Transcript PPT

Ocean Acidification
Sonya Remington
[email protected]
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. Much smaller.
2. About the same.
3. Much bigger.
80%
10%
1
10%
2
3
According to the May 2008 Seattle Times article, ocean
acidification is not confined to the deep ocean due to:
1. Increased
alkalinity
2. Natural upwelling
3. Colder waters
4. Dead plankton
75%
12%
8%
1
6%
2
3
4
Organisms that building their shells from calcium
carbonate are negatively impacted by ocean
acidification due to a decrease in:
1. Methane
dissolution
2. Nitrogen and
phosphorous
3. Carbonate ions
4. General
happiness
69%
24%
5%
1
2%
2
3
4
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 grams
1 Gt = 40,000 aircraft carriers
Spatial Distribution of Ocean Acidification
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?
What makes ocean waters corrosive to shell-building organisms?
When CO2 gas from the atmosphere dissolves in water, H+ concentration increases.
H+
CO32-
How does an increase in H+ ions (decrease in pH) affect CaCO3 shells?
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.
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-)
Add more salt (NaCl)
If water under-saturated in ClWater “wants” more Cl- =
More NaCl will dissolve
If water saturated in ClWater has all the Cl- it can handle =
No additional NaCl will dissolve
Back to the ocean: Why do CaCO3 shells dissolve in seawater?
2+
2Shells
3 32Shells are
are made
made of
of CaCO
CaCO33 =
= Ca
Ca2+ ++ CO
CO
H+
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 CO32-.
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 CO32- in the ocean.
Why do CaCO3 shells dissolve in seawater?
1. Pressure
generated by CO2
2. Decreased pH
leads to CO32saturation
3. Increase in H+
and undersaturation of CO32-
93%
0%
1
7%
2
3
All CaCO3 shells are not created equal
Aragonite
(orthorhombic)
Calcite
(hexagonal)
Aragonite is more soluble
Calcite
Aragonite
10 g
10 g
Decreased
ocean pH
(more acidic water)
Calcite
Aragonite
8g
5g
All CaCO3 shells are not created equal
Organism
Form of CaCO3
Foraminifera
Calcite
Coccolithophores
Calcite
Macroalgae
Aragonite or Calcite
Corals:
Aragonite
Aragonite
warm water
cold water
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.
Reduce CO32- under-saturation caused by excess CO2 dissolving in ocean water.
2+
2Shells
3 32Shells are
are made
made of
of CaCO
CaCO33 =
= Ca
Ca2+ ++ CO
CO
H+
Sounds great, but……………..
CO32-
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.
What about Fe fertilization to take care of CO2 already in the atmosphere?
Biological Pump
Phytoplankton - Forams
Stop adding CO2 to the atmosphere
Questions?
What makes ocean waters corrosive to shell-building organisms?
Total Carbonate =
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
pH
H+
1
100000000
2
10000000
3
1000000
pH = a measurement scale used to quantify
the concentration of hydrogen ions (H+)
4
100000
5
10000
pH = - log (H+)
6
1000
7
100
8
10
9
1
10
0.1
11
0.01
12
0.001
13
0.0001
14
0.00001
What is pH?
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 be
enormous
What is alkalinity?
Natural Upwelling: How deep ocean water reaches the surface