CHAPTER 6: GEOCHEMICAL CYCLES

1
CHAPTER 6 GEOCHEMICAL CYCLES
THE EARTH ASSEMBLAGE OF ATOMS OF THE 92 NATURAL
ELEMENTS

• Most abundant elements oxygen (in solid earth!),
  iron (core), silicon (mantle), hydrogen (oceans),
  nitrogen, carbon, sulfur
• The elemental composition of the Earth has
  remained essentially unchanged over its 4.5 Gyr
  history
• Extraterrestrial inputs (e.g., from meteorites,
  cometary material) have been relatively
  unimportant
• Escape to space has been restricted by gravity
• Biogeochemical cycling of these elements between
  the different reservoirs of the Earth system
  determines the composition of the Earths
  atmosphere and oceans, and the evolution of life

2
BIOGEOCHEMICAL CYCLING OF ELEMENTSexamples of
major processes
Physical exchange, redox chemistry, biochemistry
are involved
Surface reservoirs
3
HISTORY OF EARTHS ATMOSPHERE
N2 CO2 H2O
O2
O2 reaches current levels life invades continents
oceans form
CO2 dissolves
Life forms in oceans
Onset of photosynthesis
Outgassing
4.5 Gy B.P
4 Gy B.P.
0.4 Gy B.P.
3.5 Gy B.P.
present
4
COMPARING THE ATMOSPHERES OF EARTH, VENUS, AND
MARS
5
EVOLUTION OF O2 AND O3 IN EARTHS ATMOSPHERE
6
Source EARLY EARTH Oxygen for heavy-metal fans
Lyons TW, Reinhard CT NATURE Volume 461
Issue 7261 Pages 179-181 SEP 10 2009
7
OXIDATION STATES OF NITROGENN has 5 electrons in
valence shell a9 oxidation states from 3 to 5
Increasing oxidation number (oxidation reactions)
radical
radical
Decreasing oxidation number (reduction reactions)
8
THE NITROGEN CYCLE MAJOR PROCESSES
combustion lightning
ATMOSPHERE
N2
NO
oxidation
HNO3
denitri- fication
biofixation
deposition
orgN
decay
NH3/NH4
NO3-
BIOSPHERE
assimilation
nitrification
weathering
burial
LITHOSPHERE
9
Oceanic Nitrogen Processes
10
(No Transcript)
11
(No Transcript)
12
(No Transcript)
13
BOX MODEL OF THE NITROGEN CYCLE
Inventories in Tg N Flows in Tg N yr-1
14
N2O LOW-YIELD PRODUCT OF BACTERIAL NITRIFICATION
AND DENITRIFICATION

• Important as
• source of NOx radicals in stratosphere
• greenhouse gas

IPCC 2007
15
PRESENT-DAY GLOBAL BUDGET OF ATMOSPHERIC N2O
IPCC 2001
Although a closed budget can be constructed,
uncertainties in sources are large! (N2O atm
mass 5.13 1018 kg x 3.1 10-7 x28/29 1535 Tg )
16

• Vertical and Horizontal Distributions of
  nutrients and dissolved oxygen in the sea
• Summary
• Nutrients (N, P Si) and trace elements (Cu, Zn,
  Fe !) used by plants and animals) are stripped
  from surface ocean and carried into the deep
  ocean by sedimentation.
• Re-mineralization creates excess concentrations
  of these elements, and depletion of oxygen, in
  deep water.
• The mean ratios of elements evolved during
  re-mineralization ("Redfield ratios") appear to
  be very uniform over the ocean, and possibly over
  geologic time, even though the ratios are not
  fixed in individual organisms.
• N2O is evolved during re-mineralization with a
  consistent ratio to O2 uptake. (Yield 3
  N2O NO3- )(mole/mole 6 as N)

