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Multi-Decadal Modes of Pacific Sea Surface Temperature Variability
Dima, M., Felis, T., Lohmann, G. and Rimbu, N.  2005.  Distinct modes of bidecadal and multidecadal variability in a climate reconstruction of the last centuries from a South Pacific coral.  Climate Dynamics 25: 329-336.

What was done
Previous studies of a Rarotonga coral-based sea surface temperature (SST) reconstruction from the Cook Islands, South Pacific Ocean, have focused on documenting and interpreting decadal and interdecadal variability without separating distinct modes of variability within this frequency band (Linsley et al. 2000, 2004; Evans et al. 2001).  In the present study, Dima et al. reanalyze the original coral record using Singular Spectrum Analysis in an effort to determine the dominant periods of multi-decadal variability in the series over the period 1727-1996.

What was learned
Results of the analysis revealed two dominant multi-decadal cycles, with periods of about 25 and 80 years.  These modes of variability were determined to be similar to multi-decadal modes found in the global SST field of Kaplan et al. (1998) for the period 1856-1996.  The ~25-year cycle was found to be associated with the well-known Pacific Decadal Oscillation, whereas the ~80-year cycle was determined to be "almost identical" to a pattern of solar forcing found by Lohmann et al. (2004), which, according to Dima et al., "points to a possible solar origin" of this mode of SST variability.

What it means
The results of this study provide an intriguing glimpse into the cyclical world of oceanic climatic change, demonstrating the existence of two strong multi-decadal modes of SST variability that are clearly natural in origin.  Hence, one must be extremely cautious in interpreting the significance of SST trends over the past several decades; before they can be attributed to anthropogenic activities, they must have these and other known modes of natural variability removed from them.

Evans, M.N., Cane, M.A., Schrag, D.P., Kaplan, A., Linsley, B.K., Villalba, R. and Wellington, G.M.  2001.  Support for tropically-driven Pacific decadal variability based on paleoproxy evidence.  Geophysical Research Letters 28: 3689-3692.

Kaplan, A., Cane, M.A., Kushnir, Y., Clement, A.C., Blumenthal, M.B. and Rajagopalan, B.  1998.  Analyses of global sea surface temperature 1856-1991.  Journal of Geophysical Research 103: 18,567-18,589.

Linsley, B.K., Wellington, G.M. and Schrag, D.P.  2000.  Decadal sea surface temperature variability in the subtropical South Pacific from 1726 to 1997 A.D.  Science 290: 1145-1148.

Linsley, B.K., Wellington, G.M., Schrag, D.P., Ren, L., Salinger, M.J. and Tudhope, A.W.  2004.  Geochemical evidence from corals for changes in the amplitude and spatial pattern of South Pacific interdecadal climate variability over the last 300 years.  Climate Dynamics 22: 1-11.

Lohmann, G., Rimbu, N. and Dima, M.  2004.  Climate signature of solar irradiance variations: analysis of long-term instrumental, historical, and proxy data.  International Journal of Climatology 24: 1045-1056.

Reviewed 4 January 2006