1. Chapter 6: Water and Seawater Fig. 6-19

2. Atomic structure Nucleus Protons and neutrons Electrons Ions are charged atoms

3. Water molecule H 2 O Two hydrogen, one oxygen Bonded by sharing electrons Bend in geometry creates polarity Dipolar molecule

5. Weak negative charge at O end Weak positive charge at H end Hydrogen bonds Weak bonds between water molecules and ions Explains unusual properties of water

6. Fig. 6-3

7. Two unusual properties High surface tension Hydrogen bonding creates “skin” Important for living organisms Capillarity Universal solvent Electrostatic bond between dipolar water and ions Ocean is salty

8. Fig. 6.4

9. Fig. 6-5b

10. Thermal properties of water Solid, liquid, gas on Earth’s surface Water has high freezing point Water has high boiling point Water has high heat capacity Water has high latent heats

11. Fig. 6-7

12. Heat capacity Heat absorbed or released with changes in state Latent heats of Melting; freezing Vaporization, evaporation Condensation

13. Global thermostatic effects Moderate global temperature Evaporation removes heat from oceans Condensation adds heat to atmosphere Heat re-distributed globally

14. Differences in day and night temperatures

15. Water density Maximum density at 4 o C Ice less dense than liquid water Atomic structure of ice Ice floats Increased salinity decreases temperature of maximum density

16. Fig. 6-10

17. Fig. 6-8

18. Seawater Salinity=total amount of solid material dissolved in water (g/1000g) Typical salinity is 35 o/oo or ppt Brackish (hyposaline) < 33 ppt Hypersaline > 38 ppt

20. Measuring salinity Evaporation Chemical analysis Principle of Constant Proportions Chlorinity Electrical conductivity (salinometer)

21. Dissolved substances Added to oceans River input (primarily) Circulation through mid-ocean ridges Removed from oceans Salt spray Recycling through mid-ocean ridges Biogenic sediments (hard parts and fecal pellets) Evaporites

22. Residence time Average length of time a substance remains dissolved in seawater Long residence time = unreactive Higher concentration in seawater Short residence time = reactive Smaller concentration in seawater Steady state Ocean salinity nearly constant through time

23. Dissolved gases Solubility depends on temperature, pressure, and ability of gas to escape Gases diffuse from atmosphere to ocean Wave agitation increases amount of gas Cooler seawater holds more gas Deeper seawater holds more gas

24. Conservative vs. nonconservative constituents Conservative constituents change slowly through time Major ions in seawater Nonconservative constituents change quickly due to biological and chemical processes Gases in seawater

25. Oxygen and carbon dioxide in seawater Nonconservative O 2 high in surface ocean due to photosynthesis O 2 low below photic zone because of decomposition O 2 high in deep ocean because source is polar (very cold) ocean

26. CO 2 low in surface ocean due to photosynthesis CO 2 higher below photic zone because of decomposition Deeper seawater high CO 2 due to source region and decomposition

27. Acidity and alkalinity Acid releases H+ when dissolved in water Alkaline (or base) releases OH- pH scale measures acidity/alkalinity Low pH value, acid High pH value, alkaline (basic) pH 7 = neutral

28. Carbonate buffering Keeps ocean pH about same (8.1) pH too high, carbonic acid releases H+ pH too low, bicarbonate combines with H+ Precipitation/dissolution of calcium carbonate CaCO 3 buffers ocean pH Oceans can absorb CO 2 from atmosphere without much change in pH

29. Fig. 6-17

30. How salinity changes Salinity changes by adding or removing water Salinity decreases by Precipitation (rain/snow) River runoff Melting snow

31. Salinity increases by Evaporation Formation of sea ice Hydrologic cycle describes recycling of water

32. Hydrologic cycle Fig. 6-19

33. Horizontal variations of salinity Polar regions: salinity is lower, lots of rain/snow and runoff Mid-latitudes: salinity is high, high rate of evaporation Equator: salinity is lower, lots of rain Thus, salinity at surface varies primarily with latitude

34. Fig. 6-20

35. Vertical variations of salinity Surface ocean salinity is variable Deeper ocean salinity is nearly the same (polar source regions for deeper ocean water) Halocline, rapid change of salinity with depth

37. Density of seawater 1.022 to 1.030 g/cm 3 Ocean layered according to density Density of seawater controlled by temperature, salinity, and pressure Most important influence is temperature Density increases with decreasing temperature

38. Salinity greatest influence on density in polar oceans Pycnocline, rapid change of density with depth Thermocline, rapid change of temperature with depth Polar ocean is isothermal

40. Layers of ocean Mixed surface layer Pycnocline Deep ocean

41. End of Chapter 6: Water and Seawater