A 2100 year BP record of the Pacific Decadal Oscillation, El Niٌo Southern Oscillation and Quasi-Biennial Oscillation in marine production and fluvial input from Saanich Inlet, British Columbia

Exceptional varved sediments of 2100 years BP recovered from Saanich Inlet have been analysed using high-resolution scanning electron microscopy and spectral analysis techniques. Each varve may contain up to 22 well defined individual laminae which can be attributed to seasonal-scale processes. Sediment flux comprises alternating diatom ooze/diatomaceous mud deposited during spring through autumn and a silty-clay deposited during winter. The latter may be sporadically punctuated by clay-rich laminae. Identification of some 2000 individual consecutive laminae, based on fabric and diatom assemblage, has allowed the construction of time series data for spectral analysis. Laminae types analysed include: early spring Thalassiosira spp., late spring/early summer Skeletonema costatum, multiple summer/autumn Chaetoceros spp. diatom oozes and sporadically present clay-rich winter flood deposits. Sub-decadal periods have been identified and linked to the Quasi-Biennial Oscillation (QBO) and El Niٌo Southern Oscillation (ENSO), and decadal periods to the Pacific Decadal Oscillation (PDO). Comparison of spectral analysis results with modern analogues suggests associations may exist between: early spring Thalassiosira spp. laminae and stronger La Niٌa events; late spring/early summer S. costatum laminae and El Niٌo events; summer/autumn Chaetoceros spp. multiple laminae and negative Pacific Northwest Index (PNI) regimes; and sporadically present winter clay-rich laminae and PNI-regimes. The average period for an ENSO cycle was 3.6 years, QBO 2.5 years and PDO 14.8 years. Spectral analysis of the more recent PNI record shows similar significant periods of 13.2, 3.7 and 2.6 years. Multi-decadal periods recorded include: 42.2 and 31.3 years, which might suggest multiples of PDO.