Earth’s interannual climate variability is dominated by El Niño/Southern Oscillation (ENSO). Palaeoclimate records indicate a lower ENSO variance during the middle Holocene compared with today; however, model simulations have not reproduced the full magnitude of the changes, and whether external forcing drives large intrinsic ENSO variability is therefore a matter of considerable debate. Here we present a 175-year-long, monthly resolved oxygen isotope record, obtained from a Porites coral microatoll located on Kiritimati (Christmas) Island, in the NINO3.4 region of the central equatorial Pacific. Our quantitative record of ENSO variability about 4,300 years ago shows that ENSO variance was persistently reduced by 79%, compared with today, and it exhibits a dominant annual cycle. Season-specific analysis shows that El Niño events were damped during their September–November growth phase, and delayed relative to the climatological year. We suggest that the higher boreal summer insolation at the time strengthened the tropical Pacific zonal winds as well as the gradients in sea surface temperature, and thereby led to an enhanced annual cycle and suppressed ENSO. As the weak ENSO is subject to interdecadal amplitude modulation, we conclude that amplitude modulation is likely to remain robust under altered climates. Our findings show that ENSO is capable of responding to external forcing.

Item Type:	Refereed Article
Keywords:	palaeoclimate, El Nino-Southern Oscillation, Holocene, corals, isotopes, Kiribati
Research Division:	Earth Sciences
Research Group:	Physical Geography and Environmental Geoscience
Research Field:	Palaeoclimatology
Objective Division:	Environment
Objective Group:	Climate and Climate Change
Objective Field:	Climate Variability (excl. Social Impacts)
UTAS Author:	Phipps, SJ (Dr Steven Phipps)
ID Code:	104728
Year Published:	2013
Web of Science® Times Cited:	54
Deposited By:	IMAS Research and Education Centre
Deposited On:	2015-11-18
Last Modified:	2017-10-30
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