Inter-decadal signals during the last millennium (AD 1117-1992) in the varve record of Santa Barbara basin, California

Annual varve thickness (AD 1117-1992) from Santa Barbara basin has been decomposed into orthogonal components using singular spectrum analysis (SSA) to identify and retrieve inter-decadal oscillations. After removing all variability with periods greater than 150 years, leading SSA eigenfunctions (EOFs) identify four oscillatory pairs with periods of ∼100, ∼58, ∼25, and ∼12 years respectively. Based on 2500 simulated series and on two-sided confidence intervals, EOFs 1-7 are significant at the 99% level and EOFs 8-9 are significant at the 90% level. Oscillatory signals retrieved from the marine varves show an abrupt change in frequency and amplitude near AD 1600. The largest contribution to this environmental shift is given by the interdecadal components, especially the ∼25 and the ∼12-year oscillation. The near-AD 1600 change may be related to multi-annual events reported in the stratigraphy of the nearby Santa Monica Basin and in dendrochronological records of the American Southwest.