3. Water molecule
H2O
Two hydrogen, one oxygen
Bonded by sharing electrons
Bend in geometry creates polarity
Dipolar molecule
4.
5. Dipolar molecule
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
7. Two unusual properties
High surface tension
Hydrogen bonding creates “skin”
Important for living organisms
Capillarity
Universal solvent
Electrostatic bond between dipolar water and
ions
Ocean is salty
10. 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
12. Heat capacity
Heat absorbed or released with
changes in state
Latent heats of
Melting; freezing
Vaporization, evaporation
Condensation
13. Global thermostatic effects
Moderate global temperature
Evaporation removes heat from
oceans
Condensation adds heat to
atmosphere
Heat re-distributed globally
15. Water density
Maximum density at 4o
C
Ice less dense than liquid water
Atomic structure of ice
Ice floats
Increased salinity decreases temperature of
maximum density
18. Seawater
Salinity=total amount of solid material
dissolved in water (g/1000g)
Typical salinity is 35 o/oo or ppt
Brackish (hyposaline) < 33 ppt
Hypersaline > 38 ppt
19.
20. Measuring salinity
Evaporation
Chemical analysis
Principle of Constant Proportions
Chlorinity
Electrical conductivity (salinometer)
21. 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
22. 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
23. 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
24. 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
25. 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
26. 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
27. Acidity and alkalinity
Acid releases H+ when dissolved in water
Alkaline (or base) releases OH-
pH scale measures acidity/alkalinity
Low pH value, acid
High pH value, alkaline (basic)
pH 7 = neutral
28. 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
30. How salinity changes
Salinity changes by adding or removing
water
Salinity decreases by
Precipitation (rain/snow)
River runoff
Melting snow
31. Salinity increases by
Evaporation
Formation of sea ice
Hydrologic cycle describes
recycling of water
33. 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
35. 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
36.
37. 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
38. 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