Water and ocean structure

1
Lecture 5
Water and ocean structure
22 August 2007
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Lecture schedule
Lecture Date Time 1. Introduction to
scientific writing 8/20 900-1020 2. How to
write a scientific paper in English 8/20 1500-16
20 3. Earth structure and plate
tectonics 8/21 900-1100 4. Circulation of the
atmosphere 8/21 1300-1500 5. Water and ocean
structure 8/22 1000-1100 6. Continental
margins and ocean basins 8/22 1300-1500 7.
Sediment 8/23 1000-1200 8. Marine
resources 8/23 1300-1400 9. Circulation of
the ocean 8/24 1100-1230
3
The water molecule is held together by chemical
bonds

• Atom
• the smallest particle of an element that
  exhibits the characteristics of that element

electrons
(-)
helium atom
neutrons
(no charge)
protons
()
4

• Element
• a substance composed of identical atoms
• cannot be broken into simpler substances by
  chemical means

http//en.wikipedia.org/wiki/ImagePeriodic_table.
svg
5
The water molecule is held together by chemical
bonds

• Atom
• the smallest particle of an element that
  exhibits the characteristics of that element

• Element
• a substance composed of identical atoms
• cannot be broken into simpler substances by
  chemical means

• Molecule
• gt 2 atoms held together by chemical bonds
• examples oxygen (O2)
• water (H2O)

6

• Chemical bonds
• form when atoms share electrons

2 hydrogen atoms
1 oxygen atom
1 water molecule
H2O

covalent bonds
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Examples of covalent bonds
carbon dioxide CO2
methane gas CH4
atmospheric oxygen O2
http//www.its.caltech.edu/atobias/o2molecule.gif
http//www.nyu.edu/pages/mathmol/textbook/oxygen.g
if
8
Because of the way the water molecules oxygen
atoms are distributed, the shape of the molecule
is bent
Electrically asymmetric
_

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attracts
-

• behaves like a magnet
• called a polar molecule

-
attracts

Hydrogen bond

• about 5-10 as strong as a covalent bond
• allow water molecules to stick to each other

cohesion
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Cohesion gives water a high surface tension
Hydrogen bonds make this possible
water strider
http//content.answers.com/main/content/wp/en-comm
ons/thumb/6/6b/250px-Wasserläufer_bei_der_Paarung_
crop.jpg
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What would happen if there were no hydrogen bonds?
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What would happen if there were no hydrogen bonds?
At normal temperatures and pressure, H20 would
form a gas rather than a liquid
hydrogen sulfide (H2S)
http//www.uwosh.edu/faculty_staff/xie/molecules/h
2s-2.gif
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Question Time!

• What holds molecules together?

14
Question Time!

• What holds molecules together?
• 2.Why is water a polar molecule?

15
Water has unusual thermal characteristics

• heat energy produced by the random vibration of
  atoms/molecules
• measured by
• how many molecules are vibrating
• how rapidly they are vibrating

heat

• temperature

• measured in degrees

16

• Temperature
• a number related to the average kinetic energy
  of the molecules of a substance

• Heat
• a measurement of the total energy in a substance
  
• kinetic energy potential energy

17
Bathtub of hot water
Candle
Which one has

• higher temperature?

• more heat?

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Bathtub of hot water
Candle
Which one has
?

• higher temperature?

Molecules vibrate very rapidly, but very few

• more heat?

19
Bathtub of hot water
Candle
Which one has
?

• higher temperature?

Molecules vibrate very rapidly, but very few
?

• more heat?

Molecules vibrate more slowly, but there are many
of them
20
Heat capacity

• the heat (measured in calories) required to
  raise 1 gram of a substance 1o Celsius
• different substances have different heat
  capacities

very high

• due to large of hydrogen bonds

water can absorb (or release) large amounts of
heat while changing very little in temperature
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heat capacity
water high sand low
22
heat capacity
water high sand low
23
Waters temperature affects its density.
Where is the warmest water in a tub ?

