Ocean Acidification Reid Bergsund and Catherine Philbin Image source: http://blog.lib.umn.edu/garv0057/garvey3203w/baby-mermaid-coral-reef.jpg Reid Bergsund and Catherine Philbin

Problem Ocean absorbs about 1/3 of excess atmospheric CO2 Carbonate buffer system regulates ocean pH Lower ocean pH inhibits calcification for organisms with CaCO3 shells Ocean absorption of atmospheric CO2 is causing the rate of acidification to increase Image source: http://www.noaa.gov/features/climate/coralreefwatch.html Healthy Coral Reef

Ocean Chemistry 101—RealClimate Carbonic acid dissociates and forms bicarbonate (HCO3-) and carbonate (CO32-) and excess hydrogen ions (H+) An increase in hydrogen ions (H+) results in lowering the pH Increasing CO2 decreases carbonate ions and inhibits the calcification reaction CO2 + CO32- + H2O ⇔ 2HCO3- Equilibrium reaction for CO2 in water Ca2+ + CO32- ⇔ CaCO3 Image source: Ocean Chemistry 101 Calcification reaction

Ocean Acidification Review—Doney, et al (2009) Understanding impacts of acidification has only been demonstrated in short- term experiments Many questions surround organisms’ ability to adapt to increasing CO2 levels Marine ecosystems are delicate and could be significantly affected by changes in the ocean’s chemical composition Organisms’ responses varied to laboratory ocean acidification

Some Species May Benefit From Ocean Acidification—Iglesias-Rodriguez, et al (2008) Exponentially grew coccolithophore and bubbled air containing various levels of CO2 through the culture mediums Coccolithophore calcification and body volume significantly increased with high levels of aqueous CO2 Technical comment questions experimental methods

Question to Keep in Mind How does increased atmospheric CO2 lower ocean pH? What chemical processes are affected by increased ocean CO2 uptake? What are the implications of demonstrating short- term experiments vs. long-term? Historically, how have ocean biota responded to ocean acidification? How will ocean biota respond to an unprecedented acceleration in ocean acidification?