Earth’s Oceans

Some facts… Over 70% of the Earth’s surface is Ocean. That’s about 360 million square km. Ocean water is different than fresh water; How? It is salty. The ocean has many dissolved salts in it with the greatest amount coming from sodium and chlorine. When Sodium (Na) and Chlorine (Cl) combine it forms a salt called halite, which is the common table salt used to season food.

What’s the big deal about the ocean being salty? When we talk about how salty the ocean is we use a term called salinity. The Ocean water has an average of 3.5% dissolved salts. From the 3.5%, 30.6% is sodium, and 55% is chlorine.

We can’t drink saltwater This is a main reason we learn about the salinity of oceans. 97% of all water is salt water, and from the remaining 3% fresh water, only 1% is readily available. Some parts of the ocean, like in the Red Sea, can have a salinity as high as 4.1%. This is due to the high evaporation rate.

What other effects does the salinity have? Salt also causes water to freeze at lower temperatures, and makes the water more dense. The more dense the water is, the easier it is for things to float. The temperatures of the water determine the type of life that can exist in a given region.

What else is in the ocean water besides salts? Oceans also contain dissolved gasses. Can you name a gas that is in oceans? 1.Oxygen 2.Carbon dioxide 3.Nitrogen

So where does all the salt come from? The salts come from mainly dissolved rocks and soils that rivers and runoff water bring to oceans. Volcanic eruptions also have deposited salts in oceans.

What about the gasses? Oxygen comes from the atmosphere, and from organisms that photosynthesize. Note: Photosynthesis is how plants use the sunlight’s energy for food, and gives off oxygen in return.

Carbon dioxide also comes from the atmosphere, and from organisms when they respire (breathe). Nitrogen comes from the atmosphere.

Is it possible… To go all around the world by ship and never touch land? Yes! While we have made imaginary boundaries for the oceans, they are all actually connected. Can you name all the oceans from the largest to the smallest? Hint: There are 5.

Located between the Southern Ocean, Asia, Australia, and the Western Hemisphere

Located between Africa, Europe, the Southern Ocean, and the Western Hemisphere

Located between Africa, the Southern Ocean, Asia, and Australia

Located between 60 degrees south latitude and Antarctica

Located between Europe, Asia, and North America, mostly north of the Arctic Circle

So, now we know what ocean water is made of, and where the oceans are… What do you know about the ocean floor? Is it flat? Is it rocky? Is it sandy? Is it deep? How Deep? Let’s draw a picture.

An ocean floor example

Ocean floor Features Ocean Basin- This is the actual depression in Earth’s surface that holds the ocean water

Continental Shelf The gradual sloping end of a continent that extends under the ocean

Continental Slope The continental slope drops more steeply, and extends from the outer edge of the shelf to the ocean floor

Seamount These are underwater mountains/volcanoes that do not break the surface of the ocean.

Abyssal Plains The abyssal plain is some of the deepest parts of the ocean, and some of the flattest parts of Earth

Volcanic Islands What is the tallest mountain in the world?

If you said Mt. Everest… You’re WRONG!!! While Everest is the “Highest” (above sea level), the volcanic mountain island Mauna Kea is actually taller from base to peak! Mt. Everest is 8,848 m (29,028 ft), but Mauna Kea is 10,203 m (33,476 ft) from it’s base in the Pacific ocean.

A Volcanic Island Is formed by volcanic eruptions. The lava continues to pile up and harden and the mountain/island breaks the surface of the ocean.

Mid ocean Ridge

The Mid Ocean Ridge Is between 70,000 and 80,000 km long Is a continuous chain of undersea mountains that runs all around the world Is the longest mountain chain on Earth Forms new ocean floor as lava erupts through the Earth’s crust

What causes the Mid Ocean Ridge? Parts of Earth’s crust—which are called crustal plates—are constantly moving. When these plates spread apart, they allow the hot magma to enter the ocean floor. As it enters the ocean and cools, it solidifies, and forms new ocean floor.

Trenches Trenches are like canyons on the bottom of the ocean floor. They are some of the deepest parts of the earth. Some bottoms of trenches haven’t even been explored yet.

The Mariana Trench This is the deepest trench we know of; it is over 11km deep. It is located in the Pacific Ocean. Most trenches are in the Pacific Ocean. Mt. Everest could easily fit in the Mariana Trench, and there would still be over 2000m of water over it!

How deep is the ocean? The depth of the ocean is extremely variable. The Ocean has an average depth between 3 and 4 kilometers. The deepest point we know of is the Mariana Trench (about 11km).

How do we know how deep the ocean is? There are several methods that have been used; can you think of any? - sounding - SONAR - diving - submersibles - Remote Underwater Manipulator - Satellites - Gravity Mapping

Some picture examples

Did you know we map the ocean floor? Why do we map it? So ships know the best travel routes. So we can understand the different depth of the ocean and the different effects it has on life, as well as the minerals that are available. So we can better understand the formation of the Earth, and all of the valuable resources it has.

The type of map we use is called a Topographic Map Topography is the study of the layout of the land. How is this different than a regular travel map? Where else would you use a topographic map? How do they work? Road map Topographic map

Ocean Floor Topography When we discussed all the different sections of the ocean floor, we were discussing the subsurface topography of the ocean.