Quantifiying seasonal-scale changes in El Niño southern oscillation for the past millennia
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Date
2012-01-31
Journal Title
Journal ISSN
Volume Title
Publisher
Australian Meteorological & Oceanographic Society
Abstract
The El Niño-Southern Oscillation (ENSO) is the greatest source of interannual climate variability, yet model
forecasts of the response of this system to global warming are inconsistent. The brevity of the instrumental
record and lack of detailed knowledge of ENSO under different background states contribute to the
uncertainty.
Here we present a sequence of Porites coral microatoll !18O records from Kiritimati (Christmas) Island in
the central equatorial Pacific showing ENSO variability during discrete “windows” spaced between 1500
and 6000 years ago (mid- to late Holocene), when background climate conditions were different due to
changes in the Earth’s orbit around the sun.
Our sequence includes a 175-year monthly-resolved microatoll !18O record showing ENSO variability 4,300
thousand years ago. The record shows a 60% reduction in the ENSO variance, a stronger annual cycle that
persisted for the full 175 years of the record, and limited low frequency (multi-decadal) modulation of the
ENSO signal. El Niño events were ‘damped’ during their June-December growth phase, but still phaselocked
to the seasonal cycle. La Niña events were reduced and together ENSO seasonal phasing was likely
similar to that observed during the weak ENSO period of the 1920-1950s.Further, results from corals aged between 1,500 and 2,000 years ago also show reduced ENSO, as well as
changes in the contribution of the annual cycle, El Niño and La Niña events to the overall coral !18O signal.
Our results show fundamental metrics on the seasonal characteristics of ENSO during the altered background
conditions of the mid- to late Holocene. The results suggest that Holocene ENSO responded to changes in
orbital forcing and that there was limited, unforced variability. This may have implications for ENSO under
future global warming conditions.
Description
Keywords
Seasons, Climates, Seasonal variations, Weather, Southern Oscillation, Greenhouse effect, Pacific Ocean, Corals, Quaternary period
Citation
McGregor, H. V., Fischer, M., Gagan, M., Woodroffe, C., Fink, D., Phipps, S., & Zhao, J. (2012). Quantifiying seasonal-scale changes in El Niño southern oscillation for the past millennia. Paper presented at the AMOS 18th National Conference, "connections in climate systems", University of New South Wales, Sydney, 31 Jan - 3 Feb 2012.