Transcript 103-20b-VariationSalinitySeawater

VARIATIONS IN SALINITY
OF
SEAWATER
GEOL 1033
(Lessons 22-23, 25, and parts of Lesson 24)
(ppt file 103-20b)
Salinity
Variations
Latitude
Salinity
Variationswith
with Latitude
Salinity (ppt)
Low
at “meteorological equator”
at about
5 º N lat.
• Low• at
“meteorological
equator”
at about
5 (=rainforests
º N lat.
on continents)
(=rainforests
on continents)
• Highs at about 25 deg. N and 15 deg. S
• Highs at (=
about
deg.belts
N and
15 deg. S
desert25
climatic
on continents)
(= desert climatic belts on continents)
North-South Salinity Variations
37
35
33
60 N
40
20
0
Latitude
20
40
60 S
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
0
1
2
3
4
km
Arctic
37 ppt
Subtropics
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
(as HCO3-)
Argon
0.94%
1.4%
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 CO32carbonate 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.
Earth's Ocean Surfaces
north
unsaturated
-------------------- 30
-------equator--------------------------- 30
Saturated
with
CaCO3
unsaturated
south
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
lowest
lowest
lowest
lowest
lowest
Upwelling
Areas = high
Coastal & continental shelves = highest biological productivity
Divergences
END OF FILE
50
60
F
D
6
15
70
80
C
28
B
22
A
27
38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94
Bins (percent)
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
Silicon
Aluminum
Iron
Calcium
Sodium
Potassium
Magnesium
all others
O
Si
Al
Fe
Ca
Na
K
Mg
47
28
8
5
3.6
3
2.6
2
1.5
• Whole Earth order of abundance:
–
–
–
–
–
–
–
–
–
Iron
Oxygen
Silicon
Magnesium
Nickel
Sulfur
Calcium
Aluminum
all others
Fe
O
Si
Mg
Ni
S
Ca
Al
35
30
15
13
2.4
2
1
1
<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
4
15
C
33
B
A
31
16
Average = 68%