In situ carbon and oxygen isotopes measurements in carbonates by fiber coupled laser diode-induced calcination: A step towards field isotopic characterization

Natural stable isotopes ratios (δ13Ccarb and δ18Ocarb) of carbonates archived in the geological record are routinely used to reconstruct local global paleo temperatures secular evolution biogeochemical carbon cycle. The state-of-the-art technique, employed since mid 20th century, measure these isotopic starts with field sampling followed by several steps physical chemical laboratory preparation including: (i) microdrilling and/or sawing crushing, (ii) CO2 release wet acid digestion, (iii) gas equilibration, purification transfer, before (iv) phase IRMS measurements. While time resource consuming, they provide accurate measurements δ13Ccarb, δ18Ocarb carbonate contents. This study presents a new protocol involving compact modernized laser calcination system that decreases drastically analyses reducing number preparations together offering possibility performing spatially resolved analysis at mm scale. method is based on use fiber coupled diode device emitting 30 W near infrared 880 nm. energy provided source induces decomposition calcium into lime dioxide. In this work, was collected sample tubes under controlled atmosphere for offline analysis, however additional developments should permit online future. We analyzed 9 different types minerals encompassing range compositions VPDB between +3.3 − 18.2‰ −1.7 14.6‰ δ13Ccarb δ18Ocarb, respectively. A comparison results performed zones both classic methods (micro-drilling digestion) calcination. cross-calibration exercise shows direct positive co-variation correlation coefficient 0.99 regression slope 1 within uncertainties values. values also compared well 0.96, suggesting constant gas-solid equilibrium dioxide lime. reproducibility our replicate dolomite, siderite malachite 1σ standard deviation 0.31 0.77 These reproducibilities observed natural inhomogeneity samples (up 1.3 0.57‰ respectively) as assessed digestion. Based suit study, we demonstrate enables reproducible C O characterization carbonates, effects during do not introduce any fractionation accompanied offset over mineral matrices. findings pave way possibilities δ13C δ18O directly using rapid, portable, easy manipulate devices paired CRDS/IRIS optical-mass spectrometers.