SULFUR CYCLE powerpoint presentation for UG

Sulfur cycle

1. SULFUR CYCLE
Sulfur reservoirs
Driving forces for sulfur transformation
Sulfur in the atmosphere
Sulfur in rivers
Sulfur in the ocean
Global sulfur cycle
Sulfur budget for the ocean
Pyrite formation in sediments
Diagenetic modelling

2. Global Sulfur Cycle
Valence states: +6 (SO
4
2-
) to -2 (sulfides)
Original pool - pyrite FeS
2
Reservoirs,10
18
g S:
Deep oceanic rocks2375 ±820
Sediments 7800±1700
Freshwater0.003±0.002
Ice 0.006±0.002
Atmosphere3.6
Sea 1280±55
Organic5.62x 10
-3

3. Driving Forces: Microbial Transformation
Anaerobic conditions:
sulfate reduction: 2H
+
+ SO
4
2-
+ 2(CH
2
O)->2CO
2
+H
2
S+2H
2
O (Desulfovibrio sp.
or Desulfotomaculum sp.))
–bacteria produce a variety of gases: hydrogen sulfide (H
2
S), dimethyl-sulfide
(CH
3
)
2
S, carboxyl sulfide COS
–H
2
S reacts with Fe
2+
to precipitate FeS, which can be converted to pyrite FeS
2
:
FeS +H
2S > FeS
2 +2H
+
+ 2e-
–H
2
S diffuses though zone of F
3+
2Fe(OH)
3 +3H
2S +2H
+
> FeS
2 + 6H
2O + Fe
2+
sulfur-based photosynthesis (thought to be one of first forms of
photosynthesis on the Earth)
Plant uptake:
assimilatory SO
4
2-
reduction and incorporation of carbon-bounded sulfur
into the amino acids cysteine and methionine.
Aerobic conditions:
reduced sulfur compounds oxidized by microbes, oxidation usually coupled
to reduction of CO
2
in relations of S-based chemosynthesis.

4. •Gaseous component
•no sulfur gas is a long-lived or major constituent of the
atmosphere, oxidation of SO
4
2-
 short residence time, all
expressions in g S
Sulfur in the Atmosphere
•Aerosols
•particles < 1um are held a loft by Brownian motion
•long transport
•sources: volcanic eruptions, ocean, water evaporates from
bubbles, the salt crystallizes to form sea-salt aerosols

5. •Volcanic eruptions
•average over many years 12-30x10
12
g S
•e.g. Tambora (Indonesia) in 1815, 1816 - year without
summer in England, USA, Canada, 50x10
12
g S
Sources of Sulfurof Sulfur in the
Atmosphere
Eriksson (1960) - SO
4
2-
deposition on land from ocean 4x10
12
g S ,
Jung (1960) - SO
4
2-
in rainfall in land 73x10
12
g S,  other sources as sea.
•Soil dust
•Biogenic gases
•H
2S, dimethyl-sulfide (CH
3)
2S, carbonyl sulfide COS
•Anthropogenic emissions
•without human effects, net transport through the
atmosphere carries S from sea to land

6. Sulfur in Rivers
•Human activities affect the transport of S in rivers
•28% of the current content of S in rivers is derived from air
pollution, mining, erosion, and the other human activities
•the current transport is supposed to be about double that
of pre-industrial conditions
•Natural river load
•from weathering of pyrite
4FeS
2+15O
2+8H2O 2Fe
2O
3+8H
2SO
4
•

and gypsum, rainfall

7. Marine sulfur cycle
•Ocean is large source of aerosols (sea salts) that
contains SO
4
2-
.
•Most of the flux is re-deposited in the ocean in precipitation
and dry-fall
•Dimethyl-sulfid (CH
3
)
2
S or DMS is the major biogenic gases
emitted from sea
• annual flux is about 15
•mean residence time about 1-2 days - most of S from DMS is
also re-deposited in the ocean
•The net transport of S from sea to land is about 20x10
12

g S/yr. Ocean receives a net input of S.

