This document discusses the properties and composition of water and seawater. It explains that water molecules are polar due to hydrogen bonding between oxygen and hydrogen atoms. This polarity allows water to act as a universal solvent and gives it unusual properties like high heat capacity and surface tension. The document also describes seawater, noting that it has an average salinity of 35 parts per thousand and contains dissolved ions from rivers and ocean ridges. Salinity variations in the ocean are driven by evaporation, precipitation, and melting ice.

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

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

3. Water molecule
 H2O
 Two hydrogen, one oxygen
 Bonded by sharing electrons
 Bend in geometry creates polarity
 Dipolar molecule

5. Dipolar molecule
 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 4o
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
 O2 high in surface ocean due to
photosynthesis
 O2 low below photic zone because of
decomposition
 O2 high in deep ocean because source is
polar (very cold) ocean

26.  CO2 low in surface ocean due to
photosynthesis
 CO2 higher below photic zone
because of decomposition
 Deeper seawater high CO2 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 CaCO3 buffers ocean pH
 Oceans can absorb CO2 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/cm3
 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