1. Currents and Climates

2. The Salty Ocean
Salinity is the total amount of dissolved solids (salts) in a sample of water.
Salinity affects the properties of water.
The salinity of ocean water is not always the same. In most parts of the ocean, salinity is between 34‰ and 37‰. Near the mouths of large rivers, salinity is lower because the rivers bring fresh water.

3. The Salty Ocean
Also, ocean water is denser than fresh water. As a result, you can float more easily in ocean water than in fresh water.
Density = ocean water>fresh water>you
Sodium Chloride (NaCl) - table salt - makes up most of the salts in ocean water. There are also other kinds of salts in ocean water.

5. Other Ocean Properties
Ocean organisms use gases in ocean water. Two gases that ocean organisms use are carbon dioxide (CO2) and oxygen. Algae, for example, need CO2 to carry out photosynthesis. Ocean animals need oxygen.
CO2 is about 60x more plentiful in the oceans than in the air. Oceans naturally absorb CO2 from the atmosphere.
Oxygen can come from either the air or as a waste product of the photosynthesis of algae.

6. Other Ocean Properties
The ocean absorbs energy from the sun. Near the equator, the temperature at the surface of the ocean is about 25°C - about room temperature. The farther from the equator you go, the cooler the surface temperature becomes.
The deeper you go in the ocean, the colder and more dense the water becomes. Cold water is, of course, more dense than warm water.

8. Surface Currents
Surface currents, which affect water to a depth of several hundred meters, are driven mainly by winds.
A current is a large stream of moving water that flows through the oceans. Unlike waves, currents carry water from place to place.
Surface currents move in circular patterns in the oceans. Most currents flow east or west, and then turn back to complete the circle.

10. Surface Currents
Earth rotates on its axis. The effect that Earth’s rotation has on the direction of winds and currents is called the Coriolis Effect. The Coriolis effect causes ocean currents and winds to move in circular patterns.
In the Northern Hemisphere, the Coriolis effect causes the currents to turn to the right. In the Southern Hemisphere, the Coriolis effect causes currents to shift to the left.

13. Surface Currents
Currents affect climate by moving cold and warm water around the world. Some currents carry warm water from the equator to the poles (Gulf Stream). Other currents carry cold water from the poles to the equator (California Current). Warm water warms the air above it. Cold water cools the air above it.
Remember that warm air holds more moisture, so warm surface currents usually bring more rain than cold surface currents.

14. Surface Currents
Sometimes, changes in wind patterns and currents occur. Such changes can have big effects on oceans and the land nearby.
One example of a change in wind patterns and currents is El Niño. El Niño is an uncommon climate event that happens every two to seven years in the Pacific Ocean. During an El Niño, warm water moves toward the South American coast (it usually moves AWAY).

17. Surface Currents
La Niña, on the other hand, is a period of colder than normal surface waters in the Pacific Ocean. La Niña is the opposite of El Niño. La Niña brings cold winters and greater precipitation to the Pacific Northwest of the United States.
This reversal of surface currents has planet- wide impacts on weather conditions.

19. Deep Currents
Deep currents are caused by differences in density of ocean water. Deep currents move and mix water around the world. They carry cold water from the poles toward the equator.
The density of water depends on the water’s temperature and salinity. When warm water flows toward the poles, the water gets cooler. Some of the water freezes and becomes ice. When water freezes, it leaves its salts behind. That causes the salinity of the remaining water to increase.
As the water gets colder, and its salinity increases, the water becomes denser. The denser water will sink.

21. Deep Currents
Deep currents, due to their high density, travel very slowly.
The Arctic Bottom Water is so cold and dense that it can take 750 years to travel from the Arctic Ocean to the equator.
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