Millennial to seasonal scale views of El Niño-Southern Oscillation from central Pacific corals

El Niño-Southern Oscillation (ENSO) is naturally highly variable on interannual to decadal scales making it difficult to detect a possible response to climate forcing. Despite the high variability, several lines of evidence from tropical corals, mollusc, lake sediments, and foraminifera suggest that 5,000-3,000 years ago ENSO variance was on average reduced by 60-80% compared to the present day. We investigate the seasonal-to-centennial variation in ENSO amplitude and tropical climate during this ENSO ‘quiet period’ 5,000-3,000 years ago using a new Sr/Ca SST record from a 175-year-long 4,300-year-old coral, and new d18O and Sr/Ca results from a similar-aged ~180-year-long Porites sp. coral. Both corals were discovered on Kiritimati (Christmas) Island, an optimal ENSO ‘centre of action’ in the central tropical Pacific. Together, these corals confirm a reduction in ENSO amplitude and that ENSO amplitude is modulated on multi-decadal scales. Composites of month-by-month changes in Sr/Ca-SST show an unprecedented view of ENSO and detail which seasonal-scale features of ENSO are an inherent part of the system, and which are subject to change under altered climate states. We also investigate the millennial timescale changes in ENSO variance using combine coral oxygen isotope (18O) data from central Pacific corals and a suite of forced and unforced simulations conducted using the CSIRO Mk3L and GFDL CM2.1 climate system models. On millennial timescales, the coral data reveal a statistically significant increase in ENSO variance over the past 6,000 years. This trend is not reproduced by the unforced model simulations but can be reproduced once orbital forcing is accounted for. Together these views of past ENSO may contribute to advances in understanding the response of ENSO to future changes in climate forcings.
Southern Oscillation, Pacific Ocean, Corals, Climates, Lakes, Sediments, Islands
McGregor, H., Wilcox, P., Fischer, M., Phipps, S., Gagan, M., Wittenberg, A., Felis, T., Kölling, M., Wong, H., Devriendt, L., Woodroffe C., Zhao, J.-X., Fink, D., Gaudry, J., & Chivas, A. (2022). Millennial to seasonal scale views of El Niño-Southern Oscillation from central Pacific corals. Paper presented to AQUA 2022 Conference, 6-8 December 2022, Adelaide. (pp. 73-74). Retrieved from: