What measure describes how hot or cold water is, generally decreasing with depth?

• A. Salinity
• B. Light
• C. Temperature
• D. Turbidity

Answer: (C)

Temperature is the measure of how hot or cold water is, and in many aquatic systems it generally decreases with depth because sunlight heats the surface and deeper waters receive less warming. This creates a warmer surface layer and much colder water below, often with a noticeable change in temperature known as a thermocline. Salinity is about salt content, not heat; light refers to radiant energy that diminishes with depth but isn’t a heat measure; turbidity describes how clear or cloudy the water is, not its temperature. So the property that best describes how hot or cold water is—and that typically drops as you go deeper—is temperature.