Ocean Acidification (module 11)

Question 1

Identify the control variable and planetary boundary for ocean acidification.

Answer 1

• carbonate ion concentration with respect to aragonite (>80% of pre-industrial aragonite)
• current 84% of the pre-industrial aragonite saturation state

Question 2

Explain how the ocean acidification boundary is linked with the climate change and biosphere integrity boundaries.

Answer 2

climate change - carbon dioxide emissions
- carbon cycle, ocean plays a critical role in regulating earth’s carbon cycle by absorbing CO2 through a process called carbon sequestration
- as CO2 levels increase in atmosphere more CO2 is dissolved into the ocean surface (ocean-atmosphere exchange) - lowers pH of ocean
biosphere integrity - ocean acidification and marine life
- coral reefs and coral bleaching, increased CO2 levels lead to coral bleaching
- marine food webs and trophic interactions
- acidic oceans have less available calcium carbonate for coral, crustaceans, mollusks (base of many food chains)

Question 3

Describe carbon dioxide dissolution and solubility (and their chemistry) in the context of the ocean carbon system.

Answer 3

CO2 (dissolved) + H2O <-> H2CO3 <-> H + HCO3- <-> 2H + CO3 2-
- shells/skeletons made of CaCO3 (calcium carbonate)

Question 4

Explain how the ocean carbon system buffers the ocean against rapid changes in seawater pH.

Answer 4

• If too much carbon dioxide is added to seawater, which creates too much carbonate ions
• reaction shifts back to the left to buffer (uptake of some of the free hydrogen ions) the solution
• buffering helps to keep the acidity of the seawater from dropping

Question 5

Describe geographic differences in ocean acidification using maps.
What is “saturation state with respect to aragonite”

Answer 5

• omega describes the level of saturation of calcium carbonate in seawater
• <1 = conditions are corrosive (undersaturated) for aragonite-based shells and skeletons (bad)
• > 1 = waters are supersaturated with respect to calcium carbonate and conditions are favorable for shell formation
• > 3 coral growth benefits

Question 6

List impacts of ocean acidification on humans.

Answer 6

• reduced shellfish populations
• decline in fish stocks
• economic losses
• impacts on aquaculture
• disruption of food webs

Question 7

List solutions to the ocean acidification issue.

Answer 7

• reduce CO2 emissions
• restore/establish land uses that enhance uptake of atmospheric CO2 by vegetation and soils
• geoengineering ex. fertilizing oceans with iron to cause human-made phytoplankton blooms to take up CO2
• cut fossil fuel emissions

Question 8

Describe concepts of coral growth (extension, density, calcification).

Answer 8

• corals grow by depositing layers of calcium carbonate onto their skeletons
• extension influenced by factors such as light availability, temperature, water quantity, sedimentation
• density refers to compactness of solidity of coral skeletons determined by the amount of calcium carbonate
• calcification - biological process by which corals secrete calcium carbonate minerals to form skeletons which provide structural support and protection for coral polyps

Question 9

Describe saturation state and the overall impact of ocean acidification on coral calcification during the 21st century.

Answer 9

• decline in coral calcification rates in response to increasing CO2 levels and declining saturation rates