How does ocean temperature vary with depth?

How does ocean temperature vary with depth?

• A. Constant temperature
• B. Warmer at surface, colder with depth
• C. Warm at both surface and depth
• D. Colder at surface, warmer with depth

Answer: (B)

The main idea here is how solar heating and water layering shape ocean temperature with depth. Sunlight heats the surface water, so the top layer becomes warmer than the water below. Water absorbs most of the sun’s energy in the upper few tens to hundreds of meters, and limited mixing keeps this heat there. As you go deeper, you move away from that heat source, so temperatures fall, often quickly in the transition zone, and level off in the deep ocean where waters are near freezing. So, the usual pattern is warm at the surface and colder with depth. This fits the idea that temperature isn’t constant with depth, and it isn’t colder at the surface or warmer with depth. The surface-to-depth gradient explains why the correct choice describes the ocean as warmer at the surface and colder as you go deeper.

The main idea here is how solar heating and water layering shape ocean temperature with depth. Sunlight heats the surface water, so the top layer becomes warmer than the water below. Water absorbs most of the sun’s energy in the upper few tens to hundreds of meters, and limited mixing keeps this heat there. As you go deeper, you move away from that heat source, so temperatures fall, often quickly in the transition zone, and level off in the deep ocean where waters are near freezing. So, the usual pattern is warm at the surface and colder with depth.

This fits the idea that temperature isn’t constant with depth, and it isn’t colder at the surface or warmer with depth. The surface-to-depth gradient explains why the correct choice describes the ocean as warmer at the surface and colder as you go deeper.