VARIATIONS IN SALINITY OF SEAWATER

1. VARIATIONS IN SALINITYOFSEAWATER GEOL 1033 (Lessons 22-23, 25, and parts of Lesson 24) (ppt file 103-20b)

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 0 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 0.94% 1.4% (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” • 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 1.80655 to get salinity • Example: 20.00 g/kg x 1.80655 = 36.13 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 = 24.5 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 lowest lowest lowest lowest lowest lowest lowest Upwelling Areas = high Coastal & continental shelves = highest biological productivity Divergences

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17. 50 60 70 80 C B A F D 15 27 6 28 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 1.5 • 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 361 100 000 km2 or 3.611 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 34.482 o/oo (=34.482 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%