Maintaining consistent traceability in high-precision isotope measurements of CO2: a way to verify atmospheric trends of δ13C and δ18O

[摘要] Maintaining consistent traceability of high-precision measurements ofCO₂ isotopes is critical in order to obtain accurate atmospheric trends ofδ¹³C and δ¹⁸O (in CO₂). Although a number oflaboratories/organizations around the world have been conducting baselinemeasurements of atmospheric CO₂ isotopes for several decades, reportson the traceability and maintenance are rare. In this paper, a principle andan approach for maintaining consistent traceability in high-precisionisotope measurements (δ¹³C and δ¹⁸O) ofatmospheric CO₂ are described. The concept of Big Delta is introduced andits role in maintaining traceability of the isotope measurements isdescribed and discussed extensively. The uncertainties of the traceabilityhave been estimated based on annual calibration records over the last 10 yr.The overall uncertainties of CO₂ isotope measurements forindividual ambient samples analyzed by the program at Environment Canadahave been estimated (excluding these associated with the sampling). Thevalues are 0.02 and 0.05‰ in δ¹³C and δ¹⁸O, respectively, which areclose to the World Meteorological Organization (WMO) targets for data compatibility. The annual rates of change in δ¹³C andδ¹⁸O of the primary anchor (which links the flask measurementsback to the VPDB-CO₂ scale) are close to zero (−0.0016 ± 0.0012‰,and −0.006 ± 0.003‰ peryear, respectively) over a period of 10 yr (2001–2011). The averageannual changes of δ¹³C and δ¹⁸O in air CO₂ atAlert GAW station over the period from 1999 to 2010 have been evaluated andconfirmed; they are −0.025 ± 0.003‰ and0.000 ± 0.010‰, respectively. The results areconsistent with a continuous contribution of fossil fuel CO₂ to theatmosphere, having a trend toward more negative in δ¹³C,whereas the lack of change in δ¹⁸O likely reflects theinfluence from the global hydrologic cycle. The total change of δ¹³Cand δ¹⁸O during this period is ~0.27‰ and~0.00‰, respectively. Finally, the challenges andrecommendations as strategies to maintain a consistent traceability aredescribed.

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