[Coral-List] Climate change and coral reef sequestration of carbon

James Cervino PhD. jcervino at whoi.edu
Sat Dec 8 08:06:39 EST 2007

Message From Tom Goreau at the Global Warming Conference:

I can't post to the server, so please post the following on my behalf. I'm a
delegate at the UN Climate Change Conference, busy shootng down many false and
erroneous claims like the one that reefs are a carbon sink. Yhey are

Not only is the entire claim that coral reefs are a CO2 sink completely
incorrect, they are in fact a source of CO2 to the atmosphere even while they
remove carbon from the ocean. This has been understood by carbonate chemists
for a very long time  but we keep having to deal with this popular error over
and over again. 

Fundamentally, because the ocean is a pH buffered system in which electrical
charge is conserved, for every atom of bicarbonate in seawater that is
converted to carbonate and deposited as limestone one molecule of bicarbonate
is converted to carbonic acid and then to CO2 to balance the charge. So in
effect for each atom of carbon removed from the ocean into limestone, one atom
is released as CO2 to the atmosphere.

On a geological time scale limestone deposition and volcanic emissions are the
two major sources of atmosheric CO2 (since photosynthesis and respiration plus
decomposition balance),and are balanced by the fact that CO2 dissolves in fresh
water, where it is the major acid once it ionizes, and is then neutralized by
chemical weathering of limestone on land and of igneous and metamorphic rocks,
being converted into bicarbonate which washes into the sea, resuming the cycle.
Half of all the limestone buried in the sea is buried in coral reefs (since most
 ooceanic production dissolves in the deep sea), but to put it into
perspective, this natural source of CO2 is 50 TIMES SMALLER THAN FOSSIL FUEL
INPUTS, showing how seriously we have perturbed the natural carbon cycles.

The only way that reefs could be a CO2 sink would be if they were autotrophic
ecosystems that buried most of the algae carbon before it could decompose. But
in fact reef sediments have very low buried organic carbon content, because the
organic carbon is almost entirely decomposed. In fact, reefs are not autotrophic
at all, they are heterotrophic systems that rely on external organic carbon
input from land and oceanic zooplankton.

Whenever I have measured oxygen in a reef it has always been below saturation,
except directly over dense shallow seagrass beds in full sunlight. Overall the
reef organic carbon cycle is consuming oxygen and producing CO2,  as well as
the CO2 produced by limestone deposition. 

  Coral reefs are the
first and worst victims of global warming, but they do not contribute to
removing CO2 form the atmosphere at all. We must save them for their
biodiversity, fisheries, shore protection, and tourism services, not because of
false and misqguided claims that they are carbon sinks.

Tom Goreau
  President, Global Coral Reef Alliance

Dr. James M. Cervino
Pace University & Visiting Scientist
Woods Hole Oceanographic Inst.
Department of Marine Chemistry
Woods Hole MA.
Cell: 917-620*5287

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