Density differences in the oceans are produced by ___ heating.

• A. Uniform heating
• B. External heating
• C. Uneven heating
• D. Radiant heating

Answer: (C)

Density in the ocean is largely controlled by temperature: cooler water is denser than warmer water. The Sun’s heat doesn’t reach all parts of the ocean equally, so heating varies by location, depth, and time. This uneven heating creates a map of temperature differences—some areas become cooler and denser, others warmer and lighter. These density differences drive vertical sinking where water is dense and horizontal flows as waters move to balance contrasts. If heating were uniform, the temperature, and hence the density, would be similar everywhere, producing far weaker density-driven circulation. Radiant heating describes solar input, which causes heating, but the important point here is that its uneven distribution creates the density gradients that drive ocean circulation.