Carbon Oxidation State

Every organic carbon pool has an associated oxidative ratio (OR) value, where OR is defined as the moles of O2 emitted during photosynthesis per moles of CO2 fixed (O2/CO2), or the moles of O2 consumed per mole of CO2 emitted for reverse processes (e.g. respiration, fire, etc.). This exchange ratio between O2 and CO2 in the biosphere is an Earth system tracer, with a natural span of values ranging from 0 (CO2) to 2.0 (CH4). OR values for the atmosphere, terrestrial biomass, and soil samples typically fall in the range of 0.8 – 1.2 [Severinghaus, 1995; Masiello et al., 2008; Hockaday et al., 2009; Worrall et al., 2013; Clay and Worrall, 2015a; Gallagher et al., 2014; van der Laan et al., 2014].

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Like many other organic matter tracers, OR can be both a property of a pool or a flux. This is analogous to δ 13 C, which can be measured in biomass, litter, soils, sediments, or atmospheric samples. Like the δ 13 C signature of the photosynthetic flux, the OR associated with photosynthesis can be constrained through gas measurements, or it can be estimated after CO 2 has been fixed by measuring the signature retained in biomass, soils, or sediments.

We are building out the use of this tracer in the Earth system. Want to join us? Ideas for collaboration? Contact us!

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