Ocean, water and Seawater Oceanography

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