Planktonic foraminifieral response to the 1997-1998 El Nino: A sediment-trap record from the Santa Barbara Basin

摘要

Here we report results on a sediment-trap study from the Santa Barbara Basin in which we examine the response of planktonic foraminifera to El Nino conditions. Planktonic foraminifera census counts were performed on biweekly sediment-trap samples collected over the interval spanning late summer 1995 through early spring 1998, a period that captured the transition from "normal" conditions in 1996 to full El Nino conditions during early 1997 through early 1998. Intra-annual variations in the foraminifera assemblage reflect changes in seasonal climate variability, significant differences occurring in both foraminiferal relative abundance and flux values between non-El Nino and El Nino years. Warmer waters in the basin during late 1997 were reflected by a significantly increased presence of warmer-water species generally absent under normal conditions. Surprisingly, despite greatly reduced upwelling conditions, foraminiferal flux values during the spring 1997 upwelling season were more than four times greater than the year before. The contrast between normal and El Nino foraminifer populations has important implications for reconstructing the past history of both El Nino events and more general climate histories from the Santa Barbara Basin varved sediment record.