A Newly Designed Analytical Line to Examine Fluid Inclusion Isotopic Compositions in a Variety of Carbonate Samples

δ 18 O and δD of fluid inclusionsin carbonates provide insights into temperatures and fluid chemical compositions prevailing during the carbonate precipitation, however, various analytical restrictions limit a wider application of this proxy. This paper presents a new fluid inclusionsisotopic analytical line coupled to an online cavity ring‐down spectrometer that increased the analytical productivity up to 10 carbonate samples per working day. This efficiency allowed for the first time to assess the reliability a large set of water samples with size ranging from 0.1 to 1 µL. Good reproducibility (±0.5‰ for δ 18 O and ± 2‰ δD; 1σ) is obtained for water quantity superior or equal to 0.3 μL and no evidence of memory effect is found. The line is further tested using two types of natural carbonates: (1) modern speleothemssamples from caves for which δ 18 O and δD values of drip water were measured and (2) diagenetic carbonates for which the δ 18 O of the parent water were independently back‐calculated from carbonate clumped isotope Δ 47 measurements. Speleothem fluid inclusionvalues despite falling close to the Global Meteoritic Water Line are not always representative of the isotopic composition of the parent drip water. Results on diagenetic cements show that the δ 18 O water values measured in fluid inclusionsagree, within 1%, with the δ 18 O water independently derived from Δ 47 measurements. Overall, this study confirms the reliability and accuracy of the developed analytical line for carbonate fluid inclusionanalyses with a good reproducibility obtained for water quantity above 0.3 μL.