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Characteristics of Oceans Help (page 2)

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By — McGraw-Hill Professional
Updated on Sep 4, 2011

Pressure

Although no one really thinks about it, air pushes against us at a constant pressure. At sea level, this pressure is 14.7 pounds per square inch (psi), or 1 kg/cm 2 . Our body handles this constant push, by pushing back with the same amount of force. On the top of a mountain, the pressure is less.

But water is a different story. Water is a lot heavier than air. The pushing force (pressure) goes up when you enter the water. In fact, at 10m in depth, one atmosphere (14.7 psi) pushes down on you.

It’s possible for humans to dive three or four atmospheres with the right scuba equipment, but to go any deeper, tough pressurized vehicles like research vessels and submarines are needed.

Ocean citizens like whales seem to be unaffected by pressure shifts. They chug along in the ocean and dive through rapid pressure changes, all the time, without even thinking about it. Although who really knows what a whale thinks about?

Sperm whales are known to dive to depths of 2250m and can stay down for over an hour. The pressure change from the surface is more than 220 atmospheres! Scientists are still trying to figure out how they do it.

Acoustics

Though Jacques Cousteau titled a book about the sea, The Silent World , the oceans are pretty noisy in places. Where currents smash up against rocky cliffs, the turbulence fills the ocean with sound. However, human ears aren’t sensitive enough to hear all the different frequencies.

Water is a great sound conductor. It doesn’t absorb sound, but allows it to travel great distances before it fades away. The speed of sound through the water is 1450 to 1570 m/s. The travel time increases as the water temperature increases.

Ocean animals are fairly loud. They chatter and call to each other while swimming, squeak when scared, brag when they find food, whistle to send out warnings, ping to inspect their surroundings, and sing to each other on Valentine’s Day. Well, they sing anyway.

Dolphins and whales use a method called echolocation . By emitting a series of clicks and whistles and then listening for the echoes of the sounds bouncing off objects, they can tell where things are. They do this to accurately locate fish, turtles, logs, boats, reefs, and whatever else is around. From the direction and strength of the echo, dolphins and whales get a mental image of their environment. By echolocation, they can tell the size, distance, and direction of objects in their path.

Echolocation is the method used by whales and dolphins to find out what is happening in the ocean around them.

Sonar is also used by oceanographers to study the ocean floor. It works a lot like echolocation. By sending out signals and picking up the echoes, scientists can get a picture of the features of the ocean floor. This is how shipwrecks like the Titanic were located. Fishermen also use sonar to find large schools of fish.

Oceanographers discovered one part of the ocean that has different and better acoustics than other parts of the ocean. It is known as the SOFAR channel , which is short for sonic fixing and ranging channel. In the SOFAR channel, low-frequency sounds can travel for hundreds of kilometers very well. If you rise or go deeper vertically the sound fades much faster. Scientists think that this is the main “long distance telephone line” that whales use to communicate to each other over the ocean’s expanse.

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