Coastal Systems - How Ocean Currents Work

Ocean currents are located at both the ocean surface (surface currents) and in deep water below 300 metres (deep currents). They move water both horizontally and vertically and occur at both local and global scales.

The Ocean

The ocean is an interconnected system powered by the forces of wind, tides, Coriolis force, the sun, and water density differences. The topography and shape of ocean basins and nearby land also influences ocean currents. These forces and physical characteristics of both land and ocean affects the size, shape, speed, and direction of ocean currents

Surface ocean currents are typically wind-driven, resulting in both horizontal and vertical water movement.

Horizontal surface currents that are local and typically short term include rip currents, longshore currents, and tidal currents. In upwelling currents, vertical water movement and mixing brings cold water towards the surface while pulling warmer, less dense water downward, where it condenses and sinks. This creates a cycle of upwelling and downwelling.

Deep ocean currents are density-driven and differ from surface currents as they are slower moving.

The global conveyor belt includes both surface and deep ocean currents that circulate the globe in a 1,000-year cycle. The global conveyor belt’s circulation is the result of two processes:

(1) warm surface currents carrying less dense water away from the equator toward the poles, and

(2) cold deep ocean currents carrying denser water away from the poles toward the equator.

The ocean’s global circulation system plays a key role in distributing heat, regulating weather and climate, and cycling nutrients and gases around the earth.