sulphur cycle

Question 1

common minerals

Answer 1

• pyrite - FeS2
• gypsum - CaSO4 2H2O
• anhydrite - CaSO4

Question 2

overview of cycle

Answer 2

• has localised not global effects due to short residence times
• has massive anthropogenic effects as burning of coal and ore melting released SO2
• important for cloud formation - plankton release over 20 million tonnes of sulphur in the air (as DMS) acting of hygroscopic nuclei

Question 3

sulphur reservoirs

Answer 3

1. lithosphere
2. ocean water
3. ocean sediments
4. soil and terrestrial biota
5. lake and river water
6. marine biota

Question 4

fluxes of sulphur

Answer 4

1. natural
   - largest between ocean and atmosphere - sea salt sulphate
2. post industrialisation
   - consumption from lithosphere highest
   - anthropogenic emissions second
   - aeolian emissions have doubled

Question 5

OCS/COS

Answer 5

• carbonyl sulphide (II)
• produced directly by organisms or oxidised from carbon disulphide (CS2)
• stable in the troposphere
• long residence time
• unreactive
• slowly mixes into stratosphere

Question 6

reaction of OCS in the stratosphere

Answer 6

OCS + hv = S + CO
S + O2 = SO + O
SO + O2 = SO2 + O
- forms a layer of aerosol particles that reflects incoming radiation

Question 7

atmospheric sulphur cycle

Answer 7

release into the atmosphere
- volcanic eruptions
- sea spray
- biogenic emissions
- ff combustion
taken out of atmosphere
- precipitation / wet deposition
- dry deposition

Question 8

sulphur emissions into the atmosphere

Answer 8

1. biogenic emissions (reduced oxidation state)
   - DMS dominates oceanic emissions
   - more mixed over land
2. biomass burning, human activities, volcanoes
   - SO2 released
   - this gradually reacts to So42-

Question 9

sulphur deposition from the atmosphere

Answer 9

1. conversion of so2 to so42- is 1%/h
   - therefore cycling takes place over several days
   - is only direct absorption of gas
2. dry deposition
   - dry Brownian flux
   - gravitational setting
3. wet deposition
   - SO42- in rain water

Question 10

remote ocean S cycle

Answer 10

• assumed closed system (as sea salt ignored)
  sea diagram in book
• unknown processes occur as sea water passes over mid ocean ridges - precipitate pyrite and S compounds

Question 11

what happens at mid ocean ridges

Answer 11

1. as the plates move apart the exposed hot magma heats the water above
2. this causes a circulation of water as water from the sides rush to replace it
3. aqueous sulphate is chemically reduced to sulphide in this journey
4. sulphur friendly elements are precipitated as sulphides where the water emerges = chimney effect
5. the emerging water is rich in hydrogen sulphide (H2S) that bacteria use in chemosynthesis
6. this bacteria is then consumed by organisms - small ecosystem forms around the vents

Question 12

biological S

Answer 12

SRP - sulphate reducing prokaryotes
- gain energy from the electron transfer between organic matter/ hydrogen/ carbon monoxide and electron acceptors