Interlaboratory comparison of continuous flow analysis (CFA) systems for high-resolution water isotope measurements in ice cores

The continuous flow analysis technique coupled with cavity ring-down spectrometry (CFA-CRDS) provides a method for high-resolution water isotope analysis of ice cores, which is essential for paleoclimatic reconstructions of local temperatures and regional atmospheric circulation. Compared to the traditional discrete method, CFA-CRDS significantly reduces analysis time. However, the effective resolution at which the isotopic signal can be retrieved from continuous measurements is influenced by system-induced mixing, which smooths the isotopic signal, and by measurement noise, which can further limit the resolution of the continuous record, introducing random fluctuations into the instrument’s signal output. This study compares three CFA-CRDS systems developed at Ca’ Foscari University (Venice), the Laboratoire des Sciences du Climat et de l’Environnement (Paris), and the Institut des Géosciences de l’Environnement (Grenoble) for firn core analysis. Continuous results are compared with discrete data to highlight the strengths and limitations of each system. A spectral analysis is also performed to quantify the impact of internal mixing on signal integrity and to determine the frequency limits imposed by measurement noise. These findings establish the effective resolution limits for retrieving isotopic signals from firn cores. Finally, we discuss critical system configurations and procedural optimisations that enhance the accuracy and resolution of water isotope analysis in ice cores.