(WOE) The World's Oceans Lesson

The World's Oceans

We can't drink the water found in the ocean because of the salt. Oceans of the World: Arctic, Indian, Southern Ocean, Pacific, Atlantic

Salinity

The most abundant salt in ocean water is sodium chloride. Sodium chloride is commonly known as table salt. It's what you use at dinner to salt your food. When salts dissolve in water, they separate into particles called ions. Sodium chloride breaks into sodium ions and chloride ions. Other salt ions that are found in ocean water include magnesium, sulfate, calcium, and potassium.

Salinity is the measure of the amount of solids, or salts, dissolved in seawater. This is measured in grams of dissolved solids per kilogram of water. The proportions and amount of dissolved salts in seawater remain in equilibrium. Recall that ocean water has an average salinity of 35 parts per thousand. That means that some ocean water has higher salinity and other ocean water has lower salinity. Near the ocean's surface, precipitation can dilute ocean water, making it less salty. In areas of the ocean where rivers empty into them, the ocean water around the mouth of the river can have very low salinity compared to surrounding ocean water. Conversely, in hot, dry climates, ocean water can be saltier because evaporation takes away a great deal of water, leaving the salt behind. At Earth's poles, the freezing of seawater can also increase salinity. When ocean water freezes, the water freezes and leaves the salt behind.

Air Pressure, Water pressure increases as depth increases... Water pressure decreases. Gases

Three of the most important gases dissolved in seawater are oxygen, carbon dioxide, and nitrogen. You will find the greatest concentration of dissolved gases near the surface of the ocean. Photosynthesis, a process where organisms make food and oxygen, requires sunlight. Water below 200m contains very little oxygen. Nitrogen is the most abundant dissolved gas in the oceans. Nitrogen is an important building block of tissue in plants and animals.

Changes with Depth

As you go deeper into the ocean, temperature, pressure, and light conditions change. Temperature decreases with depth. That means it gets colder as you go deeper into the ocean. Sunlight near the ocean's surface warms the water. As you dive deeper into the ocean, less and less sunlight can penetrate the water, so it gets colder. Light also decreases with depth. As mentioned earlier, less and less sunlight can penetrate the water as you go deeper into the ocean. As you dive deeper, the ocean gets darker and darker. In the deep ocean zone, there is no light. If you could travel to this part of the ocean, you would need to bring your own light if you wanted to see anything.

Temperature

Oceans have three temperature layers

  • the surface layer
  • thermocline layer
  • deep-water layer

The surface layer is warm because it receives energy from the sun (solar energy). Water near the poles is cooler because the Sun's rays strike the poles at an angle. The thermocline most often begins at a depth of about 200m. Solar energy cannot reach the thermocline, therefore, this water is very, very cold.

Pressure

Like the atmosphere, the oceans are not uniformly mixed but are structured in layers with distinct properties. Pressure increases with depth as the weight of the overlying air and water increase.

Pressure is force exerted by the weight of water above pressing down. Pressure increases continuously from the surface to the deepest part of the ocean. On average, the depth of the ocean floor is 3.8 kilometers. At this depth, pressure is about 400 times greater than air pressure. Pressure increases at the rate of 10 times the air pressure at sea level per 100 meters of depth.

Water pressure increases with depth. That means the pressure gets higher as you go deeper. Pressure in the ocean is caused by the weight of the water above pushing down toward the ocean floor. The deeper you go, the more water is pushing down, so the pressure is higher. This is why humans can only dive to a certain depth in the ocean without special vehicles. The human body can only withstand so much pressure before it becomes injured.

Density

Salt water has a higher density than fresh water. The dissolved salts in ocean water cause a liter of ocean water to have more matter in it, and thus more mass in it, than a liter of freshwater. This higher density contributes to the fact that it is easier to float in ocean water than it is in fresh water. In the Dead Sea, the water is so salty that you can float effortlessly in the water.

Salt water also has a lower freezing point than fresh water. Fresh water freezes at 0 Celsius, but salt water won't freeze until the temperature drops to -1.9 Celsius. The salt prevents ice crystals from forming at temperatures higher than -1.9C. This is why the ocean doesn't freeze during winter unless the temperature gets very cold and stays that way. In Georgia, we just don't see sea ice. It's much too warm for that here.

Watch the following video to learn more about how the oceans temperature, light, oxygen, pressure and nutrients are dependent on depth.

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