Paleoclimatic reconstruction and evaluation of sub-centennial climate variability in the late Holocene using records from massive corals (New Caledonia), tree-rings (New Mexico) and speleothems (China).

摘要

This study focuses on how the construction of a paleoclimate time series influences the interpretation in the frequency domain. Three time series are examined: a New Caledonian coral (Amedee Island), a Chinese speleothem (Dongge Cave), and New Mexican trees (El Malpais).;This study presents a monthly resolved coral Sr/Ca time series from New Caledonia that reconstructs sea surface temperature (SST; 1648--1999). The chronology is based on annual density-band counting, cross-correlating coral Sr/Ca, and 230Th dating. The intracolony coral Sr/Ca variations are coherent on interannual to centennial time scales and are reproducible for >300 years. The SST reconstruction reveals a cooling trend (∼0.4°C) from 1741 to 1815, a colder nineteenth century (∼0.6°C), and a warming trend (∼0.6°C) in the twentieth century. Spectral and wavelet analysis reveals significant inter-decadal periodicities (∼14--21 years/cycle) that modulate with time, and nearly persistent multi-decadal periodicities (∼25--33 years/cycle) that do not exhibit coherence with the Inter-decadal Pacific Oscillation. The multi-decadal periodicities may be a harmonic of the inter-decadal periodicities or may represent an independent mode not previously recognized.;The Dongge Cave time series is based on uneven time intervals between data points (Deltat) requiring interpolation to a constant Deltat for analysis with traditional spectral methods. A comparison of the even and uneven Deltat spectra using the Lomb-Scargle transform reveals the interpolated spectrum contains suppressed periodicities (20 years/cycle), in contrast to the uninterpolated spectrum, resulting in a steeper slope in the red noise model thus influencing significance testing.;The El Malpais time series is an average of tree-ring width series in which the number of series varies with time. Spectral analysis of the entire time series identified significant periodicities. However, significance varies between three temporal subsets, in which the number of series varies; therefore, these periodicities may be a function of the number of series or may represent a real temporal variability. Cross-spectral analysis of the El Malpais and Dongge Cave time series reveals significant coherence; however, cross-wavelet analysis, which examines localized frequencies in the time domain, reveals a lack of correlation; therefore, coherence in the frequency domain does not indicate correlation in the time domain.