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 δ 18 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 δ 18 O in precipitation is correlated with the anomalous precipitation amount in accordance with the "amount effect." The El Nino δ 18 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 δ 18 O anomalies were estimated, using an established empirical relationship, and generally reflect ocean surface δ 18 O anomalies in coastal regions and sea surface temperatures away from the coast. The spatial relationship between tropical precipitation and δ 18 O was investigated for the El Nino anomaly simulated by HadCM3. Weighting the El Nino precipitation anomaly by the precipitation amount at each grid box gave a large increase in the spatial correlation between tropical precipitation and δ 18 O. This improvement was most apparent over land points and between 10 and 20° of latitude. © 2009 by the American Geophysical Union.