Due to the rapid increase in the concentration of atmospheric carbon
dioxide from the use of fossil fuels, the oceans are rapidly becoming
more acidic. Keeping in mind that, in addition to climate change and
its many profound effects on global ecology, the world’s oceans are
experiencing dramatic changes in pH levels at rates possibly not
experienced since early in the history of the planet when volcanism
was far more prevalent. Ocean acidity is increasing at a rate more
than 100 times faster than the natural variation experienced the last
two to three billion years due to a concomitant and proportional
increase in the concentration of atmospheric CO2 at the hands of
humanity. Throughout earth history there have been changes in ocean
pH, but the speed of current pH changes are probably unprecedented.
If, as the IPCC suggests in Climate Change Emission Scenarios, the
atmospheric concentration of CO2 reaches 800 ppmv by the end of the
21st century, surface water dissolved inorganic carbon could increase
by more than 12% and the carbonate ion concentration could decrease by
almost 60%, with a corresponding decrease in pH of 0.4 pH units in
surface water (Feely et al., 2004).
Most shallow marine organisms construct their shells with high-
magnesium calcite or aragonite, both metastable minerals at earth
surface temperature and pressure. If oceanic pH levels reach the
predicted values, it could surpass the stability fields for even the
biogenically induced precipitation of these minerals, even in the
tropics where warmer water favors supersaturation with respect to
these minerals. This means that biological calcification of the shells
of most marine organisms, many of which have already had their
physiology deteriorate due to increased shallow ocean water
temperatures, might not be possible. As marine ecosystems are
extremely sensitive to temperature and pH changes, the prospect of the
annihilation shell-constructing marine organisms could mean the break
down of the entire ocean ecosystem, which would be utterly disastrous.
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