What factor affects the speed of an ocean current?

The speed of an ocean current is influenced by the density of the water, which is determined by various factors such as temperature and salinity. When the density of water changes, it can lead to differences in buoyancy and, consequently, affect how the water moves. Denser water tends to sink, creating a downward flow, while less dense water rises, contributing to the vertical and horizontal movements that form currents.

Changes in temperature can affect density, but density itself remains the fundamental property that dictates movement. Salinity can also alter water density; for instance, higher salinity increases water density, altering current characteristics.

While air temperature and wind patterns play crucial roles in driving ocean currents, they primarily contribute to surface currents and may not directly correlate with the intrinsic characteristics of the water itself that govern the speed of deeper currents. Thus, density stands out as a significant factor that directly affects the speed of an ocean current, making it the correct answer.