Question

How do water density differences affect ocean circulation?

Water density differences increase the evaporation rate of ocean water.

Water density differences stop wind-driven surface currents.

Water density differences cause the ocean to freeze at lower temperatures.

Cold, salty water sinks, creating deep ocean currents.

Answer 1

Correct answers: statements 3 and 4 are true; statements 1 and 2 are false.

Brief explanations:
- False — "Water density differences increase the evaporation rate of ocean water.": Evaporation rate is controlled mainly by temperature, humidity, wind speed, and surface salinity to a lesser extent. Density differences themselves do not directly increase evaporation.
- False — "Water density differences stop wind-driven surface currents.": Density differences do not stop wind-driven currents. Surface currents are driven by wind and modified by the Coriolis effect and by density stratification; vertical shear and geostrophic adjustments occur, but the winds still drive surface flow.
- True — "Water density differences cause the ocean to freeze at lower temperatures.": Higher salinity (which increases density) lowers the freezing point of seawater, so saltier/dense water freezes at a lower temperature than fresh water.
- True — "Cold, salty water sinks, creating deep ocean currents.": Cold, salty water is denser and can sink, driving thermohaline circulation (deep currents) such as the global overturning circulation (e.g., formation of North Atlantic Deep Water).