Investigating the Forcing and Response in Proxy Records of Multi-Decadal Scale Climate Variability

Multi-decadal climate variability has been detected in both instrumental and proxy climate records and these climate modes have been linked to internal interactions in the climate system, changes in solar irradiance, and episodes of explosive volcanism. We are interested in investigating the links in multi-decadal scale variability between highly resolved proxy records (e.g., tree-rings, speleothems, corals, and lake sediments) and those observed in solar output records. We first investigated the ~2000 year El Malpais (New Mexico) tree-ring record [Grissino-Mayer, 1996] and the late Holocene section of the Dongge Cave (China) speleothem record [Wang et al., 2005]. The El Malpais record contains significant (95% level) concentrations of variance at four periods (~25, ~37, ~57, and ~76 yrs); however, further examination of three temporal subsets found these periodicities varied between subsets. The ~25 yr cycle, which is observed in the PDO, is present in the youngest and oldest subsets. The ~37 and ~54 yr cycles are present in a single subset; the other subsets lack spectral power at these periods. The ~76 yr cycle, which is ~Gleissberg sunspot cycle, is present in the two youngest and most replicated subsets. The chronology of the Dongge record is based on uneven time increments and interpolation was used to generate time series with a constant time increment. Spectral results using the interpolated record tended to suppress periodicities ≤decadal in comparison to the Lomb-Scargle spectrum, which evaluates the spectrum of uneven time series. Robust periodicities at ~23 and ~74 yrs were identified in the Dongge record, which are ~ the PDO and the Gleissberg cycle. Cross-spectral analysis of the El Malpais and Dongge records did not find significant coherence.