1. Water - the Earth’s Coolant
Chapter 23 and 24

2. Put this in your notes: The Earth’s energy is solar. Incident light
from the Sun heats the surface. Water’s
high heat capacity allows it to absorb or
give up this energy without much
temperature change. Circulation in the
ocean and atmosphere redirects energy from
regions of excess (tropical zones to regions
of deficit (polar zones), moderating
temperatures in both.

3. + - Now, let’s explain this process!
Water is the Mickey Mouse molecule:
the covalent bond between O,H tends to pull the electron
from H towards the O and push some of O’s electrons
away from the H’s. - + H O
hydrogen has one proton(+) and one electron (-)
oxygen has 8 protons and 8 electrons

4. + - H O Water is a polar molecule (one end is
more negative and the other is more
positive).

5. Why do you think the polar nature
Why should I care??!!
H and O from different
molecules form weak
bonds (hydrogen bonds)
that make water a liquid.
Why do you think the polar nature
allows this to happen?

6. The polar nature of water also makes
it a VERY good dissolver (THINK:
what do you do with a really yucky
pan- soak it overnight!)
This polar nature also makes water wet-
it adheres (sticks) well to things

7. What else can we blame on water’s polar nature?…..
Water’s ability to absorb heat energy
without a big rise in temperature!
…or give up heat without a big
drop in temperature)
Let’s look at heat and temperature:
(… there is a difference, you know!)

8. Heat is the energy of molecular vibration.
Temperature is a measure of that energy.
Solids have low enough energy that
molecules can form rigid bonds.
Gases have such high energies that
the molecules cannot form bonds.
Transitions between states take place by adding or removing energy.

9. Heat capacity is how much heat one gram
of a material can absorb before its
temperature changes by 1°C.
Water has one of the highest heat
capacities of any known substance.
This is because the hydrogen bonds in liquid water
are strong enough that lots of heat (vibrational)
energy is required to break these bonds, (and
remember, the hydrogen bonds are a consequence
of the polar nature of water.

10. This is why beaches are HOT
and the surf is COOL!
AHH!
Cool water!
OUCH!
Hot feet,burn, OUCH!
… even though both get the same solar heat.

11. Which is denser, liquid water or ice?
More weird properties of water….
Which is denser, liquid water or ice?
NO! water is denser,
ice cubes float!
Water is the only substance
with a solid density less
than its liquid.

12. E-D - all ice, adding heat raises temperature of ice to 0°C (melt point)
D-C - ice + liquid water, constant T because all heat going to melt ice
C-F - all liquid, heat raises temperature of water by 1°C for each calorie
added per gram.
F-G - liquid + vapor, water boiling, constant T because heat added goes
to breaking H bonds and allowing molecules to escape (boil)

13. Ice melting gives up almost as much heat
energy (80 calories) as it takes to raise the
temperature of 1 gram of water from freezing
temperature (0) to boiling (100°C).

14. .. and it takes over 5 times as much (540 calories)
heat to boil a gram of water!

15. Note: Fog is NOT water vapor. It is made of tiny droplets
of liquid water that have condensed in the atmosphere from
vapor. This vapor has given up its 540 cal/gram of energy
to form the droplets (warming the air).

16. Why is this important to you?
1. In hot climates, evaporating water
absorbs LOTS of heat energy that could
go to heating you up! (the water in your
perspiration gets some of that energy
from your skin, cooling you). TROPICS
2. In cold climates, freezing water gives up
heat to keep the air from getting any colder
than 0°C. POLAR REGIONS
3. In your cold drink, melting ice absorbs
heat that could go to warming the liquid.
This is why your drink stays cold!

17. But the ocean is NOT pure water. What
is the principal difference between water
and seawater?
It’s SALTY!!
Sea water
contains about
3.5% dissolved
solids and 96.5%
water

18. These salts lower the freezing point
of sea water to ~ -2°C because the
salt interferes with lattice of ice crystals.
(acts as antifreeze!)
This is why we can make ice cream!!
Adding salt to ice lowers the melting
temperature of the mix to -2°C, but
the water in the ice cream mix still
freezes at 0°C. Thus, heat flows from
the mix to the salty ice.

19. Oh, yeah, there are also some important consequences for the ocean…..
When sea water begins
to freeze, the ice that
forms is pure water
and the remaining
liquid is concentrated
in salts. It is denser,
and this cold, salty
water sinks into the
deep ocean. CREATES OCEAN CIRCULATION!

20. The ocean acts as a thermal buffer:
it absorbs or radiates heat in order
to try to keep its temperature constant:
Sahara Desert (50°C) to Antarctic
continent (-90°C) on continents
140 °C
Ocean changes from freezing (-2 °C)
to the tropics (34 °C)
36 °C

21. Why would Norfolk have a much larger
temperature variation than San Francisco?
(same solar input and both next to ocean)
Prevailing Wind Direction
San Francisco has smaller temperature
fluctuation because winds blow air
from ocean and ocean moderates
temperature.
Norfolk has larger
temperature variation
because its air is blown
off the continent.

22. The ocean moderates the Earth’s surface temperature by:
1. transporting heat from the tropics
where there is an excess to the polar
regions where there is a deficit - currents
such as the Gulf Stream
(1/3 from oceans, 2/3 from atmosphere)
2. Melting and freezing polar ice each year
(THINK: which way does the heat
flow in melting and freezing)
3. Evaporation in tropical regions (and
then transport by atmosphere elsewhere)

23. … but not all of the ocean participates in this buffering effect!
Cold, salty water is denser than
warm, less salty water.
What happens?
Dad, dense stuff SINKS!
.. and then, Bart, the cold, salty water rises…
There you go again with gravity!
Why? GRAVITY!!!!

24. The ocean is layered due to density differences caused by:
Sometimes
salinity
Always temp.
Involved in buffering of climate
Surface zone - well mixed. WHY?
Waves, currents
Pyncocline - region of rapid increase in density
Deep zone - stable density, 80% of water
Isolated

25. Movement between layers does not
happen unless density is about the same (WHY?)
Why would
the shallow
temperature in the
polar region be
about the same as
in the deep zone?
Little solar heating!!

26. Variations in sea surface temperature
lead to several climatic phenomena:
The Gulf Stream is the reason
that Europe has such a moderate
climate (compare Canadian
Arctic to England)
Warm sea surface temperatures pushed across
the ocean lead to El Niño conditions.
Shallow temp ~ deep temp, so turbulence creates upwelling
of cold, nutrient-rich water -- HIGH biologic productivity!

27. Salinity variations can be explained by a balance between
evaporation (makes water saltier) and precipitation (makes
water less salty):
P>E
E>P
P>E

28. What else happens in the surface, or
mixed, zone?
LIFE!!
Life requires LIGHT - photosynthesis
is the basis of life for most of the planet.
… but how deep does light go?

29. Photic
zone
Little light penetrates to below photic zone
and it is blue (hydrogen bonds in water
absorb red light)

30. What you photo
with a strobe:
What you see:
(only blue light)

31. The effects of density, temperature,
and salinity layering affects provides
places for submarines to hide….

32. Rule for refraction: sound bends towards low velocity