Exchange rates within the Global Carbon Cycle,
between oceans, atmosphere and terrestrial biosphere – including the anthropogenic
CO2 production – are being traced by concentration and isotope ratio
measurements of atmospheric CO2. The background value of the stable
isotope ratio of oxygen in atmospheric CO2 is determined by oxygen
exchange with the ocean surface waters. During contact with leaf water, the
signature of this then evaporation-enriched groundwater (the extent still being
dependent on plant physiological and environmental parameters), will be
imprinted on CO2 diffusing back out of the leaf stomata. From water
cycle studies the continental effect (Rayleigh-distillation) is known, leading
to precipitation strongly depleted in d18O over e.g. Siberia.
This signal is also transferred into plant material. These main mechanisms
within the 18O-cycle are known or under investigation. The d18O
source
term for atmospheric CO2 derived from biomass burning and
anthropogenic fossil fuel combustion, however, is less well-known.
Author: R.E.M. Neubert, M. Schumacher, H.A.J. Meijer (R dot E dot M dot Neubert at rug dot nl)
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