COMPARABILITY OF RADIOCARBON MEASUREMENTS IN DISSOLVED INORGANIC CARBON OF SEAWATER PRODUCED AT ETH-ZURICH

Radiocarbon observations (Delta C-14) in dissolved inorganic carbon (DIC) of seawater provide useful information about ocean carbon cycling and ocean circulation. To deliver high-quality observations, the Laboratory of Ion Beam Physics (LIP) at ETH-Zurich developed a new simplified method allowing the rapid analysis of radiocarbon in DIC of small seawater samples, which is continually assessed by following internal quality controls. However, a comparison with externally produced C-14 measurements to better establish an equivalency between methods was still missing. Here, we make the first intercomparison with the National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS) facility based on 14 duplicate seawater samples collected in 2020. We also compare with prior deep-water observations from the 1970s to 1990s. The results show a very good agreement in both comparisons. The mean Delta C-14 of 12 duplicate samples measured by LIP and NOSAMS were statistically identical within one sigma uncertainty while two other duplicate samples agreed within two sigma. Based on this small number of duplicate samples, LIP values appear to be slightly lower than the NOSAMS values, but more measurements will be needed for confirmation. We also comment on storage and preservation techniques used in this study, including the freezing of samples collected in foil bags.

Automated summary

The Laboratory of Ion Beam Physics (LIP) at ETH-Zurich has developed a simplified method to rapidly analyze radiocarbon in dissolved inorganic carbon (DIC) of seawater. This method has been assessed by internal quality controls, but a comparison with externally produced C-14 measurements was still missing. In a recent study, LIP made the first intercomparison with the National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS) facility, and the results show a very good agreement between the two methods.