Download September 2, 2009

Origins of the Elements
From: Jacobson
Production of Heavier Elements
4
2
He  He  Be
8
4
Be  He  C
4
2
4
2
8
4
12
6
12
6
C  He  O
16
8
O O S
4
2
16
8
16
8
32
16
Cosmic Composition of Elements
From: Jacobson
Composition of the Earth
• 93% - iron, oxygen, silicon, and
magnesium
• 6.5% - nickel, sulfur, calcium, and
aluminum
• 0.5% - 84 other elements
Composition of the Earth
•
•
•
•
•
Core – iron and nickel
Mantle – iron, magnesium, silicon
Crust – oxygen, silicon
Atmosphere – nitrogen, oxygen
Elements of life – carbon, hydrogen,
oxygen, nitrogen, phosphorous, sulfur
Elements of Life
•
•
•
•
•
•
•
Carbon – structure, energy storage
Hydrogen – water, electron transport
Oxygen – aerobic respiration, water
Nitrogen – amino acids, nitrogenous bases
Phosphorus – ATP
Sulfur – amino acids
Others (Fe, Mg) – enzyme cofactors
The Water Cycle
From: Schlesinger
Potential Human Influence on the
Water Cycle
•
•
•
•
Restricted run-off
Groundwater depletion
Reduction in ice-pack
Climate (increased evaporation, increased
precipitation, increased run-off, sea level
rise)
Calculating Lifetime
• If we assume that reservoirs are in steady
state, the lifetime, τ, is the quantity in the
reservoir divided by the sum of all sinks.
• The average τ of water in the atmosphere:
3
13000km
365days

x
 9.6days
3
-1
496000km yr
yr
Chemical cycle diagrams are only
for equilibrium conditions
dm
  sources   sinks
dt
dm
  sources   sinks
dt
dm
S
 kt
 kt
 S - km  m(t )  m(0)e  (1  e )
dt
k
From: Jacob
Pre-industrial Carbon Cycle
From: Jacob
The Human Influenced
Carbon Cycle
From: http://dilu.bol.ucla.edu/home.html
Increase of Atmospheric CH4
From: http://www.ipcc.ch/present/graphics.htm
Increase of Atmospheric CO2
created by Robert A. Rohde
from NOAA published data
From: http://www.ipcc.ch/present/graphics.htm
The Missing Carbon Sink
• Not all the ‘extra’ carbon emitted to the
atmosphere remains there:
• Sources: fossil fuel and tropical forest
burning = (6.0 + 1.6) Pg yr-1
• Increase in atmosphere = 4.0 Pg yr-1
• Missing sink = 3.6 Pg yr-1
• Possible sinks: ocean and terrestrial
biosphere.
Atmosphere/Ocean
Carbon Exchange
• CO2 partitions into water according to Henry’s Law:
H = 3x10-2 M/atm
• The ocean’s buffer system:
CO2( g ) 
 CO 2(aq)
CO 2(aq)  H 2 O (l ) 
 HCO 3( aq)  H (aq)
HCO 3( aq) 
 CO33(aq)  H (aq)
pKa1 = 6.1; pKa2 = 9.2
The ocean’s pH is 8.2
Effects of Rising CO2 on
Ocean Storage
• However, complete ocean mixing can take
hundreds of years.
• Is ocean mixing the only way carbon is
mixed into the ocean? – No, it is assisted
by a biological pump.
The Ocean’s Biological Pump
From: http://calspace.ucsd.edu/virtualmuseum/images/OceansBiologicalPump.html
Effects of Rising CO2 on
Ocean Storage
From: Jacob
Biosphere/Atmosphere Exchange
of Carbon
• Source – burning, decay, and respiration
(CH 2O)n  nO 2 
 nCO2  nH 2O
• Sink – photosynthesis, dissolution into
ocean
h
nCO2  nH 2O (CH 2O)n  nO 2
The Nitrogen Cycle
From: Jacob
Lifetime of N2 in the Atmosphere
• Atmospheric reservoir = 3.9 x 109 Tg
• Sinks = (80+160+80+30+20) Tg yr-1
• Lifetime (τ) = 1.0 x 107 yr (10 millions yrs)
• However, the N2 cycle is heavily disturbed by
human activities.
Active Nitrogen
• Nitrogen Fixation:
N2 
 NH3
N2 
 NO
bacteria
lightning, combustion
• Nitrification:

4
NH 
 NH3( g ) , NO , NO
2
3
• Denitrification:

2

3
NO , NO 
 N 2( g ) , N 2O( g )
Increase of Atmospheric N2O
From: http://www.ipcc.ch/present/graphics.htm
Global Phosphorus Cycle
From: Schlesinger
What Controls Atmospheric O2?
• Remember the reactions:
– These control carbon in the atmosphere, but
do they control oxygen?
photosynthesis
h
nCO2  nH 2O (CH 2O)n  nO 2
respiration, decay
(CH 2O)n  nO 2 
 nCO2  nH 2O
The Coupled Carbon/Oxygen Cycle
From: Jacob
What Controls Atmospheric O2?
• What if photosynthesis stopped?
– 0.8% decrease of O2
– 470% increase of CO2
• What if respiration and decay stopped?
– 0.1% increase of O2
– 100% decrease of CO2
What Controls Atmospheric O2?
• Sources (photosynthesis, anaerobic
metabolism)
h
nCO2  nH 2O 
(CH 2O)n  nO 2
2Fe2O3  8H 2SO 4  15CH 2O bacteria
 4FeS2  15CO2  23H 2O
• Sinks (sedimentary rock weathering)
CH 2O  O 2 
 CO2  H 2O
4FeS2  8H 2O  15O 2 
 2Fe2O3  16H   8SO 24-
What Controls Atmospheric O2?
From: Jacob