Compiled records of atmospheric CO2 concentrations and stable carbon isotopes to reconstruct climate and derive plant ecophysiological indices from tree rings

The stable carbon isotopic composition (delta C-13) measured in tree rings is a standard proxy for paleoclimate reconstructions and is increasingly being used as a paleophysiological proxy. To fully exploit the potential of tree ring delta C-13 proxy, atmospheric CO2 concentration and delta C-13 (delta(CO2)-C-13) data are required to correct tree ring delta C-13 from the declining trend of delta(CO2)-C-13 due to fossil fuel burning since 1850 CE, and to derive physiological parameters using biochemical models that link photosynthesis to delta C-13. These atmospheric data are available from direct measurements or can be inferred from indirect proxies such as ice cores covering the Common Era (CE) at variable temporal resolutions. For almost two decades, tree-ring researchers have relied on a dataset derived from fitted linear regressions of ice core measurements available through the seminal McCarroll and Loader (2004) article for the 1850 2003 CE period. However, new calibrations and compilations of ice core data and direct measurements are now available as part of Earth System Modelling efforts which remain overlooked by the tree ring research community. Here, we present an overview of the new and freely available datasets and provide recommendations for their use in ecophysiology and paleoclimate research, that we expect will stimulate cross-disciplinary collaborations.