Contrasting Isotopic Signatures of Recent Extreme El Nino Events

The El Nino/Southern Oscillation (ENSO) drives the majority of interannual climate variability, and is expected to be strongly influenced by anthropogenic climate change. However, the long timescales of internal ENSO modulation require that paleoclimate information be used in order to create a sufficiently long observational baseline to ensure robust ENSO statistics. Previous work using coral oxygen isotopic records (δ¹⁸O) indicates that ENSO variability may be increasing, but the role of external forcing remains unclear - as do potential contributions from changes to hydrological influences on δ¹⁸O. Here we present results from the isotope-enabled Regional Ocean Modeling System (isoROMS), combined with physical oceanographic and water oxygen isotopic information collected from the central equatorial Pacific during the 2015-16 extreme El Nino. isoROMS provides a spatially and temporally complete dataset, which can be used to understand dynamical differences between the 2015-16 El Nino and other extreme El Nino events during the observational period. This allows us to construct δ¹⁸O-based metrics associated with extreme El Nino events, and to quantify the mechanisms for differences among δ¹⁸O signatures. This work has significant implications for reconstructing past changes to ENSO dynamics and the associated hydrological impacts.