1. Section 2: Seawater
Oceans have distinct layers of water masses that are characterized by temperature and salinity. K
What I Know W
What I Want to Find Out L
What I Learned

2. Essential Questions What is the composition of seawater?
What are the physical properties of seawater?
How is ocean layering illustrated?
How do deepwater masses form?
Seawater
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3. Vocabulary Review New feldspar salinity estuary temperature profile
thermocline
Seawater
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4. Chemical Properties of Seawater
Ocean water contains dissolved gases, including oxygen and carbon dioxide, and dissolved nutrients such as nitrates and phosphates.
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Seawater

5. Chemical Properties of Seawater
Levels of dissolved gases and nutrients in seawater vary by location and depth.
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Seawater

6. Chemical Properties of Seawater
Salinity
The measure of the amount of dissolved salts in seawater is salinity.
Oceanographers express salinity as grams of salt per kilogram of water, or parts per thousand (ppt).
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7. Chemical Properties of Seawater
Variations in salinity
Although the average salinity of the oceans is 35 ppt, actual salinity varies from place to place.
Seawater
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8. Chemical Properties of Seawater
Variations in salinity
The lowest salinity often occurs where large rivers empty into the oceans, creating areas of water called estuaries.
Even though salinity varies, the relative proportion of major types of sea salts is constant because all ocean water continually intermingles throughout Earth’s oceans.
Seawater
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9. Chemical Properties of Seawater
Sources of sea salt
Geologic evidence indicates that the salinity of ancient seas was not much different from that of today’s oceans.
Sources of sea salts have also stayed the same over time.
Seawater
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10. Chemical Properties of Seawater
Sources of sea salt
Sulfur dioxide and chlorine, gases released by volcanoes, dissolve in water, forming sulfate and chlorine ions.
Most of the other ions in seawater, including sodium and calcium, come from the weathering of crustal rocks, such as feldspars.
Iron and magnesium come from the weathering of rocks rich in these elements. These ions enter rivers and are transported to oceans.
Seawater
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11. Visualizing the Salt Cycle
Salts are added to seawater by volcanic eruptions and by the weathering and erosion of rocks. Salts are removed from seawater by biological processes and the formation of evaporites. Also, wind carries salty droplets inland.
Seawater
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12. Add link to Animation from p. 415 here.
Visualizing the Salt Cycle
Concepts In Motion
FPO
Add link to Animation from p. 415 here.
Seawater
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13. Chemical Properties of Seawater
Removal of sea salt
In arid coastal regions, water evaporates from seawater and leaves solid salt behind.
Marine organisms remove ions from seawater to build shells, bones, and teeth.
Seawater
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14. Chemical Properties of Seawater
Removal of sea salt
Winds can pick up salty droplets from breaking waves and deposit the salt further inland.
The existing salinity of seawater represents a balance between the processes that remove salts and those that add them.
Seawater
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15. Add link to Interactive Table from p. 416 here.
Removal of Sea Salts
Concepts In Motion
FPO
Add link to Interactive Table from p. 416 here.
Seawater
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16. Physical Properties of Seawater
Density
Because salt ions add to the overall mass of the water in which they are dissolved, they increase the density of water. Seawater is therefore more dense than freshwater, and its density increases with salinity.
Seawater
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17. Physical Properties of Seawater
Density
Temperature also affects density—cold water is more dense than warm water.
Because of salinity and temperature variations, the density of seawater ranges from about 1.02 g/cm3 to 1.03 g/cm3.
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18. Physical Properties of Seawater
Freezing point
Variations in salinity also cause the freezing point of seawater (–2°C) to be somewhat lower than that of freshwater (0°C).
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19. Physical Properties of Seawater
Absorption of light
Water absorbs light, which gives rise to another physical property of oceans—darkness.
In general, light penetrates only the upper 100 m of seawater.
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20. Ocean Layering Temperature profiles
This figure shows typical ocean temperature profiles, which plot changing water temperatures against depth. Such profiles vary, depending on location and season.
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21. Ocean Layering Temperature profiles
In general, ocean layering is caused by density differences. Because cold water is more dense than warm water, cold water sinks to the bottom, while less-dense, warm water is found near the ocean’s surface.
Seawater
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22. Ocean Layering Temperature profiles
The thermocline is the transitional ocean layer that lies between the relatively warm, sunlit surface layer and the colder, dark, dense bottom layer. It is characterized by temperatures that decrease rapidly with depth.
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23. Water Masses Deepwater masses
Dense polar water sinks, producing a deepwater mass.
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24. Water Masses Deepwater masses
Three water masses account for most of the deepwater masses in the oceans—Antarctic Bottom Water, North Atlantic Deep Water, and Antarctic Intermediate Water.
Seawater
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25. Water Masses Deepwater masses
Antarctic Bottom Water is the densest and coldest deepwater mass. It is overridden by the slightly warmer and less dense North Atlantic Deep Water.
Seawater
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26. Water Masses Intermediate water masses
Antarctic Intermediate Water is warmer and less dense, and thus it overrides the other two deepwater masses.
Seawater
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27. Review Essential Questions Vocabulary
What is the composition of seawater?
What are the physical properties of seawater?
How is ocean layering illustrated?
How do deepwater masses form?
Vocabulary
salinity
estuary
temperature profile
thermocline
Seawater
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