What primarily drives ocean currents?

Ocean currents are primarily driven by differences in temperature and salinity, which affect water density. When water warms up, it becomes less dense and tends to rise, while colder water is denser and sinks. This process is part of the broader thermohaline circulation, which moves water through the oceans based on these temperature and salinity variations.

Additionally, the temperature of ocean water is influenced by solar heating, while salinity can vary due to precipitation, evaporation, and river runoff, leading to the formation of distinct water masses. These variations create gradients that initiate flow, establishing both surface currents driven by wind and deep-water currents driven by density differences.

In contrast, while gravitational pull from the moon does influence tides, it is not the primary driver of regular ocean currents. Volcanic activity under the sea can have localized effects but does not drive the global patterns of ocean currents. Human activity can impact coastal currents through alteration of waterways and pollutant introduction but does not fundamentally drive oceanic currents on a large scale.