Shankar IAS: Summary of Ocean Acidification - Famous Books for UPSC Exam (Summary & Tests)

• Oceans are an important reservoir for CO₂, absorbing a significant quantity of it (one-third) produced by anthropogenic activities and effectively buffering climate change,
• Ocean acidification is the change in ocean chemistry - lowering of ocean pH (i.e. increase in concentration of hydrogen ions) driven by the uptake of carbon compounds by the ocean from the atmosphere.

Effect of ocean acidification

• Seawater absorbs CO₂ to produce carbonic acid (H₂CO₃), bicarbonate (HCO_3--) and carbonate ions (CO_32-).
• These carbonate ions are essential to the calcification process that allows certain marine organisms to build their calcium carbonate shells and skeletons ; e.g. hard tropical corals, cold water corals, molluscs, crustaceans, sea urchins, certain types of plankton, lobsters, etc).
• However, increases in atmospheric CO₂ levels lead to decrease in pH level, increase in the concentration of carbonic acid and bicarbonate ions, causing a decrease in the concentration of carbonate ions.
• Thus carbonate ions are less available and calcification is therefore harder to achieve, and may be prevented altogether. Imagine trying to build a house while someone keeps stealing your bricks.
• This impact of ocean acidification may therefore have potentially catastrophic consequences for ocean life and many marine species of economic importance.

Mitigation

• Reducing CO₂ 
• promoting government policies to cap CO₂ emissions,
• eliminate offshore drilling,
• by advocating for energy efficiency and 
• Alternative energy sources such as wind power, solar, etc.

Saturation horizons

• Deep, cold ocean waters are naturally under saturated with carbonate ions causing the shells of most calcifying organisms to dissolve. 
• Surface waters are over saturated with carbonate ions and do not readily dissolve shells of calcifying organisms.
  (a) The saturation horizon is the level below which calcium carbonate minerals undergo dissolution.
  (b) Those organisms that can survive below the saturation horizon do so due to special mechanisms to protect their calcium carbonate from dissolving.
  (c) As ocean acidification causes this horizon to rise vertically in the water column so more and more calcifying organisms will be exposed to under saturated water and thus vulnerable to dissolution of their shells and skeletons.
• The saturation horizon of calcite occurs at a greater ocean depth than that for aragonite, but both horizons have moved closer to the surface presently when compared to the 1800s.