Ocean Currents, Waves, and Tides Explained

Ocean Currents and Their Classifications

Ocean currents are organized and continuous movements of water inside the ocean. There are two primary types of ocean currents.

Surface Currents

Surface currents are currents that flow in the upper 400 meters of the ocean. The main cause is the winds and the influence of Earth's rotation. Warm currents originate at the equator, where the sun heats the water (e.g., the Gulf Stream). Cold currents originate from polar regions and transport cooler water toward the tropics (e.g., the Peru Current).

The Role of Gyres

A gyre is a circular system of surface currents created by the combination of winds and Earth's rotation. A gyre flows in a specific direction based on the hemisphere:

• The Northern Hemisphere rotates clockwise.
• The Southern Hemisphere rotates counterclockwise.

Subsurface and Density Currents

A subsurface current, also called a deep ocean current or density current, is a current that flows beneath the surface and is driven by differences in water density. It depends on water temperature and salinity.

The Mechanics of Ocean Waves

Waves are rhythmic back-and-forth motions of water that transfer energy through the water. Waves move in a circular motion.

Wave Anatomy

• The crest: The highest point of a wave.
• The period: The period of time between one wave and another.
• The trough: The depression of water between crests.

Factors Determining Wave Size

The size of a wave is determined by several factors:

• Speed of the wind.
• Length of time the wind blows.
• The expanse of water over which the wind blows (fetch).

An example of a wave type is choppy waves, which are formed by gusty winds; these waves have different sizes and move in several directions.

Why Do Waves Break?

The bottom of the wave slows down because it touches the ocean floor. Then, the top of the wave keeps moving fast and forms a breaker. Consequently, the wave goes forward and collapses, forming a surf.

The Science of Tides

Tides are the most regular and predictable movement of water in the oceans. They are caused by the Moon's gravity, and the Moon causes the rise and fall of the ocean's water levels.

The Lunar Influence and Daily Cycles

Tides happen because the Moon's gravity pulls on Earth. This means that the water on the side of the Earth that is closest to the Moon will be pulled upward, creating a high tide. We also have a daily tide cycle. This means that different places move into the ocean's gravitational pull because of the Earth's rotation. Between the high tides of places that are close to the Moon, the water level drops, creating low tides.