Final answer:
The thermocline is a transitional layer of the ocean characterized by rapidly decreasing temperatures with depth. It separates the warm surface water from the cold, deep water in the ocean.
Step-by-step explanation:
The thermocline is a transitional layer of the ocean characterized by rapidly decreasing temperatures with depth. It is a part of the oceanic zone, which begins offshore where the water measures 200 m deep or deeper.
The thermocline is significant because it separates the warm surface water from the cold, deep water in the ocean.