How do surface currents differ from thermohaline circulation in what drives them and their climate impact?

• A. The surface currents are density-driven by temperature and salinity.
• B. The surface currents are wind-driven.
• C. The surface currents transport nutrients only.
• D. The surface currents are wind-driven; thermohaline circulation is density-driven by temperature and salinity.

Answer: (D)

Surface currents are driven primarily by the wind. The wind transfers momentum to the ocean surface, and the Coriolis effect then deflects the flow, creating large, organized gyres that move warm water toward higher latitudes. This wind-driven motion quickly redistributes heat and shapes regional climates, influencing weather patterns near coasts and in the tropics.

Thermohaline circulation, on the other hand, is driven by density differences caused by temperature and salinity. Cold, salty water becomes dense enough to sink in polar regions, setting up a global deep-ocean current that slowly transports heat and dissolved substances around the planet. This deep, long-range circulation has a significant impact on long-term climate patterns and the global distribution of heat, salinity, and nutrients.

Thus, the best description is that surface currents are wind-driven, while thermohaline circulation is density-driven by temperature and salinity.