Which layer of thermal stratification is referred to as the middle layer?

The correct choice identifies the layer of thermal stratification known as the metalimnion. In a stratified body of water, layers are distinguished based on temperature gradients. The metalimnion is the layer that sits between the warmer upper layer, known as the epilimnion, and the cooler, denser lower layer, called the hypolimnion.

The metalimnion is characterized by a rapid change in temperature with depth, which is commonly referred to as the thermocline. This layer plays a critical role in the thermal dynamics of the water body, as it acts as a barrier that separates varying temperatures, impacting aquatic life and the distribution of oxygen. Understanding the function of the metalimnion is essential for water quality management and ecological assessments since it influences the biological and chemical processes within the aquatic environment.