1. Chapter 6: Water and Seawater
Fig. 6-19

2. Atomic structure
Atoms:
• Building blocks of all
matter
Structure:
• Nucleus (nucleos = little
nut)
Inside of the Nucleus:
• Protons (+ charge) and
neutrons (no charge)
Surrounding Nucleus:
• Electrons (- charge)
• Ions are charged atoms
and can be lost or
gained

3. Protons
• The number of protons is what distinguishes
atoms of the 115 known chemical elements.
Example:
• An atom of Oxygen (O) has 8 protons, no
other element will have 8 protons.
• An atom of Hydrogen (H) has only 1 proton
and an atom of Helium (He) has only two
protons

4. Water molecule
Molecule (molecula = a mass): group of
two or more atoms
Water Molecule (H2O)
• Two hydrogen, one oxygen
• Covalent Bond (bonded by sharing
electrons)
• Bend in geometry creates polarity
• Dipolar molecule

5. Water molecule

6. Covalent Bonding (electron sharing)

7. Polarity
• Water molecule has a bent geometry:
– Causes:
• Overall (-) charge to side of O atom
• Overall (+) charge to side of H atom
• The separation of the charges gives the
molecule an electrical polarity
• Specifically, the water molecule is dipolar
– Other common dipolar objects:
• Flashlight batteries, car batteries, bar magnets

8. Dipolar molecule
di = two, polus = pole
• Water molecules behave like they have a
tiny bar magnet inside
• 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

9. Two unusual properties
1. High surface tension
– Hydrogen bonding creates “skin”
– Important for living organisms
• Capillarity
1. Universal solvent
– Electrostatic bond between dipolar
water and ions
– Ocean is salty

10. Hydrogen Bond

11. Hydrogen Bonds
Hydrogen Bond: between water molecules is
much weaker than the covalent bonds that
hold
individual water molecules together.
• Even though weaker than covalent bond still
strong enough to show cohesion.
– Cohesion causes water to bead up on a waxed
surface
• Cohesion also gives water its surface
tension.

12. Surface Tension
Water Piling Up)
• Results from formation of
hydrogen bonds between
outermost layer of water
molecules and underlying
molecules (allowing water
to “pile up”)
• Capillarity: causes water Capillarity
to climb up the side of a
container due to the
attraction between the (+)
charge of water molecules
and the (– )charge of the
surface of the glass

13. Water: The Universal Solvent
• Water sticks not only to other water
molecules but also to other polar chemical
compounds  this means that water
molecules can reduce the attraction between
ions of opposite charges by as much as 80
times.
• The reduced attraction allows water to
dissolve nearly everything (everything polar
that is).
• Na+Cl- is dissolved very easily so the oceans
are salty.

14. Na+ & Cl- ions Dissolved in Water
Fig. 6-5b

15. 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

16. Thermal Properties
Water’s Thermal Properties:
• Influence world’s heat budget
• Moderate coastal temperatures
• In part responsible for development of
tropical cyclones, worldwide wind belts,
and ocean surface currents

17. Changing States of Matter
• Add or remove Heat
• Heat: is the energy of moving molecules. It is
proportional to the energy level of molecules
and therefore, is the total kinetic energy of a
substance
• Calorie: the amount of heat required to raise
the temperature of 1 gram of water (~10
drops) by 1 degree centigrade.
• Temperature: direct measure of the average
kinetic energy of the molecules that make up
a substance.

19. Heat Capacity
• Amount of heat required to raise the
temperature of 1 gram of any substance by 1
degree centigrade.
• Water has the highest heat capacity and is
exactly 1 calorie per gram (other substances
are lower)
• High Heat Capacity  absorb (or lose) great
amounts of heat with only a small change in
temperature.
• Low Heat Capacity  substances that
change temperature rapidly when heat is
applied or taken away.

20. Water’s Latent Heats
• Water undergoes changes of state.
• During the changes: large amounts of heat is either
absorbed or released because of water’s high latent
(latent = hidden) heats.
• These latent heats are closely related to water’s
unusually high heat capacity.
• Examples:
– as water evaporates from your skin, it cools your body by
absorbing heat (this is why sweating cools your body)
– Opposite extreme: being scalded by water vapor/steam
releases the latent heat onto your skin and gives you a
severe burn when it condenses on your skin.

