Abstract
Abstract. The isotopic composition of carbon (Δ14C and δ13C) in atmospheric CO2 and in oceanic and terrestrial carbon reservoirs is influenced by anthropogenic emissions and by natural carbon exchanges, which can respond to and drive changes in climate. Simulations of 14C and 13C in the ocean and terrestrial components of Earth system models (ESMs) present opportunities for model evaluation and for investigation of carbon cycling, including anthropogenic CO2 emissions and uptake. The use of carbon isotopes in novel evaluation of the ESMs' component ocean and terrestrial biosphere models and in new analyses of historical changes may improve predictions of future changes in the carbon cycle and climate system. We compile existing data to produce records of Δ14C and δ13C in atmospheric CO2 for the historical period 1850–2015. The primary motivation for this compilation is to provide the atmospheric boundary condition for historical simulations in the Coupled Model Intercomparison Project 6 (CMIP6) for models simulating carbon isotopes in the ocean or terrestrial biosphere. The data may also be useful for other carbon cycle modelling activities.
Highlights
The isotopic composition of carbon in atmospheric, ocean and terrestrial reservoirs has been strongly perturbed by human activities since the Industrial Revolution
Simulations of the response of plants and photosynthesis to rising atmospheric CO2 and changing water availability can be evaluated with δ13C observations in atmospheric CO2 or in leaves or tree rings, because a close relationship exists between processes controlling leaf-level isotopic discrimination and water-use efficiency (Randerson et al, 2002; Scholze et al, 2008; Ballantyne et al, 2011; Keller et al, 2017; Keeling et al, 2017)
Average differences between annual mean δ13C observations made at Alert for 2005–2015 by Commonwealth Scientific and Industrial Research Organisation (CSIRO) and by the Max Planck Institute for Biogeochemistry are less than 0.01 ‰ (WMO/IAEA, 2016), so the compiled δ13C record we present here can be regarded to be consistent with the VPDB scale established by the Central Calibration Laboratory (CCL)
Summary
The isotopic composition of carbon in atmospheric, ocean and terrestrial reservoirs has been strongly perturbed by human activities since the Industrial Revolution. Studies using 14C and δ13C observations of carbon in the atmosphere, ocean and terrestrial biosphere together with simulated 14C and 13C dynamics in models can provide insights to key processes in the global carbon cycle including air–sea gas exchange, ocean mixing, water use efficiency in plants, and vegetation and soil carbon turnover rates. Simulations of the response of plants and photosynthesis to rising atmospheric CO2 and changing water availability can be evaluated with δ13C observations in atmospheric CO2 or in leaves or tree rings, because a close relationship exists between processes controlling leaf-level isotopic discrimination and water-use efficiency (Randerson et al, 2002; Scholze et al, 2008; Ballantyne et al, 2011; Keller et al, 2017; Keeling et al, 2017).
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