VARIATIONS IN SALINITY OF SEAWATER GEOL 1033 (Lessons 22-23, 25, and parts of Lesson 24) (ppt file 103-20b)

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)

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

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-)

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

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

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

Carbon Dioxide in Seawater

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.

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 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

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

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

Stopped here

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

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

END OF FILE

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

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

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

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)

HEAT CAPACITY OF COMMON MATERIALS

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

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

OVERVIEW OF PLATE TECTONIC PROCESSES Thermal Convection

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