8. 10 20
Dust
93 22
Biogenic
gases
Wet and dry deposition84 Transport to sea81
Transport to land
20
Rivers
213
Natural weathering
and erosion
Human mining
and extraction
149
72
10
Pyrit
39
Hydrothermal
sulfides
96
Depo-
sition
258144
Sea
salt
43
Biogenic
gases
From Schlesinger W.H. 1997
Global Sulfur Cycle
all values in 10
12
g S/yr

9. Sulfur budget for the ocean
Pyrite
39
Hydrothermal
vents
96
Rivers
131
Precipitation
& dry fall
247
SO
2
11
DMS
40
Other reduced
gases
<6
Sea salt
144
12 x 10
20
g
From Schlesinger W.H. 1997
all values in 10
12
g S/yr

10. Marine sulfur
cycle
•Content 12x10Content 12x10
20 20
g S/ yr., residence time > 3 000 000 g S/ yr., residence time > 3 000 000
years.years.
•Major marine sinks: metallic sulfides precipitated at Major marine sinks: metallic sulfides precipitated at
hydro-thermal vents, hydro-thermal vents, biogenic pyrites, biogenic pyrites, the formation
of organic sulfur.

11. Dimethylsulfid (CHDimethylsulfid (CH
33))
22S or S or DMS
DMS is the major one of biogenic gases emitted from seaDMS is the major one of biogenic gases emitted from sea
• is produces during decom-is produces during decom-
position of dimethyl-position of dimethyl-
sulfonpropionate (DMSP) sulfonpropionate (DMSP)
from dying phytoplanktonfrom dying phytoplankton
•mean residence time is about mean residence time is about
1-2 days - most of S from DMS 1-2 days - most of S from DMS
is also re-deposited in the is also re-deposited in the
oceanocean
• only small fraction lost into only small fraction lost into
the atmospherethe atmosphere

12. DMS and climate
• oxidation of DMS to sulfate oxidation of DMS to sulfate
aerosols increases the abundance aerosols increases the abundance
of cloud condensation nuclei of cloud condensation nuclei  to to
greater cloudinessgreater cloudiness
• clouds over sea reflect incoming clouds over sea reflect incoming
sunlight sunlight  global cooling global cooling
• layer of sulfate aerosols (known layer of sulfate aerosols (known
as Junge layer) is about 20-25 km as Junge layer) is about 20-25 km
altitude, source: SOaltitude, source: SO
22 and carbonyl and carbonyl
sulfate COSsulfate COS
• production of DMS - net primary production of DMS - net primary
production. production.
• if higher NPP is associated with if higher NPP is associated with
warmer sea surface, then DMS-flux warmer sea surface, then DMS-flux
would have negative feedback on would have negative feedback on
global warmingglobal warming

13. Pyrite Formation in Sediments
Sulfate reduction : SO
4
2-
+ 2(CH
2
O)->2HCO
3
-

+H
2
S
• Reaction H
2S with Fe
2+
or reactive Fe-mineral
4Fe
2O
3+9H
2S ->8FeS+SO
4
2-
+8H
2O+2H
+
• Reaction of iron sulfide with elemental sulfur
FeS + S
0
-> FeS
2
Two steps reaction
incomplete oxidation of H
2S or FeS by
O
2, NO
3-, MnO
2 or FeOOH
Recently
• In strictly anoxic sediments FeS+H2S ->FeS
2
+H
2
• In salt sediments Fe
2+
+ S
0
->FeS
2
From Schultze/Zabel 2000

14. SO
4
2-
ORGANIC MATTER
H
2S
BACTERIA
Fe MINERALS
FeS
BACTERIA
S
0
BACTERIA
FeS
2
PYRITE
Pyrite Formation in Sediments
(after Berner 1972)

15. SO
4
2-
H
2S
O
2
Plants
Bacteria
Fe
2+
FeS
SULFUR IN LAKES