Oceanography Oceans and Seas

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Define What causes the motion Illustrations

How Ocean Waters Move

Wind and Waves

A wave is the up and down movement of surface water. What moves slower: water or wind? Water! The height of a wave is related to how hard the wind blows. Wind moving over the surface of water causes the surface of the water to move with it. In a wave, energy is what moves across the surface of the water. Water in a wave actually moves in circles, up and down, not forward. The movement of water in waves can be compared to the up and down movement of a rope when it’s shaken.

The top of the wave is known as the crest and the bottom is called the trough. Wave height is the distance from the crest of a wave to the level ocean surface. Wavelength is the distance between two successive waves.

Currents

Great rivers of water that move through the ocean are called currents. Ocean currents, including the Gulf Stream, are caused by wind patterns and the differences in water densities. The density of ocean water depends on salinity, temperature, and sediment content. As cold deep-ocean currents flow, some of its warms and is pushed to the surface by even colder water underneath. This rising of deep water to the ocean’s surface is upwelling. Upwelling carries nutrients that can support large amounts of sea life. Ocean currents affect the mixing of ocean waters. This can affect plant and animal populations. Currents also affect navigation routes. Earth’s rotation causes currents to bend, and not move in straight lines.

There are four different types of currents: surface currents, rip currents, longshore currents, and deep-ocean currents. A surface current is a large ocean current that flows across the surface of the ocean. IT is caused by prevailing winds blowing across the surface. A famous surface current is the Gulf Stream that runs along the east coast of the United States. Rip currents form when ocean waves flow over a sand spit toward a beach and cannot flow background. The waves pile up until a break forms in the sand. This is why you should swim parallel to the beach if you ever get caught in a rip current. Waves striking a shore at an angle create a longshore current. Differences in water temperature or salinity can cause deep-ocean currents.

Tides

Tides are the repeated rise and fall in the level of the ocean. They are caused by the pull of gravity of the sun and the moon on Earth’s waters. The moon has the greatest effect on tides because it is closer to Earth. Its pull is the strongest on the side of the Earth facing the moon. Its pull combines with Earth’s rotation to produce traveling bulges of water. There are normally two high and two low tides each day. The tide difference in Poquoson is around three feet!

	Define	What causes the motion?	Illustrations
Waves	Forward movement of ENERGY. The up and down movement of surface water	Created by wind
Tide	The rise and fall in the level of the ocean	Gravitational pull of the moon and the sun on the Earth as it rotates	Sketch object at low and high tide
Current	A stream of water that flows like a river through the ocean; moves water forward	Created by the sun warming ocean layers in certain areas like at the equator. The warmer water expands slightly and the warm water runs downhill toward the poles.	Draw water moving in one direction.

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