Shankar IAS Test: Ocean Acidification - UPSC MCQ

• Ocean acidification is the change in ocean chemistry - lowering of ocean pH (i.e. increase in the concentration of hydrogen ions) driven by the uptake of carbon compounds by the ocean from the atmosphere.

• As the uptake of atmospheric carbon dioxide by the ocean increases, the concentration of hydrogen ions in the ocean increases, the concentration of carbonate ions decreases, the pH of the oceans decreases and the oceans become less alkaline – this process is known as ocean acidification.

Mitigation

• Reducing CO₂
• Promoting government policies to cap CO₂ emissions
• Eliminate offshore drilling
• By advocating for energy efficiency
• Alternative energy sources such as wind power, solar, etc.

Various factors can locally influence the chemical reactions of CO₂ with seawater and add to the effects of ocean acidification. For example:

• Acid rain can have a pH between 1 and 6 and has an impact on surface ocean chemistry. It has a major effect on ocean acidification locally and regionally but very small globally.
• Eutrophication Coastal waters are also affected by excess nutrient inputs, mostly nitrogen, from agriculture, fertilizers and sewage. The resulting eutrophication leads to large plankton blooms, and when these blooms collapse and sink to the sea bed the subsequent respiration of bacteria decomposing the algae leads to a decrease in seawater oxygen and an increase in CO₂ (a decline in pH).

• 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 a decrease in pH level, an 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 maybe prevented altogether. Imagine trying to build a house while someone keeps stealing your bricks.

The equilibrium between the formation and destruction of ozone, has been upset by the influx of several substances into the atmosphere which reacts with ozone and destroys it.

• The rate at which ozone is being destroyed is much faster than the rate at which it is being formed.
• It implies that there is a significant decrease in the concentration of ozone in a particular region of the atmosphere, hence the name ‘Ozone Depletion’.
• The best example of such an Ozone Depletion is the atmosphere over the Antarctic which has only about 50 per cent of the ozone that originally occurred there. The actual realization of ozone-depletion came only in 1985.

• CFCs molecules are made up of chlorine, fluorine and carbon. Where it is used? They are used as refrigerants, propellants in aerosol sprays, foaming agents in plastic manufacturing, fire extinguishing agents, solvents for cleaning electronic and metallic components, for freezing foods etc.
• Two-thirds of CFC is used as refrigerants while one-third is used as blowing agents in foam insulation products.
• The residence time of CFCs in the atmosphere is estimated to be between 40 and 150 years. During this period, the CFCs move upwards by random diffusion, from the troposphere to the stratosphere. The escape of CFCs The CFCs enter into the atmosphere by gradual evaporation from their source.

• Bromine contains compounds called halons and HBFCs, i.e. hydrobromo fluorocarbons [both used in fire extinguishers and methyl bromide (a widely used pesticide)].
• Each bromine atom destroys hundreds of more ozone molecules than what a chlorine atom does. The BrO further reacts with chlorine monoxide (ClO) to give oxygen (O₂) and free atoms of bromine (Br) and chlorine (Cl). These free atoms can further react with ozone.

Why is the Ozone Depletion predominant at the Antarctic?

• The Antarctic stratosphere is much colder. The low temperature enables the formation of polar stratospheric clouds (PSCs), below 20 km.
• Ozone absorbs sunlight, causing the characteristic increase in temperature with increase in altitude in the stratosphere. If ozone is being depleted, the air becomes cooler, further adding to the favourable conditions for the formation of PSCs and stabilization of the vortex. The vortex is a ring of rapidly circulating air that confines the ozone depletion in the Antarctic region.

The longevity of the Antarctic vortex is another factor, enhancing favourable conditions for the depletion of ozone. The vortex remains, in fact, throughout the polar winter, well into mid-spring whereas the vortex in the Arctic disintegrates by the time the polar spring (MarchApril) arrives.