Introduction

The ocean is not a still body of water. It is constantly in motion, driven by a combination of its own internal properties and external forces. The physical characteristics of ocean water — temperature, salinity, and density — along with external forces like the gravitational pull of the sun and moon and the action of winds, all influence how and why ocean water moves.

These movements take two broad forms: horizontal and vertical. Horizontal motion refers to ocean currents and waves, while vertical motion refers to tides. Both types are common across all ocean water bodies.

Ocean currents are the continuous flow of a huge amount of water in a definite direction. Think of them as rivers within the ocean, moving water from one place to another along a set path. Waves, on the other hand, are also horizontal motion, but they work differently. In a wave, the water itself does not actually travel forward — it is the wave train that moves ahead. The individual water particles mostly rise and fall in place, passing energy along, while the current physically transports water from one location to another.

Vertical motion refers to the rise and fall of water in the oceans and seas. The most familiar example is the tide. Because of the gravitational attraction of the sun and the moon, ocean water is raised up and then falls down twice a day. This rhythmic rise and fall is a direct result of these celestial pulls.

Vertical motion is not limited to tides. It also includes the upwelling of cold water from the subsurface and the sinking of surface water. These processes move water vertically within the ocean column and are important parts of the ocean's overall circulation.