Correct Option
The correct option is 1 and 3 only.
Explanation
The vertical distribution of ocean temperature is generally divided into three distinct layers: the upper surface layer (warm), the transition layer (thermocline), and the lower deep layer (cold). This stratification varies significantly with latitude.
Statement-wise Analysis
- Statement 1 is Correct: The temperature-depth profile typically shows a boundary region known as the thermocline. This layer lies beneath the surface mixed layer and is characterized by a rapid decrease in temperature with increasing depth. It acts as a transition zone between the warm surface water and the cold deep water.
- Statement 2 is Incorrect: The third layer, known as the deep layer, extends from the base of the thermocline to the ocean floor. This layer is very cold and constitutes the vast majority of the ocean's mass. Approximately 90 % of the total volume of ocean water is found in the deep ocean (below the thermocline), not above it.
- Statement 3 is Correct: In high latitudes, such as the Arctic and Antarctic circles, the surface water temperatures are extremely low (close to 0°C) due to the lack of insolation. Since the deep ocean water is also cold, there is very little temperature difference between the surface and the bottom. Consequently, the vertical temperature gradient is negligible, and the distinct thermocline layer is often absent.
Key Takeaway
Key Takeaway: The thermocline is the zone of rapid temperature decline separating warm surface waters from cold deep waters. It is prominent in tropical and temperate regions but is generally absent in polar regions, where the water column is isothermal (cold from surface to bottom).