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 13C-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 13C-CO2 of approximately -0.75 over the last three decades, a robust and traceable method is required to track the long-term change in 13C-CO2globally. The Stable Isotope Lab at the INSTAAR of the University of Colorado Boulder has been partnering with NOAAs 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 13C-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 13C-CO2 from more than 70 sites worldwide. The data reveal distinct seasonal variations of 13C-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 13C-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.