Question

Which of the following is a major cause of increasing ocean acidification?

• A. Rising concentration of carbon dioxide
• B. Rising sea level
• C. Eutrophication
• D. Decreasing dissolved oxygen concentrations

Hint:

Ocean Acidification is often called the "Other $CO_2$ Problem" (the first being global warming). It threatens the entire marine food web, especially shell-forming organisms that are the foundation of many fisheries.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question identifies the primary driver behind the lowering of the pH of the Earth's oceans, a process known as ocean acidification.

Step 2: Detailed Explanation:

• The Chemistry of Acidification: When atmospheric carbon dioxide ($CO_2$) increases (due to burning fossil fuels), more $CO_2$ is absorbed by the ocean surface.

• Chemical Reaction: The $CO_2$ reacts with water ($H_2O$) to form carbonic acid ($H_2CO_3$). This acid then dissociates into hydrogen ions ($H^+$) and bicarbonate ions.
\[ CO_2 + H_2O \rightarrow H_2CO_3 \rightarrow H^+ + HCO_3^- \] The increase in $H^+$ ions directly lowers the pH, making the water more acidic.

• Consequences: This process reduces the availability of carbonate ions, which are needed by marine "calcifiers" (like corals, mollusks, and some plankton) to build their shells and skeletons of calcium carbonate ($CaCO_3$).

• Other Options: While rising sea levels and decreasing oxygen are symptoms of climate change, they are not the cause of the acidification chemistry.

Step 3: Final Answer:
Rising concentration of carbon dioxide is the major cause of ocean acidification.