Ocean Acidification
Just some facts
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CO2 concentrations: preindustrial
280 ppmv 2007 385 ppmv (40%
increase)
pH of ocean: preindustrial 8.21 2005
8.10
pH is expected to drop 0.3-0.4 units
at the turn of the century when CO2
levels are expected to be 800 ppmv
(IPCC)
How does increased atmospheric
CO2 decrease ocean pH?
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Air-sea gas exchanges equilibrates
surface water CO2 in approximately 1
year
Increased aqueous CO2 increases
bicarbonate (HCO3-), and H+
Increased H+ lowers carbonate ion
(CO32-) and pH (pH=-log10[H+])
CO2(aq) + H2O↔H2CO3↔H+ + HCO3-↔ 2H+ + CO32-
Calcifying organisms
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Plankton, corals, and coralline algae
use CaCO3 to form shells and
skeletons
When CO32- concentration is
decreased the saturation state
decreases restricting the ability of
CaCO3 (or shell) formation
Dissolution rates increase as well
Planktonic Calcification
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Major groups: coccolithophores and
foraminifera
Coccolithophores Emiliania huxleyi and
Gephyrocapsa oceanica showed a 25-66%
decrease in calcification when CO2 was
560-840μatm respectively
Calcidiscus leptoporus also showed a
decrease in calcification rates as well as
increased malformations in response to
increased pCO2
Planktonic Calcification
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Symbiot-bearing, planktonic foraminifera,
had a decrease in shell mass with
increased concentration of carbonate ion
Orbulina universa and Globigerinoides
sacculifer experienced a 4-6% and 6-14%
decline in shell mass when exposed to 560
and 740 ppmv CO2 when compared to
preindustrial CO2 levels
Impacts on corals
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Coral bleaching: the loss of color in
corals, due to stress-induced
expulsion of symbiotic unicellular
algae or due to the loss of
pigmentation within the algae
Anthony et al. exposed three coral
species to three different CO2 levels
at low and high temperatures to
determine effect on bleaching
Why this matters
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Corals responsible for high amount of
productivity and bleaching results in
loss of productivity
Disruption in ability to make shells
may lower abundance of algae
Loss of major food source or
community shifts
Impact on corals
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High CO2 dosing (1000-1300 ppm)
led to 40-50% bleaching in crutose
coralline algae (CCA) and Acropora
Intermediate CO2 dosing (520-700
ppm) led to 30% and 20% bleaching
in CCA and Acropora
Present day CO2 (380 ppm) led to a
20% and 10% bleaching in CCA and
Acropora
Impacts on corals
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Effect of CO2 dosing on bleaching had a
stronger effect than that of temperature
High CO2 had a two to threefold increase
in bleaching and temperature had only a
20% increase in bleaching
Lowered pH disrupts photoprotective
mechanisms of symbiots by lowering rates
of photorespiration and capacity for
thermal dissipation
References
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Anthony, K. 2008. Ocean acidification causes
bleaching and productivity loss in coral reef
builders. Enviromental Sciences. 105:1744217446.
Doney, S. 2009. Ocean acidification: The other
CO2 problem. Annu. Rev. Marine. Sci. 1:169-192.
Orr, J. 2005. Anthropogenic ocean acidification
over the twenty-first century and its impact on
calcifying organisms. Nature. 437:681-686.