17
Atlantic Ocean Deep Vertical Profile (Bermuda
time series station)
18
http//www.soest.hawaii.edu/hioos/oceanatlas/verst
ructure.htm
Pacific Average vertical distribution of
temperature, salinity, and nutrients
(nitratenitrite) at Ocean Station Aloha 1988 to
1995. (World Ocean Circulation Experiment, Hawaii
Ocean Time Series Project, University of Hawaii.
Units degrees Celsius, part-per-thousand of
salt, and µmole/kg of nutrients).
19
GEOSECS WOCE
WOCE
Pacific
O2 min
20
Figure 2 Vertical profiles of first-row
transition metal ions and other elements in the
N. Pacific.
A Butler Science 1998281207-209
21
( )
22
3.4e-3 moleN2O/mole O2 0.03N2O / NO3-
23
N2O and nutrients in the sea
24
HIPPO boat NCAR Gulfstream V "HIAPER"
GV launch in the rain, Anchorage, January, 2009
(HIPPO-1)
25
HIPPO itinerary
HIPPO_2 Nov 2009
preHIPPO Apr-Jun 2008
HIPPO_3 Apr 2010
HIPPO_1 Jan 2009
26
HIPPO-1 Atmospheric Structure (Pot'l T K)
January, 2009, Mid-Pacific (Dateline) Cross
section
27
HIPPO sections, January 2009
CO
CO2
CH4
0 5 10 15 km
0 5 10 15 km
0 5 10 15 km
-60 -40 -20 0 20 40 60
80 -60 -40 -20 0 20 40
60 80 -60 -40 -20 0 20
40 60 80


N2O
SF6
O3
0 5 10 15 km
0 5 10 15 km
0 5 10 15 km
-60 -40 -20 0 20 40 60
80 -60 -40 -20 0 20 40
60 80 -60 -40 -20 0 20
40 60 80

LATITUDE
28
CH4
CO
Jan 2009
CO2
0 5 10 15 km
CO
CO2
CH4
Nov 2009
0 5 10 15 km
-60 -40 -20 0 20 40 60 80 -60
-40 -20 0 20 40 60 80 -60 -40
-20 0 20 40 60 80

LATITUDE
29
N2O
O3
January 2009
0 5 10 15 km
-60 -40 -20 0 20 40 60 80
-60 -40 -20 0 20 40 60 80
November 2009
0 5 10 15 km
-60 -40 -20 0 20 40 60 80
-60 -40 -20 0 20 40 60 80
LATITUDE

30
Other tracers confirm N2O variable layers arise
from different air origins CO2 CH4 CO
31
HIPPO Nitrous Oxide (N2O)
Observed vs Model (ACTM)
Prabir Patra, Kentaro Ishijima (JAMSTEC) Eric
Kort (Harvard)
HIPPO_1 Jan 2009
32
ACTM Eric Kort (Harvard) Prabir Patra,
Kentaro Ishijima (JAMSTEC)
33
ACTM model (optimized for ground
stations) Excellent fit to surface observations
64 surface stations, monthly means (courtesy K.
Ishijima)
34
Observed ACTM Prior
Jan., S-bound
Jan., N-bound
Nov., S-bound
Nov., N-bound
35
SF6
CH4
N2O HIPPO-2
N2O
36
Global Distribution of N2O emissions HIPPO
cross sections, ACTM Model
Global Totals (Tg N in N2O, over 63 days)
6.4 Posterior
4.8 3.2
Prior 3.15
Eric Kort (Harvard) Prabir Patra, Kentaro
Ishijima (JAMSTEC)
37
Inversion results by region HIPPO-1
HIPPO_2
38
BOX MODEL OF THE NITROGEN CYCLE
Inventories in Tg N Flows in Tg N yr-1
39
BOX MODEL OF THE N2O CYCLE
40
PRESENT-DAY GLOBAL BUDGET OF ATMOSPHERIC N2O
IPCC 2001
Although a closed budget can be constructed,
uncertainties in sources are large! (N2O atm
mass 5.13 1018 kg x 3.1 10-7 x28/29 1535 Tg )
41
FAST OXYGEN CYCLE ATMOSPHERE-BIOSPHERE

