Thirty-two years of high precision data on the stable isotopes of carbon dioxide from a successful collaboration between NOAA and INSTAAR

Monitoring the long-term changes in the stable carbon isotope ratio of carbon dioxide (expressed as δ¹³C-CO₂) is a useful tool to track the fate of atmospheric CO₂ and variations in the global carbon cycle. Due to the small but significant change in global mean atmospheric δ¹³C-CO₂ of approximately -0.75‰ over the last three decades, a robust and traceable method is required to track the long-term change in δ¹³C-CO₂ globally. The Stable Isotope Lab at the INSTAAR of the University of Colorado Boulder has been partnering with NOAA’s Global Monitoring Laboratory since 1990 to measure CO₂ stable isotopes within the Global Greenhouse Gas Reference Network. Here, we present our latest data product, globally distributed observations of δ¹³C-CO₂ in the past 32 years. We have improved our traceability by moving our data onto the CO₂ -in-air JRAS-06 isotopic scale (a representation of V-PDB). We also have established robust quality management systems and have improved our methods of quantifying uncertainty.  Our data demonstrate how the interactions among the atmosphere, the biosphere and anthropogenic activities had been recorded in δ¹³C-CO₂ from more than 70 sites worldwide. The data reveal distinct seasonal variations of δ¹³C-CO₂ that change with latitude, highlighting spatial differences in the influence of anthropogenic activities, net photosynthesis, and ocean-atmosphere CO₂ exchange. Long-term observations also show that the spatiotemporal patterns of δ¹³C-CO₂ vary interannually, which is mainly related to the impact of climate variability on the terrestrial biosphere. We are actively engaged in using these data in complex modeling frameworks to better understand the inter-relationships between climate and the global carbon cycle.