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| Titel |
External and internal origins of ENSO modulation revealed by Holocene corals and climate model simulations |
| VerfasserIn |
Helen McGregor, Steven Phipps, Matthew Fischer, Michael Gagan, Laurent Devriendt, Andrew Wittenberg, Colin Woodroffe, Jian-xin Zhao, Jessica Gaudry, David Fink, Allan Chivas |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250149568
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| Publikation (Nr.) |
 EGU/EGU2017-13928.pdf |
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| Zusammenfassung |
| El Niño-Southern Oscillation (ENSO) is the main driver of Earth’s interannual climate
variability. Palaeoclimate records indicate reduced ENSO variance during the middle
Holocene; however, the extent to which external forcing has driven past changes in the
magnitude and characteristics of ENSO are matters of considerable debate. Here, we combine
coral oxygen isotope (δ18O) data from central Pacific corals, with 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 taken into account.
Analysis of the forced simulations reveals that increasing NINO3.4 SST variance arises
from a weakening of the Asian summer monsoon circulation, and an associated
weakening of the Pacific Walker Circulation, in response to decreasing boreal summer
insolation. The picture is less clear on shorter time scales, and we explore further ENSO
multi-decadal variations focusing on the apparent ENSO amplitude minimum at
3,000-5,000 years ago. We combine a 175-year-long coral δ18O ENSO record from a
4,300-year-old coral with new δ18O results from a ∼300-year-long Porites coral microatoll.
Both corals were discovered on Kiritimati (Christmas) Island, an optimal ENSO
‘centre of action’ in the equatorial Pacific, and radiometric dating indicates that
the corals have a 25-year overlap. Together, the unprecedented contiguous ∼450
year-length of the combined results shows interdecadal modulation of ENSO amplitude.
The results provide a robust baseline of intrinsically generated ENSO modulation,
against which to quantify the response of ENSO to past and future external forcings. |
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