Biogeochemistry and Biogeochemical Cycles

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Biogeochemistry and Biogeochemical Cycles

• Definitions
• the more or less circular transfer of chemical
  elements from the (abiotic) environment to the
  organisms and from organisms back to the
  (abiotic) environment. Odum, 1971.
• the study of the controls on the concentrations
  and cycling of elements in and above the earths
  crust by the synthesis, death and decomposition
  of organisms. Gorham, 1991.
• Examples
• carbon, nitrogen, sulfur, Fe, Mn, etc.

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Big Picture

• Over the long term, biogeochemical cycling has
  played a fundamental role in planetary evolution
  on Earth (especially the atmosphere and
  hydrosphere).Example rise of O2 in Earths
  atmosphere.
• At present, many biogeochemical cycles are
  effectively treated as dynamic equilibria among
  cycled materials.
• Anthropogenic effects are measurable.

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Orbital Variations
Eccentricity100,000 yr
Tilt 41,000 yr
Precession23,000 yr
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From Albarede, 2003
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Residence Time (steady state)Response Time (non
steady-state)

• Definition Average time the substance spends in
  the reservoir. It is the time required to double
  the concentration in a reservoir (if output
  ceased).
• Ri amti in reservoir/fluxi Example residence
  timeswater in atmosphere 11 days water in
  ocean 3550 yr
• Materials can be imported and exported from
  ecosystems and long-term storage pools.

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Basic Biogeochemical Cycle
System boundary
Available Abiotic Pool
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Major, Minor, and Trace Elements in
Biogeochemical Cycles

• Major elemental components of living organisms
  (C, H, O, N, P, S)
• Carbohydrates, proteins, lipids, nucleic acids
• Minor elements Ca, K, Mg, Na, Si
• Trace elements B, Co, Cr, Cu, Fe, Mn, Mo, Ni,
  Se, Sn, V, Zn, REEs
• Ca and Si are only minor components of
  protoplasm, but are major components of exo and
  endoskeletons of microorgs and macroorgs
• Fe, Mn, N, S are also cycled rapidly via redox
  processes which may not be directly coupled to
  the production and decay of organic matter

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A Partially Open Biogeochemical Cycle The
Oceanic Carbon System
Atmosphere
CO2
Shallow Sea
Dissolved Inorganic Carbon
EXCHANGE OF WATER
EXCHANGE OF WATER
Organically-Bound Carbon
Organic carbon
Carbonate particles
Long-term removal
Deep Sea
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