PADI Divemaster Certification Practice Exam

What is a thermocline?

1. A layer of warmer water only

2. The interface between layers of different water densities

3. A current of warm water offshore

4. A phenomenon specific to freshwater

The correct answer is: The interface between layers of different water densities

A thermocline represents the interface between layers of water with different temperatures and densities in a body of water, typically found in oceans and large lakes. This layer acts as a barrier that separates the warmer, well-mixed surface water from the colder, denser water below. During diving activities, understanding the thermocline is essential because it can affect both buoyancy and visibility. When divers cross into the thermocline, they may experience a sudden change in water temperature, which can influence their diving comfort and safety. In contrast, the other options do not accurately describe a thermocline. While warmer water layers can exist, a thermocline itself is specifically defined by the transition between differing temperatures and not just a single warmer layer. The suggestion of a warm water current offshore does not capture the true nature of a thermocline, which does not refer to current movement. Lastly, the phenomenon is not exclusive to freshwater; it occurs in saltwater as well, making the characterization as specific to freshwater inaccurate.