1. Chapter 15: Physical Oceanography

2. Importance of Oceans
Oceans are important sources of food, energy, and minerals.
Energy sources such as oil and natural gas are found beneath the ocean floor.

3. Importance of Oceans
Approximately one-third of the world’s table salt is extracted from seawater through the process of evaporation.
Oceans also allow for the efficient transportation of goods. For example, millions of tons of oil, coal, and grains are shipped over the oceans each year.

4. Oceanography – study of Earth’s oceans

5. SONaR – sound navigation and ranging
Uses return time of an echo and the known velocity of sound in water to determine water depth
Side-scan Sonar – sound waves hit floor at an angle so features are mapped
Has mapped large portions of the seafloor

7. Origins of Water
Scientists hypothesize that Earth’s water could have originated from two sources
Comets and meteorites colliding with the planet
Impacts release water, possibly enough to fill the ocean basins over geologic time
Volcanoes – emit significant quantities of gas, mostly water vapor and carbon dioxide
Earth cooled and water vapor condensed into oceans

8. Distribution of Earth’s Water
97% of water in oceans, 3% of water is fresh
The percentage of ice on Earth has varied over geologic time from near zero to as much as 10% of the hydrosphere
Global sea level has risen and fallen by hundreds of meters in response to melting and freezing ice
Tectonic forces that lift or lower portions of the seafloor

9. The Blue Planet 71% of Earth’s surface is covered by oceans
Average depth of an ocean is 3800 meters
All the oceans are really one vast, interconnected body of water
Divided into specific oceans and seas because of historic and geographic considerations

10. Major Oceans Pacific Ocean Atlantic Arctic Indian
Largest – contains roughly half of Earth’s seawater
Atlantic
2nd largest – extends from Antarctica to the arctic circle
Arctic
Atlantic Ocean north of the arctic circle
Indian
Located mainly in the southern hemisphere

11. Minor Oceans Antarctic Storm-lashed region surrounding Antarctica
South of 50 degrees south latitude
Sometimes referred to as the Southern Ocean

12. Seas Seas are smaller than oceans and are partly or mostly landlocked
3 major seas are
Mediterranean
Caribbean
Bering

13. 15.2 Seawater

14. Seawater
Seawater is a solution of about 96.5% water and 3.5% dissolved salts.
Most abundant salt in seawater is sodium chloride (NaCl)
Other salts present are chlorides and sulfates of magnesium, potassium, and calcium
Salinity is the measure of the amount of dissolved salts in seawater

16. Variations in Salinity
Average salinity of the oceans is 35 ppt (parts per thousand)
Salinities higher in subtropics due to higher rates of evaporation
In equatorial regions salinities are lower due to abundant precipitation
Polar regions low due to melting sea ice
Lowest salinities occur where large rivers empty into the ocean

18. Sources of Sea Salt
Ancient seas salinity not much different from today
Volcanic gases contain chlorine and sulfur dioxide
Gases dissolve in water and form the chlorine and sulfate ions of seawater
Weathering of crustal rocks generates most of the other abundant ions in seawater
Sodium, calcium, potassium, iron, magnesium

19. Removal of Sea Salts Salinity in ocean never really increases
Removal involves several processes
Some precipitate from seawater near arid, coastal regions
Small salty spray droplets from breaking waves are picked up by winds and deposited inland
Marine organisms also remove ions from seawater to build their shells, bones, and teeth

21. Physical Properties of Seawater
Physical properties of seawater are quite different than freshwater
Salt ions are heavier than water molecules and increase the density
The freezing point of seawater -2 degrees C
Determining factors for temperature are
Depth
Latitude
Salinity

22. Temperature Average Sea-Surface Temperature (SST) = 26 C Zones
Ocean water temperatures decrease significantly with depth
Zones
Surface
0-100 meters
Little to no temperature change

23. Thermocline (intermediate)
Rapid decrease in temperature
Bottom
Below 1000 m
Temperature levels out and becomes stable because of pressure

24. Absorption of Light Light intensity decreases with depth
Water absorbs light
Penetrates only the upper 100m of seawater
Photosynthesis will only occur in this first 100 m
Some blue light reaches below that, but is not used for photosynthesis

25. Light Zones Sunlit Zone – Euphotic Zone Twilight Zone – Disphotic Zoneft
>90% of marine animals live here
Twilight Zone – Disphotic Zone
About 900 ft
Midnight Zone – Aphotic Zone
Below 900 ft

26. Other Zones Littoral Zone Neritic Pelagic Benthic Between tide lines
Low tide line to the edge of the continental shelf
Pelagic
Open ocean
Benthic
Bottom of open ocean

27. 15.3 Ocean Movements

28. Oceans are never completely motionless
Most obvious movement is the constant motion of the waves
Rhythmic movement that carries energy through space or matter
Water moves up and down in a circular pattern and returns to its original position

29. Waves Typical wave characteristics Crest – highest point of a wave
Trough – lowest point of a wave
Wave height – distance between crest & trough
Wave length – distance from crest to crest

30. Wave Height Depends on 3 things Wind speed Wind duration(how long)
Fetch (how much distance wind blows across)

31. Breaking Waves
As ocean waves reach the shallow water near shorelines, they lose energy because of friction with the ocean bottom
Waves slow down
Incoming waves become higher, steeper, and unstable, and their crests collapse forward
Breakers – waves where the crest collapse