VARIATIONS IN SALINITYOF

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)

km

4

1

2

3

0 Arctic Subtropics

34 ppt 37 ppt

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”– 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

lowestlowest

low

est lowest

lowest

lowest

Divergences

END OF FILE

0

1

2

3

4

5

6

7

8

9

10

1 2 3 4 5 6 7 8 9 101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100

Bins (percent)

F D C B A

50 60 70 80

Average = 70%

6 15 28 22 27

• 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 EARTHUpper 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 A4 15 33 31 16

Average = 68%