what we can do to preserve the health of the marine ecosystem,
Guinotte argues for a coordinated research effort that tackles every aspect of
the problem. That includes better monitoring of ocean carbon; closer tracking of
calcifying organisms and more laboratory and field studies of their
physiological responses to increasingly acidicity; and more detailed studies
that model the threat to the marine ecosystem as a whole. Some of this work is
under way, but too much of it has been conducted in piecemeal fashion. Only a
more intensive, coordinated effort, says Guinotte, can provide the detail
necessary for policymakers to develop strategies that protect critical species,
habitats, and ecosystems.
“From the standpoint of the oceans,” Guinotte says, “there is no escaping the
fact that we are going to need major reductions in our CO2 emissions -
something like 80 to 90 percent. When we see governments arguing about
reductions of 10 to 15 percent, I think all of us in the marine science
community need to say that CO2 reductions of this scale are simply not going to
be sufficient. We have to get off fossil fuels.”
The fossil record shows that high CO2 concentrations have likely played a big
role in mass extinctions of marine life in the past. “If marine systems start to
crash, it may well be too late to stop the train,” says Guinotte. “Governments
are likely to panic and make irrational decisions; international tensions could
certainly heat up. These are the kinds of things that keep me awake at night. I
continue to hope we can get it turned around. But it will take political will,
and so far, that has been in short supply.”Printable versionSend to a
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