• at the surface
• cold water tends to sink

But, where does ice form in a lake?
at the surface
http//www-personal.umich.edu/jensenl/visuals/alb
um/2006/ice/IMG_8011.JPG
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Density curve shows the relationship between
temperature (or salinity) and density
4oC
Ice is less dense than liquid water and thus
floats because the molecules are packed less
efficiently.
freezing point
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water
ice
angle 109o
angle 104o
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The three states of water
to melt
to evaporate
gas (water vapor)
liquid
solid (ice)
to freeze
to condense
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gas
liquid
solid
Temperature
lt0oC
gt100oC
0-100oC
Molecular movement
fast
fastest
slow
Density
low
highest
lowest
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When heat goes into a substance, one of two
things can happen

• rise in temperature
• increased kinetic energy

energy
or
substance

• change in state
• increased potential energy

29
States of water
to melt
to evaporate
gas (water vapor)
liquid
solid (ice)
to freeze
to condense

• very high
• all hydrogen bonds must be broken

The term latent applies to heat input that does
not cause a temperature change but does produce a
change of state.
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Summary
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Question Time!
How is heat different from temperature?
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Surface water moderates global temperature
The tendency of a substance to resist a change in
temperature with the gain or loss of heat energy
is called thermal inertia.
Low thermal inertia
High thermal inertia
Range -2o 32o -90o 50o
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Heat
No change
No change
Temperature
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Norfolk
Wind direction
San Francisco
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Annual freezing and thawing of ice moderate
Earths temperature
adds 80 calories of heat energy/g liquid water
solid (ice)
liquid
removes 80 calories of heat energy/g liquid water

• gt18,000 km3 of polar ice thaws and refreezes in
  the Southern Hemisphere each year
• in summer, ice melts, but ocean temperature does
  not change
• in winter, water freezes, but ocean temperature
  does not change

Seasonal extremes are moderated.
36
Movement of water vapor from tropics to poles
also moderates Earths temperature

• poleward transfer of heat
• 2/3 by air
• 1/3 by ocean currents

37
Global warming may be influencing ocean-surface
temperature and salinity
S
N

• tropical ocean lt 1000 meters is becoming warmer
  and saltier
• water in the far north and south has become
  fresher

38
Ocean-surface conditions depend on latitude,
temperature, and salinity
Evaporation gt precipitation
Precipitation gt evaporation
Evaporation gt precipitation
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Sea surface temperature
Sea surface salinity
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The ocean is stratified by density.
Freshwater density 1.000 g/cm3 Seawater
density 1.020-1.030 g/cm3

• Seawater density is a function of
• temperature
• salinity
• pressure

most important
cold, salty water
warm, less salty water
is more dense than
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The ocean is stratified into three density zones
by temperature and salinity

• Surface zone
• (mixed layer)
• 0-150/1000 m

Pycnocline
Deep zone
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Pycnocline zone in which density increases with
increasing depth.
http//epswww.unm.edu/facstaff/zsharp/103/lecture
2015-16,20oceans20I_files/image010.gif
The pycnocline is a combination of the
thermocline and halocline.
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Thermocline in the Central Pacific
http//svs.gsfc.nasa.gov/vis/a000000/a000200/a0002
80/thermo_actual_9706.jpg
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Thermocline in Lake Biwa, Japan
http//www.lbri.go.jp/biwakoview/english/nb/image/
02.gif
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The thermocline form varies with latitude.
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The thermocline form varies seasonally.


