OF-CEAS laser spectroscopy to measure water isotopes in dry environments: example of application in Antarctica

Abstract. Water vapour isotopes are important tools to better understand processes governing the atmospheric hydrological cycle. Their measurement in polar regions is crucial to improve the interpretation of water isotopic records in ice cores. In situ water vapour isotopic monitoring is however an important challenge, especially in dry places of the East Antarctic plateau where water mixing ratio can be as low as 10 ppmv. We present in this article new commercial laser spectrometers based on the optical feedback – cavity enhanced absorption spectroscopy (OF-CEAS) technique, adapted for water vapour isotopic measurement in dry regions. We characterize a first instrument adapted for Antarctic coastal monitoring with an optical cavity finesse of 64,000 (ringdown time of 54 µs), installed at Dumont d’Urville station during the summer campaign 2022–2023, and a second instrument with a high finesse of 116,000 (98 µs ringdown), to be deployed inland East Antarctica. The high finesse instrument demonstrates a stability up to two days of acquisition, with a limit of detection down to 10 ppmv humidity for 𝛿D and 100 ppmv for 𝛿¹⁸O.