Bispectral Analysis of Nonlinear Couplings Within the Geologic Record of Global Climate Change

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A major finding 15 years ago was that various oceanographic parameters respond to orbital ("Milankovich") forcings in a linear manner. This means that 1) marine sediments faithfully record the frequencies of orbital patterns, shifted only in amplitude and phase; 2) interaction of the several known orbital frequencies results in marine patterns that are the sum of all these frequencies. The P.I. has recently discovered that Pliocene sediments from the eastern equatorial Pacific (DSDP) Site 572) show non-linear couplings to the Milankovich band. This means that the marinere cord shows evidence of: 1) harmonic distortion, i.e. orbital frequency fO is recorded at fO,2fO,3fO, etc,; 2) intermodulation distortion, i.e. various orbital frequencies both add and subtract to give a complex array of frequencies in the marine record. Funds have been awarded to expand this search for non- linear responses. Because commonly used techniques of time series analysis cannot detect anything other than linear response signals, bispectrum analysis and auto regressive moving average models will be explored as alternative techniques. Sensitivity studies will be conducted, and the final techniques will be applied to the analysis of any of several candidate ODP and DSDP records, using delta O18, delta C13, CaCO3, SST, eolian dust of magnetic susceptibility as the parameter to examine for orbital forcings.