• Source of O2 photosynthesis
• nCO2 nH2O g (CH2O)n nO2
• Sink respiration/decay
• (CH2O)n nO2 g nCO2 nH2O

8x102 Pg
O2 lifetime 6000 years vs Photosynthesis 200
PgO/yr
CO2
1.2x106 Pg
Photosynthesis less respiration
O2
orgC
orgC
decay
litter
4x103 Pg
42
SLOW OXYGEN CYCLE ATMOSPHERE-LITHOSPHERE
O2 lifetime 3 million years
O2 1.2x106 Pg O
CO2
O2
Photosynthesis decay
runoff
Fe2O3 H2SO4
weathering
CO2
O2
orgC
FeS2
OCEAN
CONTINENT
orgC
Uplift
burial
CO2
orgC 1x107 Pg C FeS2 5x106 Pg S
microbes
FeS2
orgC
SEDIMENTS
Compression subduction
43
however, abundance of organic carbon in
biosphere/soil/ocean reservoirs is too small to
control atmospheric O2 levels
44
Antarctic Ice Core Data
CO2 varies over geologic time, within the range
190 280 ppm for the last 420,000 years. The
variations correlate with climate cold ? low
CO2 . Is CO2 driving climate or vice versa?
The heavier temperature lines 160,000 BP to
present reflect more data points, not necessarily
greater variability.
Source Climate and Atmospheric History of the
past 420,000 years from the Vostok Ice Core,
Antarctica, by Petit J.R., Jouzel J., Raynaud D.,
Barkov N.I., Barnola J.M., Basile I., Bender M.,
Chappellaz J., Davis J. Delaygue G., Delmotte M.
Kotlyakov V.M., Legrand M., Lipenkov V.M., Lorius
C., Pépin L., Ritz C., Saltzman E., Stievenard
M., Nature, 3 June 1999.
45
GLOBAL PREINDUSTRIAL CARBON CYCLE
Inventories in Pg C Flows in Pg C a-1
46
7800 in 2005! 8200 in 2007!
6500
1990
Global Fuel Use
1980
1970
3800
History of consumption of fossil fuels. Emissions
have increased by more than 2X since 1970. There
rise in the last 5 years has been really
dramatic. But there has not been a corresponding
rise in the annual increment of CO2. In 1970
75 of the emitted CO2 stayed in the atmosphere,
but only 40 in 2000.
1960
1950
Year
47
Antarctic ice cores compared with modern data for
CO2
48

CO2
Atmospheric increase 57 of fossil fuel
emissions Interannual variability correlated
with El Niño
Arrows indicate El Nino events
49
The rate of CO2 accumulation in the atmosphere
has risen on a decadal time scale, from 0.7
ppm/yr in the 1960's to 1.8 ppm/yr in the
2000's. The 1980's and 1990's were(slightly)
anomalous.
50
0.57
51
Composition of Sea Water
Charge balance in the ocean HCO3- 2CO32-
Na K 2Mg2 2Ca2 - Cl-
2SO42- Br- The alkalinity Alk
HCO3- 2CO32- 2.3x10-3M
"alkalinity" defines S' Zi i response of
H and OH- to addition of CO2
52
UPTAKE OF CO2 BY THE OCEANS
ATMOSPHERE
KH 3x10-2 M atm-1
OCEAN
K1 9x10-7 M
Ocean pH 8.2
pK1
HCO3-
CO32- H
K2 7x10-10 M
pK2

CO2.H2O
HCO3-
CO32-
53
LIMIT ON OCEAN UPTAKE OF CO2CONSERVATION OF
ALKALINITY

• Charge balance in the ocean
• HCO3- 2CO32- Na K 2Mg2
  2Ca2 - Cl- 2SO42- Br-
• The alkalinity Alk HCO3- 2CO32-
  2.3x10-3M is the excess base relative to the
  CO2-H2O system
• It is conserved upon addition of CO2
• uptake of CO2 is limited by the existing supply
  of CO32-
• Increasing Alk requires dissolution of sediments

