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 earth’s crust by the synthesis, death and decomposition of organisms.” Gorham, 1991. Examples: carbon, nitrogen, sulfur, Fe, Mn, etc.

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 Earth’s atmosphere. At present, many biogeochemical cycles are effectively treated as dynamic equilibria among cycled materials. Anthropogenic effects are measurable.

Orbital Variations Eccentricity 100,000 yr Tilt 41,000 yr Precession 23,000 yr

From Albarede, 2003

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 times: water in atmosphere: 11 days water in ocean: 3550 yr Materials can be imported and exported from ecosystems and long-term storage pools.

Basic Biogeochemical Cycle System boundary Inorganic Storage Pool Uplift, mining, etc. Available Abiotic Pool Decomposition (Mineralization) Living Organic Matter Biosynthesis Dead Organic Matter Death Organic Storage Pool

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

(students run screaming from the room)

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