Ocean Acidification Sonya Remington

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.

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

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

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 CO 2 from the atmosphere. Phytoplankton - Forams

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

Why is Ocean Acidification Occurring? 1 Gt = 10 9 metric tons = grams 1 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 CO 2 ?

When CO 2 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 CaCO 3 shells? H + CO 3 2- How does an increase in H + ions (decrease in pH) affect CaCO 3 shells? H + CO 3 2-

Shell-building organisms need CO 3 2- ions for their CaCO 3 shells: Why does a decrease in CO 3 2- ions spell trouble for organisms ? Ca 2+ + CO 3 2- = CaCO 3 Shell dissolution Sea water “wants” more carbonate, so it “takes” it from the shells of organisms.

Why CaCO 3 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 (CaCO 3 = Ca 2+ + CO 3 2- )

Back to the ocean: Why do CaCO 3 shells dissolve in seawater? Shells are made of CaCO 3 =Ca 2+ + CO 3 2- H + CO 3 2- Shells are made of CaCO 3 = Ca 2+ + CO 3 2- a.The pressure generated by CO 2 gas dissolved in the water causes the CaCO 3 shells to explode. b. The decrease in the pH of ocean water due to the input of atmospheric CO 2 results in and ocean that is saturated in CO c.The ocean is made more acidic when CO 2 from the atmosphere results in an increase in the H+ ion concentration and an under-saturation of CO 3 2- in the ocean.

Why do CaCO 3 shells dissolve in seawater? 1.Pressure generated by CO 2 2.Decreased pH leads to CO 3 2- saturation 3.Increase in H+ and undersatur- ation of CO 3 2-

Calcite (hexagonal) Aragonite (orthorhombic) All CaCO 3 shells are not created equal 10 g Calcite Aragonite Decreased ocean pH (more acidic water) 8 g 5 g Calcite Aragonite Aragonite is more soluble

All CaCO 3 shells are not created equal OrganismForm of CaCO 3 ForaminiferaCalcite CoccolithophoresCalcite MacroalgaeAragonite or Calcite Corals: warm water cold water Aragonite Pteropod molluscsAragonite CrustaceansCalcite Echinoderms (sea urchin)Calcite

The Solutions What can we do about ocean acidification?

A possible geoengineering solution: Add CaCO 3 to the ocean. Shells are made of CaCO 3 =Ca 2+ + CO 3 2- H + CO 3 2- Shells are made of CaCO 3 = Ca 2+ + CO 3 2- Reduce CO 3 2- under-saturation caused by excess CO 2 dissolving in ocean water. Sounds great, but……………..

To counteract 2 Gt C/yr input of CO 2, would need 20 Gt CaCO 3 /yr. White Cliffs of Dover would be rapidly consumed. Limestone Rock (CaCO 3 ) 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 CO 2 to the atmosphere.

What about Fe fertilization to take care of CO 2 already in the atmosphere? Phytoplankton - Forams Biological Pump

Stop adding CO 2 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 + ) pHH Take Home Message: Small changes in pH represent large changes in H+ concentration.

When CO 2 gas from the atmosphere dissolves in water, H + concentration increases.

All CaCO 3 is not equal – Corals made of aragonite will be more affected Calcite (shellfish, forams) and aragonite (corals) are both CaCO 3 minerals. Same chemical composition: CaCO 3

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