Daniel H. Rothman
MIT

Topic: Slow Closure of Earth's Carbon Cycle

Abstract:
The carbon cycle's production and consumption of organic carbon must ultimately balance.  Microbes close the loop, but the longer organic matter survives, the slower microbial degradation becomes.  This aging effect leaves observable quantitative signatures: organic matter decays at rates that are inversely proportional to its age, while microbial populations and concentrations of organic carbon in ocean sediments decrease at distinct yet characteristic powers of sediment age.  Yet mechanisms that predict this collective organization remain unknown.  Here I show that these and other observations follow from the assumption that the decay of organic matter is limited by progressively rare extreme fluctuations in the free energy available to microbes.  Predicted scaling laws agree well with observations. The resulting picture suggests that the carbon cycle's age-dependent dynamics are analogous to the slow approach to equilibrium in disordered systems.  The impact of these slow dynamics is profound: they require the accumulation of unoxidized organic carbon in deep sediments, thereby freeing molecular oxygen to accumulate in the atmosphere.

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Academic host: Boz Wing