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The Living Oceans

Oceans cover about three quarters of Earth's surface and are slowly rising at an overall rate of about 1 millimeter a year. The average salt content of the ocean is 3.5 percent. Sodium Chloride (NaCl) is the most common salt compound. Ocean organisms have adapted to this saltiness. Ocean salts such as calcium carbonate are used to create bones, teeth and shells. The freezing point of ocean water is -2°Celsius. To survive, some animals have natural antifreeze in their bodies.

Most ocean waves are caused by winds blowing from the same direction. Once waves form they can travel hundreds of miles until they come to shore. The interactions of waves on shorelines are responsible for many shoreline formations. The mechanical weathering caused by water bashing one rock against another eventually can turn boulders into fine sand. The waves can create the wave-cut benches that can be seen on the mountainsides throughout the Wasatch front, created by the ancient Lake Bonneville. Waves can also form interesting structures such as sea stacks, which are large columns of bedrock sticking up in the wave-cut bench.
The link shows a simulation of a wave cut bench shoreline. Notice that the waves wash away sand. When the water recedes, it leaves the cut bench, which almost looks like a cliff.

Waves that hit beaches at angles can cause longshore currents. These currents move mostly parallel with the coastline. Longshore currents can move large amounts of sediments, forming structures such as longshore bars, barrier islands and spits.

Prevailing winds cause global surface currents. These currents form regular moving rivers in the ocean. Global surface currents may move as much as 100 kilometers a day and transfer water of different temperatures. As a result these currents affect worldwide weather patterns and climate. For example the Gulf Stream carries warm water up the east coast of the United States and causes the warming of northern coastal areas of the United States and Canada. One of the best known effects, the El Niño/La Niña cycle, has caused variations in the Pacific equatorial current, changing worldwide weather patterns.
When winds push surface water away from shorelines, they cause upwelling waters rich in nutrients. This results in abundant life off the west coasts of North and South America.
Deep ocean currents are mainly caused by differences in water density. Cool water is denser than warm water. Water higher in salinity is denser than water of lower salinity. This causes the more dense water to flow under the less dense water.  This link provides a video model of the density current caused by temperature. Another density flow, turbidity current, form as seawater mixed with sediment flows down a continental slope, sometimes even forming underwater canyons. The link here provides a video that models a turbidity current.
Tides are caused by the gravitational pull of the moon and the sun on Earth's oceans. The ocean level rises as the moon and/or sun attract water, pulling it up on both sides of Earth. Low tide ebbs at a 90° angle from high tides. This results in life forms in tidal zones (between high and low tides) needing to survive both in water and in air. Tides may change many feet, with great tidal flows in and out of bays and estuaries.
Visit NASA and check out some great oceanography images from space!
The ocean averages over two miles in depth. The underwater terrain varies from cliffs that are miles high to abyssal plains that form thousands of miles of flat terrain. There are volcanoes such as Hawaii that raise miles from the ocean floor and deep trenches that are more than seven miles deep. The greatest mountain range in the world, called the mid-ocean ridge, wraps around Earth for over 40,000 miles. It is comprised of volcanoes and great faults. The hydrothermal, or hot water, vents on this ridge create food chains based on use of chemical energy, instead of photosynthesis, from these vents.
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Updated October 24, 2008 by: Glen Westbroek

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