1. VARIATIONS IN SALINITY OF SEAWATER
GEOL 1033
(Lessons 22-23, 25, and parts of Lesson 24)
(ppt file b)

2. Salinity Variations with Latitude
Low at “meteorological equator” at about 5 º N lat. (=rainforests on continents)
Highs at about 25 deg. N and 15 deg. S
(= desert climatic belts on continents)

3. Salinity Variations with Latitude & Depth
Latitudinal variations with depth
Depth profiles show variations
Subtropics high at surface
Arctic varies seasonally
Lower during melting sea ice
Higher during ice formation (dashes)
34 ppt
37 ppt
Arctic
Subtropics 1 2 3 4 km

4. Major Gases in the Atmosphere and Seawater
Atmospheric gases (more soluble in colder, deeper water) are saturated at all depths except oxygen & carbon dioxide
Oxygen & carbon dioxide are involved in biological processes:
Photosynthesis
Respiration
Decay of organic matter
Argon % %
(as HCO3-)

5. Oxygen & Carbon Dioxide in Seawater
Photic zone consumption of CO2 & production of O2
Photosynthesis: CO2 + H2O  organic matter + O2
Aphotic zone respiration & decay
Produces CO2 & consumes O2
High latitude density circulation “sinks” O2 to deep water

6. Many Factors of Carbon Dioxide Cycle in Seawater
Photosynthesis
Respiration
Decay of organic matter
Atmospheric gas
Carbonic acid
Bicarbonate ion
Carbonate ion
Mg and Ca carbonates - inorganic precipitation
Calcium carbonate skeletons (forams, clams, corals, etc.)
Loss of carbon in organic matter buried in sediments
C in OM in sediments often generates oil & gas deposits
CCD

7. The pH Scale Average pH of seawater is about 7.8 Buffered by CO2
Prevents sudden and wide changes in pH
With a pH decrease, CaCO3 in skeletons & sediments dissolves
With a pH increase, CaCO3 precipitates

8. Carbon Dioxide in Seawater

9. Surface Seawater Calcium Carbonate Saturation
CO2 is more soluble in colder water
It forms carbonic acid (H2CO3) which dissociates to H+ ion & a bicarbonate ion (HCO3-)
H2CO3 dissolves CaCO3
One H+ ion links to the CO32- carbonate to form another bicarbonate (HCO3-) ion
This binding of the H+ stops seawater from becoming more acidic
Removal of CO2 gives up the H+ in HCO3- & reprecipitates CaCO3.
The freed H+ left behind lowers the pH back to normal.

10. Chlorinity “Law of constant proportions” Determine Cl- content in g/kg
Major and many minor constituents have a constant ratio between each other = “conservative” substances
Why?
Possibly due to the oceans being fairly well-mixed
Because of long residence times, especially sodium & chloride
Determine Cl- content in g/kg
The units g/kg are equivalent to ppt (o/oo)
Easier than determining all the salts
Cl- Related to the electrical conductivity & temperature
Multiply this value by the constant to get salinity
Example: g/kg x = o/oo total salinity
Accurate to + or – 0.005
Determine on shipboard or onshore

11. Residence Time
Residence times help to explain why some ions are more abundant than others

12. Greatest Salinity Variations
Air-sea interface
Boundaries between different ocean currents
Coastal areas
Evaporative salt concentration or freshwater dilution
May 29, 1985:
Blomidon = o/00
Kingsport = 16.3 o/00
Latitude
Depth

13. Stopped here

14. Nutrients Less abundant than the dissolved atmospheric gases
Measure in ppm
Many are in limited supply, for example:
Nitrite
Nitrate, sometimes the “limiting factor”
Ammonium
Phosphate, can be the limiting factor
Silica, SiO2, can be the limiting factor
CaCO3, can be the limiting factor
Divergences recycle nutrients back to the photic zone:
Equatorial
Polar
Upwellings also return them to the photic zone

15. Biological Production of Organic Matter in Present-Day World Oceans
Coastal & continental shelves = highest biological productivity
Upwelling
Areas = high
lowest
Divergences

16. END OF FILE

17. 50 60 70 80 F D C B A 6 15 28 27 22
Average = 70%

18. Unit = mL/L
At 1 atm at sea level
STP = standard temperature & pressure

19. ELEMENT ABUNDANCE IN THE CRUST and WHOLE EARTH
Abundance of elements in the crust by percentage weight:
Oxygen O 47
Silicon Si 28
Aluminum Al 8
Iron Fe 5
Calcium Ca 3.6
Sodium Na 3
Potassium K 2.6
Magnesium Mg 2
all others
Whole Earth order of abundance:
Iron Fe 35
Oxygen O 30
Silicon Si 15
Magnesium Mg 13
Nickel Ni 2.4
Sulfur S 2
Calcium Ca 1
Aluminum Al 1
all others <1

20. CHARACTERISTICS OF THE WORLD OCEAN
Oceans cover 71% of Earth's surface (This is equal to about km2 or x 108 km2)
Oceans represent about 98% of Earth's surface and near-surface water (1.37 x 109 km3)
Average depth of the oceans is about 3.8 km (~12,450').
Average temperature of the oceans is about 4 deg. C.
Average salinity is about o/oo (= g/kg)

21. HEAT CAPACITY OF COMMON MATERIALS

25. CROSS SECTIONS OF EARTH
Core (2 layers)
Mantle (3 layers)
Crust (2 types)
Outer core is liquid

26. CROSS SECTIONS OF EARTH
Upper mantle/crustal layers:
lithosphere
asthenosphere
upper mesosphere

27. OVERVIEW OF PLATE TECTONIC PROCESSES
Thermal Convection

29. GL1033x1 Test 2 Results – 9 Nov., 2004 (n=100)F D C B A 4 15 33 31 16
Average = 68%