ENSO and decadal climate variability within and between climate regimes : evidence from geochemical analysis of annually-banded massive corals in Papua New Guinea
Alexander W. Tudhope*1, Colin P. Chilcott*1, Graham B. Shimmield*2, Malcolm T. McCulloch*3, Rob Ellam*4 and John Chappell*3
*1 Department of Geology & Geophysics, Edinburgh University
*2 Dunstaffnage Marine Laboratory
*3 Research School of Earth Sciences, Australian National University
*4 Scottish Universities Research & Reactor Centre
Geochemical analysis of the skeletons of annually-banded massive corals can yield multicentury, monthly-resolution proxy records of SST and SSS. Such records can contribute to the understanding of interannual-centennial climate variability by extending the instrumental record and by revealing the sensitivities of different modes of climate variability to changes in global climatic boundary conditions. These roles will be illustrated using examples from living and ancient corals from the north coast of Papua New Guinea where ENSO-related climate variability is recorded in the stable oxygen isotopic and strontium content of the coral skeletons.
MODERN CORALS : Two 110 year long coral records display interdecadal changes in the strength and periodicity of ENSO climate variations over the last century, consistent with and extending existing knowledge. In addition, they indicate significant (0.5-1.0 permil) interdecadal variations in SSS and a trend towards lower SSS through time. This suggests changes in the regional evaporation-precipitation balance and / or changes in fresh-water storage in the Warm Pool.
'INTERGLACIAL' CLIMATE REGIMES : Two multidecadal coral records from 2.5ka and 2.7ka BP and two records from the last interglacial (periods when global climate was similar to, or slightly warmer than present) all show evidence for interannual climate variability in the ENSO waveband. In general, these variations are similar to, or weaker than ENSO cycles of the 20th century.
'GLACIAL' CLIMATE REGIMES : A 70-year long record from a 130ka BP coral which grew when polar ice sheets were expanded and global sea-level was about 80m lower than present also displays ENSO-style climate variability. The frequency, amplitude and interdecadal variability in this palaeo-ENSO signal is strongly reminiscent of patterns seen in modern coral and instrumental records. These results indicate that ENSO may be a persistent component of the tropical climate system, even during periods of significantly reduced regional and global SST.
