ocean acidification sonya remington [email protected]
Post on 21-Dec-2015
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TRANSCRIPT
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?
How big is the ocean “carbon pool” relative to land and atmosphere?
1 2 3
10%
80%
10%
1. Much smaller.
2. About the same.
3. Much bigger.
According to the May 2008 Seattle Times article, ocean acidification is not confined to the deep ocean due to:
1 2 3 4
8% 6%12%
75%1. Increased
alkalinity
2. Natural upwelling
3. Colder waters
4. Dead plankton
Organisms that building their shells from calcium carbonate are negatively impacted by ocean
acidification due to a decrease in:
1 2 3 4
5%2%
69%
24%
1. Methane dissolution
2. Nitrogen and phosphorous
3. Carbonate ions
4. General happiness
The Consequences
The shells of marine organisms will dissolve.
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
Loss of food sources (fish, shellfish, etc) for subsistence food gathering
Loss of sources of income for local communities, often in developing countries
Fishing
Ecotourism
Decrease in “biological pump” – Removes CO2 from the atmosphere.
Phytoplankton - Forams
The Science
Why ocean acidification is occurring
Why it harms marine organisms
Why is Ocean Acidification Occurring?
1 Gt = 109 metric tons = 1015 grams1 Gt = 40,000 aircraft carriers
Spatial Distribution of Ocean Acidification
What makes ocean waters corrosive to shell-building organisms?
What is pH?
pH = a measurement scale used to quantify the concentration of hydrogen ions (H+)
Acidification or Increased “Corrosiveness” is due to a Decrease in pH.
Take Home Message:
H+ concentration = pH
But what do H+ ions have to do with CO2?
When CO2 gas from the atmosphere dissolves in water, H+ concentration increases.
What makes ocean waters corrosive to shell-building organisms?
How does an increase in H+ ions (decrease in pH) affect CaCO3 shells?
H+ CO32-
How does an increase in H+ ions (decrease in pH) affect CaCO3 shells?
H+ CO32-
Shell-building organisms need CO32- ions for their CaCO3 shells:
Why does a decrease in CO32- ions spell trouble for organisms ?
Ca2+ + CO32- = CaCO3
Shell dissolutionSea water “wants” more carbonate,
so it “takes” it from the shells oforganisms.
Why CaCO3 shells dissolve in seawater
Analogy: Table salt (NaCl) dissolves when you add it to a glass of tap water.
NaCl = Na+ + Cl-
Salt dissolves
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
(CaCO3 = Ca2+ + CO32-)
Back to the ocean: Why do CaCO3 shells dissolve in seawater?
Shells are made of CaCO3 = Ca2+ + CO32-
H+ CO32-
Shells are made of CaCO3 = Ca2+ + CO32-
a. 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 CO3
2-.c. 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 CO3
2- in the ocean.
Why do CaCO3 shells dissolve in seawater?
1 2 3
0%
93%
7%
1. Pressure generated by CO2
2. Decreased pH leads to CO3
2- saturation
3. Increase in H+ and undersatur-ation of CO3
2-
Calcite(hexagonal)
Aragonite(orthorhombic)
All CaCO3 shells are not created equal
10 g
10 g
Calcite
Aragonite
Decreasedocean pH
(more acidic water)
8 g
5 g
Calcite
Aragonite
Aragonite is more soluble
All CaCO3 shells are not created equal
Organism Form of CaCO3
Foraminifera Calcite
Coccolithophores Calcite
Macroalgae Aragonite or Calcite
Corals: warm water cold water
AragoniteAragonite
Pteropod molluscs Aragonite
Crustaceans Calcite
Echinoderms (sea urchin) Calcite
The Solutions
What can we do about ocean acidification?
A possible geoengineering solution: Add CaCO3 to the ocean.
Shells are made of CaCO3 = Ca2+ + CO32-
H+ CO32-
Shells are made of CaCO3 = Ca2+ + CO32-
Reduce CO32- under-saturation caused by excess CO2 dissolving in ocean water.
Sounds great, but……………..
To counteract 2 Gt C/yr input of CO2, would need 20 Gt CaCO3/yr.
White Cliffs of Dover would berapidly 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.
What about Fe fertilization to take care of CO2 already in the atmosphere?
Phytoplankton - Forams
Biological Pump
Stop adding CO2 to the atmosphere
Questions?
What makes ocean waters corrosive to shell-building organisms?
Total Carbonate =
• 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+)
pH H+
1 100000000
2 10000000
3 1000000
4 100000
5 10000
6 1000
7 100
8 10
9 1
10 0.1
11 0.01
12 0.001
13 0.0001
14 0.00001
Take Home Message: Small changes in pH represent large changes in H+ concentration.
When CO2 gas from the atmosphere dissolves in water, H+ concentration increases.
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
What can society do about Ocean Acidification?
1) Stop adding CO2 to the atmosphere
2) 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 beenormous
What is alkalinity?
Natural Upwelling: How deep ocean water reaches the surface
