1. The oceans are a connected system.
Section 3.1C

2. Ocean water covers most of Earth.
Different sections of the ocean have different names; however, all the sections are connected.

3. How did Earth become covered by an ocean?
Earth formed about 4.6 billion years ago as a ball of molten rock.
Heavier material sank to the core, and lighter materials floated toward the surface.
Water vapor rose to the cooler surface.
About 4 billion years ago, Earth had cooled enough for the water vapor to become liquid.

4. Ocean water contains salts and gases.
The ocean contains all 92 elements that occur in nature, although most are in very tiny amounts.

5. Salts
Salinity is a measure of the amount of dissolved salt contained in water.
The ocean contains many different kinds of salts, but sodium chloride accounts for most of the ocean’s salinity.
Over time, rain and rivers wash some of the elements that make up salts into the sea.
They also enter ocean water when underwater volcanoes erupt.

6. Density
Water that contains dissolved solids, such as salts, is heavier than the same amount of water with no dissolved solids.
Salt water has a greater density than fresh water.
The higher the water’s salt content, the greater its density.
The denser the water, the more easily things float in it.

7. The Dead Sea
The Dead Sea is the lowest place on Earth, roughly 1,300 feet below sea level.
It is fed by the Jordan river, with no outflow.
The quantity of water that evaporates from it is greater than that which flows into it, and this body of water has the highest concentration of salt in the world.

8. The Dead Sea (continued)

9. Some parts of the ocean are saltier than others.
When water evaporates, salt is left behind, and water is saltier.
It is especially salty in shallow areas and warm climates.
Salinity is also higher in areas where ocean water freezes. Ice forms on the ocean, and the salt is left in the water below.

10. Some parts of the ocean are saltier than others (cont.).
Salinity is lower in areas where the ocean is diluted by fresh water.
where rivers empty into the ocean
in areas where a lot of rain falls

11. Oxygen and Other Gases
Oxygen and other gases dissolve in water and are essential to ocean life.
Ocean animals take in oxygen and give off carbon dioxide.
Oxygen and carbon dioxide get mixed into the ocean from the air above the ocean’s surface.
Oxygen is also added by plants and algae that live near the surface.

12. Oxygen and Other Gases (cont.)
Carbon dioxide is a building block of ocean animals’ shells.

13. Ocean temperatures vary.
The Surface Layer:
Heated by the sun and mixed by winds and waves
Warmest layer = less dense = stays at the surface
The Thermocline:
Lies below the surface layer
Temp. drops fast with depth
The deep water
Cold all year
Temp. of the water at the ocean’s bottom is around 0°C-3°C (32°F-37°F), at or barely above freezing

14. Ocean Layers

15. Ocean temperatures vary (cont.).
Surface temp. varies by location and season.
Surface temp is warmer near the equator than near the poles.
Warmer in the summer and cooler in the winter

16. The ocean floor has many features.

17. Continental Shelf
The flat or gradually sloping land that extends underwater from the edge of a continent to a continental slope

18. Continental Slope
Land that drops down steeply a the edge of a continental shelf

19. Submarine Canyons
Cut through the continental shelf and slope

20. Ocean Trenches
Narrow, steep-sided clefts in the ocean floor

21. Abyssal Plain
A wide, flat area of ocean floor that is covered with a thick layer of sediment

22. Seamounts
Undersea mountains

23. Volcanic Islands
Underwater volcanoes tall enough to reach above the surface

24. Mid-ocean Ridge
A chain of mountains that run through an ocean basin

25. Ocean Exploration
Obstacles – pressure, darkness, lack of air, chilling cold
Scuba equipment: can spend about an hour under water; can safely reach depths as great as 40 meters (130 feet)
Deeper: small submarines or robots equipped with cameras

26. Mapping the Ocean Floor
Sonar – a system that uses sound waves to measure distances and locate objects
Ships aim sound waves at the ocean’s bottom and measure the time it takes to receive the echo
Fast echo = bottom is shallow
Slow echo = bottom is deep
Sonar is good to use for detailed images of small areas of the ocean floor.
Satellite imaging is used for large areas.
It can detect tiny bumps and dips in the ocean’s height. Small surface differences reveal the shape of the ocean floor.

27. Mapping the Ocean Floor (cont.)

28. Mapping the Ocean Floor (cont.)