Transcript AIM: Introduce you to scientific study of the world's

Move Discussion from Wednesday to
Friday
Read for the discussion: ’Climate
Change 2001: The Scientific Basis Summary for Policy Makers’
You can download a pdf from
http://www.ipcc.ch/pub/spm22-01.pdf
Crystal
structure of ice
looking down its
‘c-axis’ (axis of
hexagonal
symmetry)
Ice structure looking oblique to c-axis
Sea water
•Sea water is an aqueous solution; must add or
subtract dissolved constituents by chemical
means
•Cannot filter out dissolved constituents
•Dissolved constituents will not settle out
•Of 92 stable elements, 72 occur in sea water
in measurable amounts
•Most abundant elements dissolved in sea water
are the abundant in the earth’s crust, with two
important exceptions
–Si is abundant in crust but not in sea water
–Cl is abundant in sea water but not in crust
Primary constituent ions in sea water
total salinity = 34.342 parts per thousand = 34.482 PPT = 34.482
per mil = 34.482‰
Negative ions
(in g per kg of sea water)
Cl-1 - 18.98
SO4-2 2.649
HCO3-1 0.14
H2BO3-1 0.026
Br-1 - 0.065 F-1 - 0.001
Primary constituent ions in sea water
total salinity = 34.342 parts per thousand = 34.482 PPT = 34.482
per mil = 34.482‰
Negative ions
(in g per kg of sea water)
Positive ions
(in g per kg of sea water)
Cl-1 - 18.98
SO4-2 2.649
Na +1 10.556
Mg+2 - 1.29
HCO3-1 0.14
H2BO3-1 0.026
Ca+2 - 0.40
K+1 - 0.38
Br-1 - 0.065 F-1 - 0.001 Sr+2 - 0.013 Rest <<<1%
Solute concentrations in sea water
• Composition of sea water is virtually constant worldwide
– ~35‰ salinity measured in all major oceans
– The relative proportions of major solutes nearly constant, even
where salinity is not 35‰
– Can use chloride concentration, e.g., to determine total salinity;
salinity = 1.80665 x chlorinity
• Distinguish between
– Conservative constituents, i.e. the major components of the
dissolved solids, whose relative concentrations are effectively
fixed (i.e. Na+1, Cl-1, or SO4-2)
– Non-conservative constituents, i.e. minor elements whose
concentrations are locally altered by biological activity, physical
processes, etc. (i.e. NO3-1 or PO4-3)
Changes in sea water salinity
• Salinity changes occur near edges of oceans
–Where Amazon River flows into sea, find
nearly fresh water 100 km off shore
–In Persian Gulf, where shallow sea water
evaporates & there is little precipitation or
river recharge, salinity approaches 40‰
–Freezing sea water at high latitudes causes
salinity to approach 38‰
• Generally, however, sea water salinity is
roughly constant, & it appears to have had
this value for a long time
If sea water salinity has
remained constant (oceans
maintained a steady state), how
is that accomplished?
What are the sources of the
dissolved solids we see in the
oceans?
Can river water be the source of the
dissolved constituents in sea water?
• Hydrologic cycle - water evaporates from
ocean, transported over land, falls as rain
water, dissolves rock constituents, & carries
them into ocean basins
–When sea water evaporates, it takes some salts,
but water vapor is effectively fresh water
–When water condenses to form precipitation, it
usually ends up with significant dissolved CO2 & SO2
–Rain water falling on continents is acidic
–Acidic water dissolves the continents
Chemical constituents in river water
Average river water salinity = 0.12‰
actual vs. (estimate of unpolluted value)
Negative ions
(in g per kg of water)
Positive ions
(in g per kg of water)
HCO3-1 0.053
(0.052)
SO4-2 0.0115
(0.0083)
Ca+2 0.0147
(0.0134)
Na+1 0.0072
(0.0052)
SiO40.0104
(0.0104)
Cl-1 0.0083
(0.0058)
Mg+2 0.0037
(0.0034)
K+1 - 0.0014
(0.0013)
Most important dissolved constituents in
sea water and river water
Sea water
River water
• 99% of dissolved components
are
– Cl -1 = ~ 55.1%
– Na+1 = ~ 30.6%
– SO4-2 = ~ 7.7%
– Mg+2 = ~ 3.7%
– Ca+2 = ~ 1.2%
– K+1 = ~ 1.1%
• Salinity = ~35‰
• 99% of dissolved components
are
– HCO3-1 = ~ 48.7%
– Ca+2 = ~ 12.5%
– SiO2 = ~ 10.9%
– SO4-2 = ~ 9.3%
– Cl -1 = ~ 6.5%
– Na+1 = ~ 5.2%
– Mg+2 = ~ 3.4%
– K+1 = ~ 1.1%
• Salinity = ~ 0.12‰
The total mass of dissolved solids
added by rivers is great = ~4 x 109
tons, but cannot simply concentrate
river water (by evaporation) & get
sea water
Some other chemical processes
must occur to change
concentrations of dissolved
constituents
What other processes add or
subtract dissolved constituents to
sea water?
