Ocean Acidification

1. Ocean Acidification Sonya Remington sunny9@u.washington.edu

2. Today’s Talk on Ocean Acidification • The Consequences: What does ocean acidification mean for natural ecosystems and humans? • The Science: Understand why ocean acidification spells trouble for shell-building organisms. • The Solutions: What can we do about this problem?

3. How big is the ocean “carbon pool” relative to land and atmosphere? • Much smaller. • About the same. • Much bigger.

4. According to the May 2008 Seattle Times article, ocean acidification is not confined to the deep ocean due to: • Increased alkalinity • Natural upwelling • Colder waters • Dead plankton

5. Organisms that building their shells from calcium carbonate are negatively impacted by ocean acidification due to a decrease in: • Methane dissolution • Nitrogen and phosphorous • Carbonate ions • General happiness

6. The Consequences The shells of marine organisms will dissolve.

7. Loss of marine biodiversity • Coral reefs harbor more than 25% of the ocean’s biodiversity – provide a refuge and feeding ground for countless marine organisms. • > 50% of all corals reefs are in cold, deep waters – more impacted by ocean acidification

8. Loss of food sources (fish, shellfish, etc) for subsistence food gathering

9. Loss of sources of income for local communities, often in developing countries Fishing Ecotourism

10. Decrease in “biological pump” – Removes CO2 from the atmosphere. Phytoplankton - Forams

11. The Science Why ocean acidification is occurring Why it harms marine organisms

12. Why is Ocean Acidification Occurring? 1 Gt = 109 metric tons = 1015 grams 1 Gt =40,000 aircraft carriers

13. Spatial Distribution of Ocean Acidification

14. Take Home Message: H+ concentration = pH But what do H+ ions have to do with CO2? What makes ocean waters corrosive to shell-building organisms? Acidification or Increased “Corrosiveness” is due to a Decrease in pH. What is pH? pH = a measurement scale used to quantify the concentration of hydrogen ions (H+)

15. H+ CO32- H+ CO32- How does an increase in H+ ions (decrease in pH) affect CaCO3 shells? How does an increase in H+ ions (decrease in pH) affect CaCO3 shells? What makes ocean waters corrosive to shell-building organisms? When CO2 gas from the atmosphere dissolves in water, H+ concentration increases.

16. Why does a decrease in CO32- ions spell trouble for organisms ? Shell-building organisms need CO32- ions for their CaCO3 shells: Ca2+ + CO32- = CaCO3 Shell dissolution Sea water “wants” more carbonate, so it “takes” it from the shells of organisms.

17. Add more salt (NaCl) If water under-saturated in Cl- If water saturated in Cl- Water “wants” more Cl- = More NaCl will dissolve Water has all the Cl- it can handle = No additional NaCl will dissolve Why CaCO3 shells dissolve in seawater Analogy: Table salt (NaCl) dissolves when you add it to a glass of tap water. Salt dissolves NaCl = Na+ + Cl- (CaCO3 = Ca2+ + CO32-)

18. Back to the ocean: Why do CaCO3 shells dissolve in seawater? Shells are made of CaCO3 = Ca2+ + CO32- Shells are made of CaCO3 = Ca2+ + CO32- H+ CO32- • The pressure generated by CO2 gas dissolved in the water causes the CaCO3 shells • to explode. • b. The decrease in the pH of ocean water due to the input of atmospheric CO2 results in • and ocean that is saturated in CO32-. • The ocean is made more acidic when CO2 from the atmosphere results in an increase • in the H+ ion concentration and an under-saturation of CO32- in the ocean.

19. Why do CaCO3 shells dissolve in seawater? • Pressure generated by CO2 • Decreased pH leads to CO32- saturation • Increase in H+ and undersatur-ation of CO32-

20. All CaCO3 shells are not created equal Aragonite (orthorhombic) Calcite (hexagonal) Aragonite is more soluble 10 g 8 g Calcite Calcite Decreased ocean pH (more acidic water) 10 g Aragonite Aragonite 5 g

21. All CaCO3 shells are not created equal

22. The Solutions What can we do about ocean acidification?

23. A possible geoengineering solution: Add CaCO3 to the ocean. Reduce CO32- under-saturation caused by excess CO2 dissolving in ocean water. Shells are made of CaCO3 = Ca2+ + CO32- Shells are made of CaCO3 = Ca2+ + CO32- H+ CO32- Sounds great, but……………..

24. To counteract 2 Gt C/yr input of CO2, would need 20 Gt CaCO3/yr. White Cliffs of Dover would be rapidly consumed. Limestone Rock (CaCO3) • Limestone mining would be expensive and would cause ecological damage. • All the energy needed to move massive amounts of rock into the ocean would likely add more CO2 to the atmosphere.

25. What about Fe fertilization to take care of CO2 already in the atmosphere? Biological Pump Phytoplankton - Forams

26. Stop adding CO2 to the atmosphere

27. Questions?

31. What makes ocean waters corrosive to shell-building organisms? Total Carbonate =

32. • Seattle Times article: pH changed from 8.1 to 7.6 along Pacific Coast of the US • Turley February 2008 article: Average pH of entire ocean has changed by 0.1 pH units The pH change is small: What’s the big deal? What is pH? pH = a measurement scale used to quantify the concentration of hydrogen ions (H+) pH = - log (H+) Take Home Message: Small changes in pH represent large changes in H+ concentration.

33. When CO2 gas from the atmosphere dissolves in water, H+ concentration increases.

34. All CaCO3 is not equal – Corals made of aragonite will be more affected Calcite (shellfish, forams) and aragonite (corals) are both CaCO3 minerals. Same chemical composition: CaCO3

35. What can society do about Ocean Acidification? • Stop adding CO2 to the atmosphere • Geoengineering • (a) Fe fertilization – removes CO2 from the atmosphere, but may have decreased • effectiveness due to damage to phytoplankton that use • calcium carbonate to build shells • (b) Add alkalinity to the ocean – economic and ecological costs of this would be • enormous

36. What is alkalinity?

37. Natural Upwelling: How deep ocean water reaches the surface