LECTURE NOTES:
OCEANOGRAPHY (MARSC 100),
SNYDER, L.
CH. 6: Water & Ocean Structure
Wonderful Water: 70% of Earth covered in H2O, 70% of your body is H2O
You die in ~3-5 days without H2O, Regulates Coastal Temperatures
Atoms: smallest units of an element
Atoms made up of smaller particles: Protons (+), Neutrons (no charge), Electrons (-)
Ions: Electrically neutral atoms have the same number of electrons as protons
Ions: atoms with uneven numbers of electrons & protons (electrically charged)
Positive ion: lost an electron (Na+)
Negative ion: gained an electron (Cl-)
Atoms that have more than one shell are most stable w/ 8 electrons in outer shell
Molecules: Atoms bond together to form molecules
Compounds: bonds of different atoms
Covalent bond: Atoms share electrons to become more stable
Water (H2O) has 8 electrons: Polar molecule 105°bend (+ side & - side)
Has 1 oxygen atom w/ 6 electrons (-) & 2 Hydrogen atoms w/ 1 electron each (+)
Water is a Polar Molecule: Having both a (+) & (–) side:
Water acts like an electromagnet
(+) side attracts (–) ions or (–) end of other polar molecules
(–) side attracts (+) ions or (+) end of other polar molecules
Water does this so well, it’s able to dissolve many substances (Universal Solvent)
Hydrogen Bonds: Polar nature of H2O: It’s attracted to other H2O molecules
(+) Hydrogen is attracted to (–) oxygen
Properties of Water:
1. Cohesion: H2O molecules stick together (H+ bonding)
Result: surface tension
2. Adhesion: Attraction of water to other molecules
Result: Capillary action: why your towel gets wet
3. High Heat Capacity: Measure of Heat required to raise the temp. of 1 gram of a
substance by 1°C (1.8°F)
Heat: Energy (kinetic) produced by vibrations of atoms or molecules
Solid water (ice): atoms & water molecules Vibrate weakly, rigidly held in place
Liquid water: Vibrate more rapidly, move freely & farther apart
Gaseous water (vapor): Highly energetic, move far apart
Water resists changing temperature when heat is added or removed
Highest of any liquid or solid (<ammonia)
Hydrogen bonds: a lot of heat must be added to speed up H2O molecule movement &
thus raise its temp.
EX: boil water, Hot sand & cool ocean
Ocean Moderates World Climate: Ocean absorbs a lot of heat w/out changing temp.
Ocean varies in temperature much less than land
Avg. Temp. Ranges: Ocean: –2° to 35°C , Land: –70° to 57°C
4. Water occurs in 3 states: Solid, Liquid, Gas (vapor)
Only substance on Earth (naturally occurring)
Resists changes of state = energy input or removal required
5. High Latent Heat of Fusion: Heat removal required to change water from liquid to
solid (ice)
Freezing Point: Temperature at which a liquid becomes a solid (Water = 0°C)
Why Does Ice Float?
Ice is less dense than water
Density: Mass (wt.) of a substance per unit volume
Number of molecules packed into a volume of space
For most substances,
together): NOT WATER!
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As temp. decreases, H2O molecules vibrate less
At freezing point, packed less efficiently (crystal lattice): result is ice is less dense
than liquid water
Molecules Packed as tight as they will go
Lower temp. & molecules push back harder & Repel each other
Solid water: 24 water molecules, liquid water: 27 water molecules
If ice didn’t float, ocean would become solid ice, no polar bears.
6. High Latent Heat of Vaporization: Heat needed to change water from liquid to gas
Highest of any substance
Energy required to break strong Hydrogen bonds
Water remains a liquid on most of Earth
Ocean Currents help to move water around Earth: Warm water at equator (greater solar
heating), Cold water at poles
Unique Properties of Seawater:
96.5% pure H2O, 3.5% dissolved solids & gases
Presence of solids (salt – NaCl): Lowers the freezing point & Increases density
Density & Stratification:
Seawater can become layered (stratified) b/c of differences in density:
 Surface (2%) Surface: Well mixed (wind, currents), Least dense (Less salty,
Warm)
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Pycnocline (Mid Layer – 18%): Pycnocline: Area of rapidly changing density
(colder, more salty)
Deep Zone
(80%): Deep Zone: Little change in density with increasing depth
(temp. & salinity sabilize)
Pycnocline
Area of rapidly changing:
1. Density
2. Temperature (Thermocline)
3. Salinity (Halocline)
Pycnocline Traps cold, dense salty water at depths
80% of seawater
Deep-water upwelling brings some of this water to the surface
Salinity also varies at the surface of the ocean
Light in the Ocean:
Light from sun (Electromagnetic radiation)
Light quickly scattered or absorbed by gases, particles, organisms
Ocean is divided into 2 zones based on the amount of light received:
1. Photic Zone (sunlit): Nearest surface
 Enough light penetrates water to support photosynthesis (100 meters)
>90% of marine life lives here
2. Aphotic Zone: 90% percent of ocean
 No light
 Cold, high pressure
 No photosynthesis
 Animals eat detritus from above
OR
 Chemosynthesis (Hydrothermal vent bacteria)
 Bioluminescent organisms make their own light
Why is the Ocean Blue?
Light (EMR) is scattered & absorbed (converted into heat) as it passes through water
Blue light travels far enough that some is scattered (reflected) back to the surface
Blue- absorbed last (travels to 294 m)
Infrared & Red absorbed 1st (99% in 1st 4m)
Many marine organisms use sound to “see” in the ocean
Sound waves travel much father through water than air (5X)
Echolocation (sonar): locate objects (size, shape, inorganic or living) by echoes received
back from their own emitted sounds