Summary
Monitoring CO2 isotopes at Cape Grim commenced in 1976 (Goodman, 1980), using CO2 extracted from the air and returned to Aspendale for mass spectrometer analysis. The objective was to distinguish between terrestrial (including biosphere exchanges, deforestation and fossil fuel emissions) and oceanic (physical and biological) exchanges of CO2 with the atmosphere. There are a number of major experimental milestones: · 1982: Upgrade of the Cape Grim in situ glass extraction line (with marked improvement in the quality of d13C measurements). · 1984: Introduction of parallel 5 litre flask collections from a global network, for CO2 extraction (using a duplicate glass extraction line) and analysis at Aspendale. · 1989-92: Change from a VG602D mass spectrometer plus glass extraction system at Aspendale, to a MAT252 with commercial automated miniaturised metal CO2 extraction system. Introduction of 0.5L flask sampling and improved multi-species analyses (in GASLAB) from an expanded global network. · 1992: Introduction of air reference cylinders so that isotopic values in flask air samples are referenced to bracketing extractions and analysis of an air reference rather than the pure-CO2 reference used for Cape Grim ‘in situ’ samples. · 1994: Significant modification to the MAT252 cryogenic extraction line to permit ice core analyses · 1997: Significant modification to the MAT252 mass spectrometer by supplier to overcome long-standing sample-reference cross contamination effect. · 2000: Start construction of an automated in situ extraction line for Cape Grim to permit air reference for the in situ program. Three major challenges have emerged for the Cape Grim d13C record: 1. Major discrepancies are evident between the two-decade Cape Grim time series and the only comparable series from the pioneering Scripps Institution of Oceanography (SIO) program [Keeling et al., 1995; Francey