Stable water isotopes in HadCM3: Isotopic signature of El Niño–Southern Oscillation and the tropical amount effect

Abstract

Stable water isotopes have been added to the full hydrological cycle of the Hadley Centre Climate model (HadCM3) coupled atmosphere‐ocean GCM. Simulations of δ18 O in precipitation and at the ocean surface compare well with observations for the present‐day climate. The model has been used to investigate the isotopic anomalies associated with ENSO; it is found that the anomalous δ18 O in precipitation is correlated with the anomalous precipitation amount in accordance with the “amount effect.” The El Niño δ18 O anomaly at the ocean surface is largest in coastal regions because of the mixing of ocean water and the more depleted runoff from the land surface. Coral δ18 O anomalies were estimated, using an established empirical relationship, and generally reflect ocean surface δ18 O anomalies in coastal regions and sea surface temperatures away from the coast. The spatial relationship between tropical precipitation and δ18 O was investigated for the El Niño anomaly simulated by HadCM3. Weighting the El Niño precipitation anomaly by the precipitation amount at each grid box gave a large increase in the spatial correlation between tropical precipitation and δ18 O. This improvement was most apparent over land points and between 10 and 20° of latitude.