Modelling water isotopologues ( 1H 2H 16O, 1H 217O) in the coupled numerical climate model iLOVECLIM (version 1.1.5)

Extier, Thomas; Caley, Thibaut; Roche, Didier M.

Stable water isotopes are used to infer changes in the hydrological cycle for different climate periods and various climatic archives. Following previous developments of inline-formulaδ18O in the coupled climate model of intermediate complexity, iLOVECLIM, we present here the implementation of the inline-formula1Hinline-formula2Hinline-formula16O and inline-formula1Hinline-formula2inline-formula17O water isotopes in the different components of this model and calculate the associated secondary markers deuterium excess (d-excess) and oxygen-17 excess (inline-formula17O-excess) in the atmosphere and ocean. So far, the latter has only been modelled by the atmospheric model LMDZ4. Results of a 5000-year equilibrium simulation under preindustrial conditions are analysed and compared to observations and several isotope-enabled models for the atmosphere and ocean components.

In the atmospheric component, the model correctly reproduces the first-order global distribution of the inline-formulaδ2H and d-excess as observed in the data (inline-formulaR=0.56 for inline-formulaδ2H and 0.36 for d-excess), even if local differences are observed. The model–data correlation is within the range of other water-isotope-enabled general circulation models. The main isotopic effects and the latitudinal gradient are properly modelled, similarly to previous water-isotope-enabled general circulation model simulations, despite a simplified atmospheric component in iLOVECLIM. One exception is observed in Antarctica where the model does not correctly estimate the water isotope composition, a consequence of the non-conservative behaviour of the advection scheme at a very low moisture content. The modelled inline-formula17O-excess presents a too-important dispersion of the values in comparison to the observations and is not correctly reproduced in the model, mainly because of the complex processes involved in the inline-formula17O-excess isotopic value. For the ocean, the model simulates an adequate isotopic ratio in comparison to the observations, except for local areas such as the surface of the Arabian Sea, a part of the Arctic and the western equatorial Indian Ocean. Data–model evaluation also presents a good match for the inline-formulaδ2H over the entire water column in the Atlantic Ocean, reflecting the influence of the different water masses.

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Extier, Thomas / Caley, Thibaut / Roche, Didier M.: Modelling water isotopologues (1H2H16O, 1H217O) in the coupled numerical climate model iLOVECLIM (version 1.1.5). 2024. Copernicus Publications.

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