Abstract

A 160-k.y.-old laminated sediment record from the Santa Barbara Basin, California, analyzed using scanning electron microscope techniques, provides a history of interannual variability of marine production and coastal runoff. We used backscatter electron imagery to measure the components of the varve; these include a terrigenous lamina formed by seasonal runoff from winter rains together with a diatomaceous lamina that records marine production during the spring and early summer. Spectral analysis of terrigenous and diatomaceous laminae thickness reveals significant periodicities of 3.1 and 8.4 yr in the terrigenous series; these are indistinguishable, within the frequency resolution of the spectra, from significant periodicities of 3.5 and 7.6 yr in the diatomaceous series. The 3.1 and 3.5 yr periodicities record El Niño modulation of coastal runoff and marine production; the 8.4 and 7.6 yr periodicities are consistent with modulation by strong to very strong El Niño events. This is supported by the results of cross-spectral analysis of the terrigenous and diatomaceous records, which reveal inverse or antiphase relationships at 3.5 and 7.6 yr. Our work adds to a body of evidence that suggests that El Niño has been a persistent feature of late Quaternary climate variability.

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