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    Biogeosciences

    201703201703

    A 2700-year record of ENSO and PDO variability from the Californian margin based on coccolithophore assemblages and calcification

    Luc Beaufort and Michaël Grelaud

    El Niño Southern Oscillation, Pacific Decadal Oscillation, past climate variability, Santa Barbara Basin, Solar cycles, Centennial climatic variability

    Variability of the COCOC (composite coccolith proxy) during the last 2700 years in Santa Barbara Basin. Bottom left panel shows the COCOC record in red and blue color, the limit between red and blue is a detrended COCOC record by the 1st PC of a SSA (Vautard and Ghill, 1989) and the 2nd PC of a SSA (the embedding dimension is 40) in black dotted line. Top left panel represent the 2nd (red) and 3rd (blue) PC’s of the SSA. The date of each minima (blue text) and maxima (red text) of the 2nd PC are given. Right panels represent the spectral analysis performed with the Multi Taper Method (Thomson, 1982) of the 2nd PC (red in top panel), 3rd PC (blue), and the COCOC record detrended with the 1st PC (red in the bottom panel). The principal period is given in year.

    The El Niño Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO) account for a large part of modern climate variability. Over the last decades, understanding of these modes of climate variability has increased but prediction in the context of global warming has proven difficult because of the lack of pertinent and reproducible paleodata. Here, we infer the dynamics of these oscillations from fossil assemblage and calcification state of coccolithophore in the Californian margin because El Niño has a strong impact on phytoplankton ecology and PDO on the upwelling intensity and hence on the ocean chemistry. Intense Californian upwelling brings water rich in CO2 and poor in carbonate ions and coccolithophores secrete lower calcified coccoliths. Seasonally laminated sediments of the Santa Barbara Basin are used to document ENSO variability and PDO index for the last 2700 years at a temporal resolution of 3 years. The records present the same characteristics as other PDO or ENSO records from the same area spanning the last centuries. We are therefore confident on the value produced here for the last 2.7 millennia. The records show important centennial variability that is equivalent to solar cycles.