Abundances of 12 species of planktonic foraminifera collected in two plankton tows from the east tropical Atlantic are compared to the chlorophyll content and the temperature of the sea water from which they were collected. As expected from previous work in the tropics, all dominant tropical species occur in greatest abundance within the photic zone. Many species occur in greatest abundances in the seasonal thermocline in association with the maximum chlorophyll concentration, while a few algal symbiont-bearing species occur in greatest abundance in the mixed layer. The •80 measurements of planktonic foraminifera shells from core top sediment samples confirm the vertical stratification within the photic zone that is suggested by the relationship between hydrography and abundances found in the plankton tows and found in the statistical study by Ravelo et al. [ 1990]. Comparison between the measured •80 values of planktonic foraminifera with the predicted •80 profiles of the overlying water column at three core locations indicate that species abundances in the sediment record the seasonally integrated conditions of the photic zone and suggests that the abundance of a species in the sediment depends on whether the preferred ecological conditions of that species may be 1Now at Marine Sciences, Paper number 92PA02092 0883-8305/92/92PA-02092510.00 found within the photic zone of the overlying water column sometime during the year. Species which calcify below the photic zone have only trace relative abundances. Finally, it appears that the total range of •18 0 values of the dominant species approximates the predicted annual •80 of calcite range in the upper 80 m of the water column.

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Abstract. Foraminifer count and multispecies isotopic data from

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El Niño–Southern Oscillation (ENSO) dominates interannual climate variability; thus, understanding its response to climate forcing is critical. ENSO's sensitivity to changing insolation is poorly understood, due to contrasting interpretations of Holocene proxy records. Some records show dampened ENSO during the early to mid‐Holocene, consistent with insolation forcing of ENSO amplitude, but other records emphasize decadal‐centennial fluctuations in ENSO strength, with no clear trend. To clarify Holocene ENSO behavior, we collected proxy data spanning the last ~12 kyr and find relatively low El Niño amplitude during the early to mid‐Holocene. Our data, together with published work, indicate both a long‐term trend in ENSO strength due to June insolation forcing and high‐amplitude decadal‐centennial fluctuations; both behaviors are shown in models. The best supported mechanism for insolation‐driven dampening of ENSO is weakening of the upwelling feedback by insolation‐forced warming/deepening of thermocline source waters. Elucidating the thermocline's role will help predict future ENSO change.