NOAA/WDS Paleoclimatology - Muna Composite d18O Record from 1668-2005 CE

We present an annual resolution oxygen isotope anomaly record (Dd18Oc ) record, derived from eight teak (Tectona grandis L.f.) tree ring-dated d18Oc records from Muna, Southeast Sulawesi, Indonesia (5.3?S, 123?E), to investigate the response of El Nino-Southern Oscillation (ENSO) to external radiative forcings (ERF), 1668-2005. The record is significantly correlated (r = 0.41, edf=82, p < 0.001) with the Oct-Sep averaged Nino3.4 SST index for the period 1856-2005, confirming prior results from proxy system (forward) isotopic modeling of the ?d18Oc record as an ENSO indicator. We examined the response of the Dd18Oc record response to established greenhouse gas, volcanic and solar radiative forcing. For the volcanic forcing, we find a significant composite tendency towards ENSO warm phase events in the year following volcanic eruptions, n=29 events, p=0.05. We found no statistically significant changes arising from solar activity, 1751-2005, nor a change in ENSO event distribution, 1681-2005. The latter result suggests either a weak response in ENSO behavior despite known and substantial changes in well-mixed greenhouse gas forcing over the past three centuries, and/or a weak forced signature is not yet emergent given substantial observational uncertainty. These findings are consistent with those found by Cook and Cane (2024), but contrast with some model projections of significantly increased ENSO variability under recent anthropogenic forcing.