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Ocean Acidification The other CO 2 problem

Ocean Acidification The other CO 2 problem. Keith Hunter Department of Chemistry University of Otago. CO 2 concentrations in dated polar ice cores show that the atmospheric increase began in the mid-18 th century (about 1750).

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Ocean Acidification The other CO 2 problem

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  1. Ocean AcidificationThe other CO2 problem Keith Hunter Department of Chemistry University of Otago

  2. CO2 concentrations in dated polar ice cores show that the atmospheric increase began in the mid-18th century (about 1750). It has been constant around 280 µatm for at least the last 7,000 years.

  3. About half of the fossil fuel CO2 is “missing” from the atmosphere…

  4. Fossil fuels combusted +240 Atmosphere +160 Ocean +120 Land - 40

  5. Penetration of anthropogenic CO2into the ocean Feely et al. Science 2004

  6. As atmospheric pCO2 and free CO2increase, pH and carbonate decrease CO2 + CO32- + H2O → 2 HCO3- Forms of CO2 in water Free CO2 beer, soda water Bicarbonate HCO3- baking soda Carbonate CO32- limestone, washing soda

  7. CO2(g) + H2O + CO32- 2 HCO3-

  8. Initially, carbonate is consumed CO2(g) + H2O + CO32- 2 HCO3- Then calcium carbonate is dissolved CO2(g) + H2O + CaCO3 2 HCO3- + Ca2+ The changeover occurs when CaCO3 becomes undersaturated [Ca2+][CO32-] < Ks

  9. The saturation state controls whether calcium carbonate is stable or not (i.e. whether it dissolves)

  10. pH 8.2 pH 7.4 Corals subjected to acidified water lose their CaCO3 When transferred to normal seawater, they calcify again Fine and Tchernov, Science 2007

  11. Observed and predicted Southern Ocean surface acidification conditions for the 21st century Predicts first “tipping point” for aragonitic organisms by about 2030 McNeil B. I., Matear R. J. PNAS 2008;105:18860-18864

  12. Otago Coastal Transect forpH and pCO2 measurements

  13. Otago Shelf TransectSubantarctic waters Annual pH change Equilibrium -0.0017 (Baring Head CO2 data) Subantarctic -0.0020  0.0017 (standard error, n = 28, probability 80%) Strong seasonal cycle driven by plankton productivity Water is fully acidified in winter Much less so in summer

  14. Spatial Variability 3 different water masses: Neritic (0-18 km), Subtropical (18-32 km) and Subantarctic (> 32 km). Subantarctic water seems to be close to equilibrium with atmospheric CO2 as assumed in global models of CO2 uptake by the ocean. Neritic and Southland Current waters are out of equilibrium, less affected by anthropogenic CO2, i.e. less acidified.

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