Reproducibility of Holocene atmospheric CO2 records based on stomatal frequency analysis

Abstract

The majority of the stomatal frequency-based estimates of CO₂ for the Holocene do not support the widely accepted concept of comparably stable CO₂ concentrations throughout the past 11,500 years. To address the critique that these stomatal frequency variations result from local environmental change or methodological insufficiencies, multiple stomatal frequency records were compared for three climatic key periods during the Holocene, namely the Preboreal oscillation, the 8.2 kyr cooling event and the Little Ice Age. The highly comparable fluctuations in the palaeo-atmospheric CO₂ records, which were obtained from different continents and plant species (deciduous angiosperms as well as conifers) using varying calibration approaches, provide strong evidence for the integrity of leaf-based CO₂ quantification.