Statistical transfer functions relate living planktonic foraminiferal species of the central equatorial Pacific to measured sea surface temperature, integrated primary productivity, and mixed-layer depth. The faunal estimates successfully reconstruct latitudinal patterns observed in both warm (El Ni¿o, February-March 1992) and cool (La Ni¿a, August-September 1992) seasonal settings. Predictions of mixed-layer depth appear to be unbiased by temperature or productivity in our data set but tend to underestimate deep mixed layers. Interactions between productivity and temperature, perhaps through their common influence on respiration and growth rates, bias foraminiferal transfer functions for both properties. Paleoceanographic estimates may be improved by accounting for such biological processes that translate the environment into a faunal response preserved in the geologic record. ¿ 1998 American Geophysical Union