What are the sources of &
sinks for dissolved solids?
Biological activity
• Organisms are ubiquitous in surface waters; many have
tests (shells or hard parts)
• Organisms consume chemical constituents to make tests
• After organisms die, their tests sink
– Some sinking tests dissolve (remember CCD)
– Others accumulate as oozes at the bottom of the
ocean
– Have calcareous & siliceous oozes
– Remove 1-2 x 109 tons of Si+4, Ca +2, & CO3-2 as
CaCO3 & SiO2
Degassing of ocean
• Dissolved gasses escape when bubbles move to
the surface
• Bursting bubbles send small droplets of water
into air
• Largest fall back to sea, but smallest remain
in the air, carrying dissolved constituents
• Degassing may remove as much as 1-2 x 109
tons of all of the primary dissolved
constituents, Na+1, Cl-1, Mg+2, SO4-2, HCO3-1,
etc.
Formation of evaporites
• Move sea water to restricted basin, where there is
little recharge
• Evaporate & concentrate dissolved solids to their
solubility limits
• Form salt crystals, which collect in layers of minerals
(called evaporites)
• Not important now, but was important in geologic past
– Silurian Salina Group in Appalachians & Michigan
Basin, Triassic Muschelcalk in Alps, Jurassic in the
Gulf coast
• Evaporites remove masses of Na+1, Cl-1, Mg+2, SO4-2,
HCO3-1 as halite (rock salt) & gypsum
Silicate clay flocculation
• Silicate clays are common weathering product, & are
often carried into oceans by rivers
• Often clay minerals are missing cations in their
structure
• Clays react chemically on encountering sea water,
taking up Na+1 & K+1
• Clay particles coagulate as a result of their sorption
of Na+1 & K+1 & sink to the bottom
• Entire process = chemical reaction + coagulation +
sinking = flocculation
• Flocculation removes masses of Na+1 & K+1
Hydrothermal vents at MOR (smokers), I
• At MOR, formation of new lithosphere
fractures rock & brings magma to shallow
depths
• Sea water percolates into rock along
fractures, heats up, & rises through the
oceanic crust to escape into sea water at
hydrothermal vents
• Hot water is chemically active &
metamorphoses basalt as it travels through
crust
• Process also alters the types & concentrations
of dissolved solids
Hydrothermal vents at MOR (smokers), II
• Circulation rates are high; one estimate has a
volume equal to all the water in oceans moving
through vent systems in 5-10 Ma
• Vent circulation probably removes masses of
Na+1, Mg+2, SO4-2 from sea water & adds
Ca+2, Si+4, and K+1 to it
• When hot water with high concentrations of
dissolved solids enters the cold sea, minerals
precipitate, causing water to look cloudy or
smoky
• Leads to white & black smokers
River inflow
+1
Degassin g of sea water
Lose Ca+2 , N a +1, Mg+2, HCO3-1 , SO4-2, & Cl-1
Flocculation of
si licate clays
Biogenic oozes
Lose Ca+2 , HCO3-1, & Si+4
Lose Na +1 & K+1
Evaporite
formation
(in s hallows eas n
i arid
climates)
Lose Ca+2 , N a +1, Mg+2,
HCO3-1, SO4-2 , & Cl-1
Meta morphism of oc eanic c rust
+2
+4
Add Ca & Si
Probably add K+1
+1
-2
Lose Na & SO 4
+2
-1
Probablyl ose Mg & Cl
+1
+2
+2
Add K , Na , Ca , Mg ,
HCO 3-1, SO4-2, & SiO2