The correct answer is option 'B' - Lysocline.

Lysocline is the term used to describe the level below which calcium carbonate minerals undergo dissolution in the ocean. Let's understand this term in more detail:

1. What is the Lysocline?
The Lysocline is a depth in the ocean where the rate of dissolution of calcium carbonate minerals exceeds the rate of production. It is the boundary between the upper layer where calcium carbonate minerals are preserved and the lower layer where they dissolve.

2. Dissolution of Calcium Carbonate Minerals:
Calcium carbonate minerals, such as calcite and aragonite, are found in the shells of marine organisms like corals, mollusks, and foraminifera. These minerals are formed in the upper layers of the ocean where the concentration of dissolved calcium and carbonate ions is high. However, as water gets deeper, the pressure increases and the temperature decreases, causing a decrease in the solubility of calcium carbonate.

3. Factors Affecting Calcium Carbonate Dissolution:
Several factors influence the dissolution of calcium carbonate minerals in the ocean:
- Depth: As mentioned earlier, the pressure and temperature changes with depth affect the solubility of calcium carbonate. Deeper waters have higher pressure and lower temperature, making them more corrosive to the minerals.
- Carbon Dioxide Levels: The concentration of carbon dioxide in seawater affects the acidity of the water. Higher levels of carbon dioxide lead to increased acidity, which promotes the dissolution of calcium carbonate minerals.
- Saturation State: The saturation state of seawater with respect to calcium carbonate minerals also plays a role. If the saturation state is below 1, the water is undersaturated and dissolution occurs. If it is above 1, the water is supersaturated, and precipitation of calcium carbonate occurs.

4. Importance of Lysocline:
The presence of the Lysocline has significant implications for marine ecosystems and the carbon cycle. As calcium carbonate minerals dissolve below the Lysocline, it affects the availability of these minerals for shell-building organisms. This can impact the health and survival of coral reefs, shellfish, and other marine organisms that rely on calcium carbonate structures for protection and support.

In conclusion, the term used to describe the level below which calcium carbonate minerals undergo dissolution in the ocean is the Lysocline. It represents the depth at which the rate of dissolution exceeds production, and factors like depth, carbon dioxide levels, and saturation state influence this process. The Lysocline is important for understanding the impact of ocean acidification on marine ecosystems and the carbon cycle.

The term used to describe the level below which calcium carbonate minerals undergo dissolution in the ocean is "lysocline," as mentioned in the text.