21. Fig. 6-7

24. Global thermostatic effects
• Moderate global temperature
• Evaporation removes heat from
oceans
• Condensation adds heat to
atmosphere
• Heat re-distributed globally

25. Differences in day and night temperatures

26. Water density
• Maximum density at 4oC
• Ice less dense than liquid water
– Atomic structure of ice
– Ice floats
• Increased salinity decreases
temperature of maximum density

29. Why Does Ice Float?
• Density of most substances increases as it
temperature decreases (ex: cold air sinks, warm air
rises).
• Density increases as temperature decreases
because the molecules lose energy and slow down
(so, same number of molecules occupy less space)
 thermal contraction
• This also occurs in water but only to a certain point
(to ~ 4oC (39oF).
• From 4oC down to 0oC, its density decreases 
water stops contracting and actually expands
causing it to be less dense than liquid water.

30. Seawater
• Contains dissolved substances that give it a
salty taste.
• Dissolved substances are not strictly sodium
and chloride but various salts, metals, and
dissolved gases.
Salinity:
• The total amount of solid material dissolved
in water (including gases  some become
solids at low enough temperatures)

31. Salinity of Seawater
• 3.5% (35 0/00 ppt (parts per thousand))
• ~220 times saltier than fresh water.
• Seawater with a salinity of 3.5% indicates
that it also contains 96.5% pure water.
• Physical properties are similar to those of
pure water.

32. Parts Per Thousand (ppt)
• A unit of measurement used in reporting
salinity of water equal to the grams of
dissolved substances in 1000 grams of
seawater.
• 10/00 is one part in 1000.
• When converting from percent to ppt, the
decimal is moved over one place to the right
(ex: 3.5% = 350/00)
• Advantages of Expressing Salinity in ppt:
– Decimals are avoided and values convert to
grams of salt per kilogram of seawater (ex: 35 0/00
seawater has 35 g of salt in 1000 g of seawater.

35. Salinity Variations
• Open Ocean: varies between 33 and 38 o/oo
• Brackish: (brak = salt, ish = somewhat)
– Produced in areas where fresh water and seawater mix
– Average salinity is ~ 10 o/oo (ex: Baltic Sea)
• Hypersaline: (hyper = excessive, salinus = salt)
– Typical of seas and inland bodies of water that experience
high evaporation rates and limited open-ocean circulation
– Salinities are well above 35 o/oo
– Examples: Red Sea 42 o/oo, Great Salt Lake in Utah 280
o/oo, The Dead Sea 330 o/oo (10 times saltier than
seawater)
• Salinity of seawater also varies seasonally on
coastal areas. Evaporation rates change throughout
the year affecting salinity values.

36. Measuring Salinity
• Evaporation
– Evaporate a weighed amount then weighed salts that
precipitated from it.
• Chemical analysis
– Principle of Constant Proportions
• Major constituents of ocean-water salinity found in
same relative proportions throughout the ocean-water
volume, independent of salinity
– Chlorinity
• Amount of chloride ion(s) of other halogens in ocean
water expressed in ppt(0/00) by weight.
• Salinometer
– Instrument that uses electrical conductivity to determine
salinity of ocean water

37. Electrical Conductivity

38. Why Salinity Varies: 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

40. 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

42. 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

43. 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

44. 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

45. • 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

46. Acidity and alkalinity
• Acid releases H+ (hydrogen ion) when
dissolved in water
• Alkaline (or base) releases OH-
(hydroxide ion)
• pH scale measures acidity/alkalinity
– Low pH value, acid
– High pH value, alkaline (basic)
– pH 7 = neutral

48. 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

49. Fig. 6-17

50. How salinity changes
• Salinity changes by adding or
removing water
• Salinity decreases by
– Precipitation (rain/snow)
– River runoff
– Melting snow

51. • Salinity increases by
– Evaporation
– Formation of sea ice
• Hydrologic cycle describes recycling
of water

53. Hydrologic cycle
Fig. 6-19

54. 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

55. Fig. 6-20

56. 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

59. 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

60. • 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
• Plimsoll Line, loading mark painted on the hull of
merchant ships, it shows the depth to which a
vessel may be safely (and legally) loaded.

61. Pycnocline and Thermocline

64. Layers of ocean
• Mixed surface
layer
• Pycnocline
• Deep ocean

65. Major Gases in Atmosphere & Ocean