Water isotope variations in the global ocean model MPI-OM

Abstract

The stable water isotopes H₂¹⁸O and HDO are incorporated as passive tracers into the oceanic general circulation model MPI-OM, and a control simulation under present-day climate conditions is analyzed in detail. Both &delta;¹⁸O and &delta;D distributions at the ocean surface and deep ocean are generally consistent with available observations on the large scale. The modelled &delta;D-&delta; ¹⁸O relations in surface waters slightly deviates from the slope of the global meteoric water line in most basins, and a much steeper slope is detected in Arctic Oceans. The simulated deuterium excess of ocean surface waters shows small variations between 80° S and 55° N, and a strong decrease north of 55° N. The model is also able to capture the quasi-linear relationship between &delta;¹⁸O and salinity <i>S</i>, as well as &delta;D and <i>S</i>, as seen in observational data. Both in the model results and observations, the surface &delta;−<i>S</i> relations show a steeper slope in extra-tropical regions than in tropical regions, which indicates relatively more addition of isotopically depleted water at high latitudes.