BIOGEOCHEMICAL CYCLING: OXYGEN, NITROGEN, SULFUR, MERCURY

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BIOGEOCHEMICAL CYCLINGOXYGEN, NITROGEN, SULFUR,
MERCURY
EPS 200 - Nov 8. 2007
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FAST OXYGEN CYCLE ATMOSPHERE-BIOSPHERE

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

CO2
O2 lifetime 5000 years
Photosynthesis less respiration
O2
orgC
orgC
decay
litter
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however, abundance of organic carbon in
biosphere/soil/ocean reservoirs is too small to
control atmospheric O2 levels
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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
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OXIDATION STATES OF NITROGENN has 5 electrons
in valence shell a9 oxidation states from 3 to
5(nitrate radical in oxidation state 6)
Increasing oxidation number (oxidation reactions)
Decreasing oxidation number (reduction reactions)
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THE NITROGEN CYCLE MAJOR PROCESSES
combustion lightning
fixation
ATMOSPHERE
N2
NO
oxidation
HNO3
denitri- fication
biofixation
deposition
orgN
BIOSPHERE
decay
NH3/NH4
NO3-
SOIL/OCEAN
assimilation
nitrification
weathering
burial
LITHOSPHERE
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BOX MODEL OF THE NITROGEN CYCLE
Inventories in Tg N Flows in Tg N yr-1
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N2O LOW-YIELD PRODUCT OF BACTERIAL NITRIFICATION
AND DENITRIFICATION

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

IPCC 2001
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N2O versus depth in the Greenland Ice sheet.
Constraints on N2O budget changes since
pre-industrial time from new firn air and ice
core isotope measurements S. Bernard, T.
Rockmann, J. Kaiser, J.-M. Barnola, H. Fischer,
T. Blunier, and J. Chappellaz, Atmos. Chem.
Phys., 6, 493503, 2006
N2O in the atmosphere
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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 )
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OXIDATION STATES OF SULFURS has 6 electrons in
valence shell a oxidation states from 2 to 6
Increasing oxidation number (oxidation reactions)
Decreasing oxidation number (reduction reactions)
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THE GLOBAL SULFUR CYCLE
(sources in Tg S y-1)
SO42-
SO2 H2S
ATMOSPHERE 2.8x1012 g S t 1 week
SO2 CS2
COS (CH3)2S
10
deposition
60
runoff
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plankton
OCEAN 1.3x1021 g S t 107 years
coal combustion oil refining smelters
volcanoes
SO42-
microbes vents
uplift
SEDIMENTS 7x1021 g S t 108 years
FeS2
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RISING MERCURY IN THE BIOSPHERE
States with fish mercury advisories
3000-yr record in Swiss bog
Mercury in polar bear fur up 5-12X since 1890
Roos-Baraclough and Shotyk, EST 2003
Dietz et al., EST 2006
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THE MERCURY CYCLE MAJOR PROCESSES
ANTHROPOGENIC PERTURBATION fuel
combustion waste incineration mining
Atomic wt. 80 Electronic shell Xe 4f14 5d10
6s2
oxidation
Hg(II)
Hg(0)
reduction
highly water-soluble
volatilization evapo- transpiration
volcanoes erosion
deposition
particulate Hg
oxidation
Hg(II)
Hg(0)
biological uptake
reduction
uplift
burial
SEDIMENTS
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GLOBAL MERCURY CYCLE (NATURAL)
Inventories in Mg Rates in Mg y-1
Selin et al. 2007
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GLOBAL MERCURY CYCLE (PRESENT-DAY)
Inventories in Mg Rates in Mg y-1
Selin et al. 2007
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Tons y-1
Africa
Australia
Europe
N. America
S. America
Asia
Figure 2. Global trend in mercury anthropogenic
emissions by continent, 1990-2000. Data from
Pacyna et al. 2006a.
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PRESENT-DAY vs. PREINDUSTRIAL ENRICHMENT FACTORS
FOR MERCURY DEPOSITION
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CONTRIBUTIONS TO N. AMERICAN MERCURY DEPOSITION
FROM THE GLOBAL vs. REGIONAL POLLUTION POOL
N. America accounts for only 7 of global anthro.
emission (2000)
Global pool (lifetime 1 y)
Hg(0) Hg(II)
Hg(0) emission (53)
N. American boundary layer
External anthropogenic Oceans Land
reduction
Regional pollution pool
Hg(II)
Hg(II) emission (47)
NORTH AMERICA
cycling and re-emission
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SOURCE ATTRIBUTION FOR U.S. MERCURY DEPOSITION
contribution of N. American sources to annual
total mercury deposition
Legacy anthropogenic re-emitted from soil
on centurial time scale (16)
Natural (32)
North American anthropogenic (20)
Rest of world anthropogenic (31) half cycled
through ocean on annual time scale
Selin et al. , 2007