Inter-annual tropical Pacific climate variability in an isotope-enabled CGCM: implications for interpreting coral stable oxygen isotope records of ENSO

Water isotope-enabled coupled atmosphere-ocean climate models allow for exploration of the relative contributions to coral stable oxygen isotope (delta O-18(coral)) variability arising from sea surface temperature (SST) and the isotopic composition of seawater (delta O-18(sw)). The unforced behaviour of the isotope-enabled HadCM3 coupled general circulation model suggests that the extent to which inter-annual delta O-18(sw) variability contributes to that in model delta O-18(coral) is strongly spatially dependent, ranging from being negligible in the eastern equatorial Pacific to accounting for 50% of delta O-18(coral) variance in parts of the western Pacific. In these latter cases, a significant component of the inter-annual delta O-18(sw) variability is correlated to that in SST, meaning that local calibrations of the effective local delta O-18(coral)-SST relationships are likely to be essential. Furthermore, the relationship between delta O-18(sw) and SST can be non-linear, such that the model interpretation of central and western equatorial Pacific delta O-18(coral) in the context of a linear dependence on SST alone leads to overestimation (by up to 20 %) of the SST anomalies associated with large El Nino events. Intra-model evaluation of a salinity-based pseudo-coral approach shows that such an approach captures the first-order features of the model delta O-18(sw) behaviour. However, the utility of the pseudo-corals is limited by the extent of spatial variability seen within the modelled slopes of the temporal salinity-delta O-18(sw) relationship.