Modelling the water isotope distribution in the Mediterranean Sea using a high-resolution oceanic model (NEMO-MED12-watiso v1.0): evaluation of model results against in situ observations

Stable water isotopes (δ 18 O w and δD w ) have been successfully implemented for the first time in a high-resolution model of the Mediterranean Sea (NEMO-MED12). In this numerical study, model results are compared with available in situ observations to evaluate the model performance of the present-day distribution of stable water isotopes and their relationship with salinity on a subbasin scale. There is good agreement between the modelled and observed distributions of δ 18 O w in the surface water. The model successfully simulates the observed east-west gradient of δ 18 O w characterising surface, intermediate, and deep waters. The results also show good agreement between the simulated δD w and the in situ data. The δD w shows a strong linear relationship with δ 18 O w (r 2 = 0.98) and salinity (r 2 = 0.94) for the whole Mediterranean Sea. Moreover, the modelled relationships between δ 18 O w and salinity agree well with observations, with a weaker slope in the eastern basin than in the western basin. We investigate the relationship of the isotopic signature of the planktonic foraminifera shells (δ 18 O c ) with temperature and the influence of seasonality. Our results suggest a more quantitative use of δ 18 O records, combining reconstruction with modelling approaches.