1. Ocean Acidification 1

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. Increased alkalinity Natural upwelling Colder waters Dead plankton
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. Nitrogen and phosphorous Carbonate ions General happiness
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 12

13. Spatial Distribution of Ocean Acidification13

14. 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+)
Take Home Message:
H+ concentration = pH
But what do H+ ions have to do with CO2? 14

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

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

17. 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 = Ca CO32-)
Add more salt (NaCl)
If water under-saturated in Cl-
Water “wants” more Cl- =
More NaCl will dissolve
If water saturated in Cl-
Water has all the Cl- it can handle =
No additional NaCl will dissolve

18. Back to the ocean: Why do CaCO3 shells dissolve in seawater?
Shells are made of CaCO3 =
Ca CO32-
Shells are made of CaCO3 =
Ca 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
Increase in H+ and undersatur- ation of CO32-

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

21. All CaCO3 shells are not created equal
Organism
Form of CaCO3
Foraminifera
Calcite
Coccolithophores
Macroalgae
Aragonite or Calcite
Corals: warm water
cold water
Aragonite
Pteropod molluscs
Crustaceans
Echinoderms (sea urchin)

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 =
Ca CO32-
Shells are made of CaCO3 =
Ca 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. Stop adding CO2 to the atmosphere

26. Questions?
Foraminifera, commonly referred to as forams, are photosynthetic organisms that live in the surface of the ocean and take up CO2 during photosynthesis. The CO2 that they take up during photosynthesis becomes part of their biomass and, therefore, they help remove CO2 from the atmosphere. When they die, they sink to the bottom of the ocean and with them goes the biomass. This overall process helps decrease the amount of CO2 in the atmosphere. However, these organisms will be unable to function properly in more acidic oceans. Earlier in the course you talk about Fe fertilization of the ocean as a means to remove CO2 from the atmosphere. However, if plankton using the Fe (such as forams) can’t function properly, then Fe fertilization will not work. Here you can see the incomplete shell growth and malformed shell plates of foraminifera under more acidic conditions.
The chemical composition of the sea urchin spine is 94 percent mineral (calcium carbonate, magnesium carbonate and silica) and 6 percent organic matter. 26

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

31. The pH change is small: What’s the big deal?
• 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? pH H+ 1 2 3 4
100000 5
10000 6
1000 7
100 8 10 9
0.1 11
0.01 12
0.001 13
0.0001 14
What is pH?
pH = a measurement scale used to quantify
the concentration of hydrogen ions (H+)
pH = - log (H+)
Remember from the last slide that is it the H+ that cause an increase in the acidity of the ocean or the “corrosive” nature of the ocean water to shell- building organisms.
A change in one pH unit is equal to a 10 fold increase in the H+ concentration
Take Home Message: Small changes in pH
represent large changes in H+ concentration. 31

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

33. Same chemical composition: CaCO3
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

34. 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

35. What is alkalinity?

36. Natural Upwelling: How deep ocean water reaches the surface36

38. Figure (click to enlarge): From Ekman spiral
Figure (click to enlarge): From Ekman spiral. (German) Ekman spiral effect. 1:Wind 2:force from above 3:Effective direction of the current flow 4: Coriolis effect. A quote - The diagram on the right shows the forces associated with the Ekman spiral. The force from above is in red (beginning with the wind blowing over the water surface), the Coriolis force (at right angles to the force from above) is in dark yellow, and the net resultant water movement is in pink, which then becomes the force from above for the layer below it, accounting for the gradual clockwise spiral motion as you move down. 38