Identifying Oxygen Isotopic Signatures of ENSO Dynamics Through Isotope-Enabled Regional Ocean Modeling

Abstract:

Coral oxygen isotope (δ¹⁸O) records provide important constraints on past variability in the El Nino/Southern Oscillation (ENSO). However, the relationship between ENSO activity and δ¹⁸O anomalies is subject to a high degree of uncertainty owing to both observational limitations and poorly understood dynamical processes. The isotope-enabled Regional Ocean Modeling System (isoROMS) is designed to address some of these uncertainties; isoROMS is a flexible modeling framework capable of simulating δ¹⁸O over an arbitrary domain at a variety of spatial resolutions. Initial results for isoROMS simulations at the central equatorial Pacific Line Islands chain over the 1979-2009 period are presented, using water isotopologue fluxes taken from the isotope-enabled NCAR Community Atmosphere Model (iCAM). Mesoscale ocean processes can significantly impact temperature and seawater δ¹⁸O variability under certain conditions, particularly during strong La Nina events. The variability in the ENSO/δ¹⁸O relationship is then investigated over the 20th century using a suite of isoROMS simulations conducted with combinations of atmosphere and ocean reanalysis products, in an effort to determine the optimal form of 'forward models' for predicting δ¹⁸O given local conditions. Implications for our ability to quantitatively reconstruct ENSO amplitude and the properties of El Nino/La Nina events are discussed.