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A water mass is a body of water with
characteristic temperature and salinity, and
therefore density.
These layers are distinct water masses
Density stratification usually prevents vertical
water movement.
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Refraction can bend the paths of light and sound
through water
Why does it bend?
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Refraction can bend the paths of light and sound
through water
Why does it bend?
Due to a difference in density
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(No Transcript)
51
Light in the ocean
Visible light is only a small part of the
electromagnetic spectrum
http//www.astro.virginia.edu/class/skrutskie/imag
es/light_em_spectrum.jpg
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• It is difficult for sunlight to penetrate the
  ocean.
• clouds and the sea surface reflect light
• gasses and particles scatter and absorb light

scattering
photic zone sunlit surface of the ocean
Open ocean 100-600 m Coastal water 40 m
aphotic zone
http//hydram.epfl.ch/VICAIRE/mod_2/chapt_12/pictu
res/fi26.jpg
absorption
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The energy of some colors of light is absorbed
near the surface more than other colors are.
The top meter of ocean absorbs 71 of red light.
Water transmits blue light more efficiently than
red light.
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http//oceanexplorer.noaa.gov/explorations/04deeps
cope/background/deeplight/media/diagram3.html
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Why is the ocean blue?

• because blue light can travel through water far
  enough to be scattered back to our eyes

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What does red look like underwater?
At 0 m depth
At 10 m depth
Colors as seen underwater (no strobe light)
Actual colors (with strobe light
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As a result, many deep-sea animals are red  
Deep-sea spider crab    
Deep-sea shrimp    
http//oceanexplorer.noaa.gov/explorations/islands
01/islands01.htmlhttp//www.oceanexplorer.noaa.gov
/explorations/04alaska/logs/aug20/media/spider_cra
b_600.jpg
http//www.divediscover.whoi.edu/expedition5/daily
/ss010905/4.jpg
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Sound travels much farther than light in the ocean
Many animals use sound rather than light to see
in the ocean
http//staff.more.net/denise/whales/Echolocation.G
IF
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Speed of sound in air 344 m/sec Speed of
sound in seawater 1,500 m/sec

• Speed of sound in seawater increases
• with temperature, and
• with pressure

60
http//www.pmel.noaa.gov/vents/acoustics/tutorial/
11-sofar.html
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• 1,200 meters in North Atlantic
• 600 meters in North Pacific

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Refraction causes sofar layers and shadow zones
Sofar layer
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Refraction causes sofar layers and shadow zones
Sofar layer
loud noises made at this depth can be heard for
1000s of kilometers

• Sound waves do not propagate straight in the
  ocean
• tend to bend towards layers of lower sound
  velocity

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Shadow zones
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http//ioc.unesco.org/oceanteacher/oceanteacher2/o
ther/Intro2PhysOc/IntroOc/notes/figures/images/fig
5a4.gif
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Sonar systems use sound to detect underwater
objects
Active sonar the projection and return through
water of short pulses of sound to search for
objects in the ocean
http//www.solcomhouse.com/lfa.jpg
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One of the most useful types of active sonar is
side-scan sonar

• Used in
• geological investigations
• archaeological investigations
• locating downed ships and airplanes

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side-scan sonar
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Side-scan sonar image of the SS Nailsea
Meadow depth 113 m
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Key Points
1. The water molecule is held together by
chemical bonds. 2. Water has unusual thermal
characteristics. 3. Surface water moderates
global temperature.  4. Annual freezing and
thawing of ice moderate Earths temperature. 5.
The ocean is stratified by density.  6.
Refraction can bend the paths of light and sound
through water.  7. Light does not travel far
through the ocean. 8. Sound travels much farther
than light in the ocean.
71
Lecture schedule
Lecture Date Time 1. Introduction to
scientific writing 8/20 900-1020 2. How to
write a scientific paper in English 8/20 1500-16
20 3. Earth structure and plate
tectonics 8/21 900-1100 4. Circulation of the
atmosphere 8/21 1300-1500 5. Water and ocean
structure 8/22 1000-1100 6. Continental
margins and ocean basins 8/22 1300-1500 7.
Sediment 8/23 1000-1200 8. Marine
resources 8/23 1300-1400 9. Circulation of
the ocean 8/24 1100-1230