A TRANSATLANTIC SECTION OF SHIPBOARD DIC CONCENTRATION AND δ13C-DIC MEASUREMENTS AND RESULTS FROM A WORLDWIDE INTER COMPARISON STUDY
I developed and optimized a Cavity Ring-Down Spectroscopy based method for simultaneous determination of dissolved inorganic carbon concentration ([DIC]) and its stable carbon isotope composition (δ13C-DIC) in seawater. The new method was tested on the research vessel Celtic Explorer during an occupation of the Go-Ship A02 trans-Atlantic hydrographic section in 2017. The precision and accuracy for [DIC] determinations achieved ±3 μmol/kg. Precision of δ13C-DIC determination was better than ±0.12‰. Using deep seawater samples (DSW) collected during the cruise and a DIC Reference Material (RM), I organized a worldwide inter comparison experiment for the measurement of δ13C-DIC in seawater samples. Results from 16 participating groups showed excellent agreement (1σ of 0.11‰ and 0.10‰ for RM and DSW respectively). A normalization procedure increased the inter-laboratory precision of the DSW’ δ13C-DIC even further (1σ of 0.05‰). I also give a very brief overview of the δ13C-DIC results from the cruise.