2.1
2.0
CO2.H2OHCO3- CO32-, 10-3M
1.9
1.8
HCO3-, 10-3M
1.6
1.4
4
CO32-, 10-4 M
3
2
8.6
Ocean pH
8.4
8.2
which takes place over a time scale of thousands
of years
54
NCO2atmPCO2 Natm NCO2aq PCO2KH Voc (1
K1/H K1 K2 / H2 )

CO2 aq HCO3-
CO3 1
140 16 CO2?H2O ? HCO3- H
K1 HCO3- H / CO2?H2O HCO3-
? H CO3 K2 CO3
H / HCO3- HCO3- ( K1 / H )
CO2?H2O CO3 ( K2K1 / H 2 )
CO2?H2O
55
EQUILIBRIUM PARTITIONING OF CO2BETWEEN
ATMOSPHERE AND GLOBAL OCEAN

• Equilibrium for present-day ocean

• only 3 of total inorganic carbon is currently
  in the atmosphere

But CO2(g) k H k F k positive feedback
to increasing CO2
Pose problem differently how does a CO2 addition
dN partition between the atmosphere and ocean at
equilibrium (whole ocean)?
28 of added CO2 remains in atmosphere!
56
b (buffer factor) Sundquist et al. 1979
57
FURTHER LIMITATION OF CO2 UPTAKE SLOW OCEAN
TURNOVER ( 200 years)
Inventories in 1015 m3 water Flows in 1015 m3 yr-1

• Uptake by oceanic mixed layer only (VOC 3.6x1016
  m3)
• would give f 0.94 (94 of added CO2 remains
  in atmosphere)

58
Observed penetration of fossil fuel CO2 into the
oceans
comp to 300 µmoles/kg CO3
59
CYCLING OF CARBON WITH TERRESTRIAL BIOSPHERE
Inventories in PgC Flows in PgC a-1
60
EVIDENCE FOR LAND UPTAKE OF CO2 FROM TRENDS IN
O2,1990-2000
61
NET UPTAKE OF CO2 BY TERRESTRIAL BIOSPHERE(1.4
Pg C yr-1 in the 1990s IPCC 2001)is a small
residual of large atm-bio exchange

• Gross primary production (GPP)
• GPP CO2 uptake by photosynthesis 120 PgC yr-1
• Net primary production (NPP)
• NPP GPP autotrophic respiration by green
  plants 60 PgC yr-1
• Net ecosystem production (NEP)
• NEP NPP heterotrophic respiration by
  decomposers 10 PgC yr-1
• Net biome production (NBP)
• NBP NEP fires/erosion/harvesting 1.4 PgC
  yr-1

62
GLOBAL CO2 BUDGET IN 1980s AND 1990s (Pg C a-1)
IPCC 2001
IPCC 2001
63
HUMAN INFLUENCE ON THE CARBON CYCLE
Natural fluxes in black anthropogenic
contribution (1990s) in red
64
7800 in 2005! 8200 in 2007!
6500
1990
Global Fuel Use
1980
1970
3800
History of consumption of fossil fuels. Emissions
have increased by more than 2X since 1970. There
rise in the last 5 years has been really
dramatic. But there has not been a corresponding
rise in the annual increment of CO2. In 1970
75 of the emitted CO2 stayed in the atmosphere,
but only 40 in 2000.
1960
1950
Year
65
2007
66
(No Transcript)
67
China is projected to have exceed US emissions in
2009. slide from the previous offering of EPS
133.
68
China did exceed US emissions, in 2007...
Emissions (Pg C/yr) 0 .5 1
1.5 2
USA
China
India
69
Per Capita Fossil Fuel Use since 1950, selected
countries
USA
UK
China
India
70
PROJECTIONS OF FUTURE CO2 CONCENTRATIONSIPCC,
2001
71
PROJECTED FUTURE TRENDS IN CO2 UPTAKEBY OCEANS
AND TERRESTRIAL BIOSPHERE
Feedbacks
IPCC 2001
72
(No Transcript)