Calcareous phytoplankton response to the half century of interannual climatic variability in Santa Barbara Basin (California)

A high-resolution study of calcareous phytoplankton in a box core from the Santa Barbara Basin (SBB) reveals floral assemblage fluctuations which can be related to climatic and paleoceanographic changes during the last half century (1940-1996). In particular, Gephyrocapsa oceanica production increased during El Niño periods, in response to high temperatures, silica depletion, and increased iron availability. Conversely, Helicosphaera carteri flux increases in conjunction with lower surface temperatures associated with La Niña episodes. Increasing abundances of Florisphaera profunda and Umbilicosphaera sibogae after 1970 reflect a warming trend and increased stratification within the basin associated with the warm phase of the Pacific Decadal Oscillation (PDO). Conversely, increased abundances of Coccolithus pelagicus and Calcidiscus leptoporus before 1970 mark the cold phase of PDO. These coccolithophore production rate data are consistent with instrumental records of surface and thermocline temperatures monitored since 1950. This is the first study to document the response of calcareous phytoplankton to surface water warming occurring in SBB since 1970.