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Chapter 5 Water and Seawater

Chapter 5 Water and Seawater. Essentials of Oceanography 7 th Edition. Atomic structure. Atoms are the building blocks of all matter Nucleus contains: Neutrons (no charge) Protons (+ charge) Outer shell(s) contain: Electrons ( – charge). Figure 5-1. The water molecule.

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Chapter 5 Water and Seawater

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  1. Chapter 5 Water and Seawater Essentials of Oceanography 7th Edition

  2. Atomic structure • Atoms are the building blocks of all matter • Nucleus contains: • Neutrons (no charge) • Protons (+ charge) • Outer shell(s) contain: • Electrons (– charge) Figure 5-1

  3. The water molecule • Composed of 1 oxygen and 2 hydrogen atoms (H20) • Contains strong (covalent) bonds between atoms • Unusual bend in geometry • Has polarity (oppositely charged ends) Figure 5-2a

  4. Interconnections of water molecules • Polarity causes water molecules to form weak (hydrogen) bonds between water molecules • Water sticks to itself and to other substances • Allows water to be the universal solvent Figure 5-3

  5. Water as a solvent • Water dissolves table salt (NaCl) by attracting oppositely charged particles • Pulls particles out of NaCl structure to dissolve it Figure 5-4

  6. Water in the 3 states of matter • Latent (hidden) heat = energy that is either absorbed or released as water changes state Figure 5-5

  7. The ocean moderates coastal temperatures • Water has high heat capacity, so it can absorb (or release) large quantities of heat without changing temperature • Moderates coastal temperatures Figure 5-6

  8. Hydrogen bonds in H2O Figure 5-8

  9. The formation of ice • As water cools to 4°C: • Molecules slow • Water contracts • Density increases • Below 4°C: • Hydrogen bonds form • Water expands • As water freezes: • Expands by 9% Figure 5-11

  10. Snowflake geometry • All snowflakes have 6-sided geometry • Caused by water’s polarity and ability to form hydrogen bonds Figure 5-12

  11. Salinity • Salinity = total amount of solid material dissolved in water • Can be determined by measuring water conductivity • Typically expressed in parts per thousand (‰) Figure 5-15

  12. Constituents of ocean salinity • Average seawater salinity = 35‰ • Main constituents of ocean salinity: • Chloride (Cl–) • Sodium (Na+) • Sulfate (SO42–) • Magnesium (Mg2+) Figure 5-13

  13. Salinity variations

  14. Ocean buffering • Ocean pH = 8.1 (slightly basic) • Buffering protects the ocean from experiencing large pH changes Figure 5-18

  15. Processes affecting seawater salinity • Processes that decrease seawater salinity: • Precipitation • Runoff • Icebergs melting • Sea ice melting • Processes that increase seawater salinity: • Sea ice forming • Evaporation

  16. The hydrologic cycle Figure 5-19

  17. Surface salinity variation • Pattern of surface salinity: • Lowest in high latitudes • Highest in the tropics • Dips at the Equator • Surface processes help explain pattern Figure 5-20

  18. Surface salinity variation • High latitudes have low surface salinity • High precipitation and runoff • Low evaporation • Tropics have high surface salinity • High evaporation • Low precipitation • Equator has a dip in surface salinity • High precipitation partially offsets high evaporation

  19. Global surface salinity Figure 5-21

  20. Salinity variation with depth • Curves for high and low latitudes begin at different surface salinities • Halocline = layer of rapidly changing salinity • At depth, salinity is uniform Figure 5-22

  21. Seawater density • Factors affecting seawater density: • Temperature ↑, Density ↓ (inverse relationship) • Salinity ↑, Density ↑ • Pressure ↑, Density ↑ • Temperature has the greatest influence on surface seawater density

  22. Density and temperature variations with depth Figure 5-24

  23. Pycnocline and thermocline • Pycnocline = layer of rapidly changing density • Thermocline = layer of rapidly changing temperature • Present only in low latitude regions • Barrier to vertical mixing of water and migration of marine life

  24. Ocean layering based on density • Mixed surface layer (surface to 300 meters) • Low density; well mixed by waves, currents, tides • Upper water (300 to 1000 meters) • Intermediate density water containing thermocline, pycnocline, and halocline (if present) • Deep water (below 1000 meters) • Cold, high density water involved in deep current movement

  25. Seawater desalination • Desalination methods: • Distillation • Solar • Heat • Electrolysis • Reverse osmosis • Freeze separation Distillation Figure 5-25 Reverse Osmosis Figure 5-26

  26. End of Chapter 5 Essentials of Oceanography 7th Edition

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