The effects of El Nino Events on Coccolithophore assemblages in the Santa Barbara Basin (California)

El Niño (EN) is a disruption of the ocean-atmosphere system in the tropical Pacific that has important consequences for global weather patterns. EN events are marked by years with an increase of sea-surface temperature, sea-level barometric pressure and rain fall along the California Margin. A laminated box core from the Santa Barbara anoxic Basin is used in this work to study the EN effect on primary productivity, in particular on coccolithophores in the California Borderland during the last 60 years. The EN events were defined by two indexes: Multivariate ENSO Index (MEI) from 1996 to 1950 and Southern Oscillation Index (SOI) from 1950 to 1939. In the box-core samples we can observe an increase of coccolithophore carbonate flux during the years following EN events (positive MEI and negative SOI). In particular, Gepyrocapsa oceanica flux abundance shows a strong positive correlation with strong EN events, like in 1965-66, 1982-83 and in 1997-98 (for 1997-98 from sediment trap experiment in the center of SBB). Significant sea-cliff erosion and storm damage occurred along the central coast of California during the 1982-83 and 1997-98 El Nino winters. We will discuss the coccolithophore response to El Nino events, also considering the minor chemical elemental changes in the surface water column. In our study, it appears that the main oceanographic parameter controlling the distribution of coccolithophore assemblages is temperature, since nitrate and phosphate are relatively high throughout the study period.