1. Music today: Billy Ocean, “Get Outta My Dreams and Into My Car”
Available by Wednesday: Find your Midterm Exam score at the class web site, under “Lectures”, April 26
Scantrons and Short Answers will be returned at Labs next week

2. The Properties of Sea Water
What makes water so special?
Why is the ocean salty?

3. Where’s the Water?
Reservoir Volume (106 km3) Percent Ocean Ice (polar) Groundwater Lakes Atmosphere Rivers

4. Where did the water in the Oceans come from?
Outgassing (H2O, CO2) of the Earth from volcanoes, early in its history
Sedimentary rocks as old as 3.8 billion years!
A much smaller amount from comets that pass by

5. The Water Molecule

6. Water is a “Polar” Molecule
Weak electrical attraction makes for “sticky” molecules
This explains its unique properties: heat capacity surface tension dissolving power

7. Temperature vs Heat
Temperature is a measure of how fast the molecules in a substance are moving
Heat is a measure of how much energy has to be put into (or gotten out of) a substance to change its temperature, or “state” (solid, liquid, gas)

8. Sensible Heat vs Latent Heat
Sensible heat is what we sense from different temperatures
Latent heat is the energy needed to change state (ice to water, water to vapor)

9. Table 4.2 (6th edition)

10. Exists in three states on the planet surface
water vapor
ice
liquid water

11. Water co-exists on the Earth in 3 physical states:
Changes of state
Water co-exists on the Earth in 3 physical states:
solid
liquid
gas

12. Changes of state always occur at constant temperature
The heat needed for a change of state is called latent heat

13. Heat and the three Physical States of Water:

14. But it requires more energy to do so
Evaporation from lakes, oceans, rivers, etc. occurs for temperatures lower than 100 oC
But it requires more energy to do so

15. Density of Pure Water

16. Consequences…

17. Consequences Bottom temperature of deep, cold lakes is always 4 oC.
Pipes (or beer bottles) freeze and burst.
Ice floats on the water surface

18. Water has the highest surface tension of all common liquids
Surface tension - measure of how difficult it is to stretch or break the surface of a liquid
Water has the highest surface tension of all common liquids

19. Major source of energy to power the Earth’s weather systems
Energy liberated into the atmosphere (condensation)
Energy removed from surface (evaporation)

20. Special Properties of Water
Density of solid is less than liquid
Melting and boiling points are very high
Highest heat capacity
High heat of fusion and vaporization
Tremendous dissolving power

21. Dissolving Power of Water

22. Why is the Ocean Salty? Total dissolved solids (called “salinity”)
About 3.5% by weight (average seawater)
Usually expressed as 35 0/00 (parts per thousand, ppt)
Varies geographically according to Evaporation, Precipitation, and Rivers

23. The Most Abundant Ions Chloride (Cl-) 19.0 g/kg Sodium (Na+) 10.6 “
Sulfate (SO42-) “
Magnesium (Mg2+) “
Calcium (Ca2+) “
Potassium (K+) “ g/kg

24. Ions in Sea Water Anions are negatively charged Cl-, SO4-
Cations are positively charged Na+, K+, Ca++, Mg++

25. Measuring Salinity
Principle of Constant Proportions e.g., SO42-/Cl- is a constant, independent of salinity
This means we need measure only one ion to get salinity; i.e., Cl-
Today salinity is measured quickly by electrical conductivity of sea water

26. Where does Salinity come from?
Terrigenous input (rivers, dust, ash)
Hydrothermal vents
Dissolving old sediments (evaporites)
Steady State: Inputs equal Outputs

27. Weathering of Rocks H2O + CO2 ---> H2CO3 (carbonic acid)
“acid” rain, pH ~4-5; environmental concerns (HCl, HF, H2SO4)
Dissolves rock minerals into ions, which travel down rivers to the ocean

28. Residence Time
How long do the various dissolved ions stay in the ocean? Depends on how “reactive”.
Residence Time: The average time spent by a substance in the Ocean = Amount in Sea Rate entering or exiting

29. Residence Time
For water entering through rivers, the residence time is about Volume = 1370x106 km3 (oceans) Flux x106 km3/yr (rivers) = 35,000 years. For Cl-, the residence time is 100 Ma! For Fe2+, the residence time is 200 yr Which is likely to obey Constant Proportions?

30. Adding salt lowers the freezing temperature:
Seawater freezes at about -2 oC
Freezing removes fresh water, leaves salt

31. The Hydrologic Cycle

32. Evaporation - Precipitation
Over the oceans, evaporation exceeds precipitation
The balance is restored by rain over the continents, returning water via rivers

33. Desalination -- fresh water from the Oceans

34. Salt in the Ocean and its relationship to density
Average ocean salinity 35 per mil
1000 g of seawater = 965 g of water + 35 g salt
If all of the water in the oceans evaporated, this amount of salt would form a layer roughly 45 m thick over the entire surface of the Earth

35. Ocean Surface salinities

36. Evaporation vs Precipitation

37. Which processes change the
surface salinities ?
saltier
fresher
 evaporation
 precipitation
 sea ice formation
 sea ice melting
 freshwater runoff from land

38. Which ocean is the saltiest?

39. Which ocean is Saltiest?
In spite of the fact that many more big rivers empty into the Atlantic than the Pacific, the Atlantic is actually significantly saltier because of the evaporation-precipitation cycle and the Isthmus of Panama; the Indian is intermediate

40. Surface salinities Evaporation, precipitation, and wind patterns
explain high/low salinity of Atlantic/Pacific.

41. Summary:
Water is a polar molecule -- unique properties (melting pt, heat capacity, dissolving power, water denser than ice)
Salinity is the total dissolved solids
Salinity in the surface ocean varies by Evaporation - Precipitation
Principle of Constant Proportions
Residence Time in the Oceans