MODELING PLANKTIC FORAMINIFERAL ASSEMBLAGE CHANGES AND APPLICATION TOSEA-SURFACE TEMPERATURE ESTIMATION IN THE WESTERN EQUATORIAL PACIFIC-OCEAN

Calcite dissolution occurring on the sea floor impedes accurate sea su rface temperature estimates from planktic foraminiferal assemblage com positions. As an attempt to address this issue, we devised a mathemati cal model to study the progressive modifications of species compositio ns by dissolution and to account for its effect on temperature estimat es. To calibrate the model, planktic foraminiferal compositions and pr eservation were examined for a bathymetric transect of samples from th e Ontong Java Plateau in the western equatorial Pacific Ocean; Along t he transect, variations in relative abundances of various species show depth-related patterns, and the preservation of foraminifera decrease s with water depth. Assuming that the population of each foraminiferal species has a bell-shaped response curve to dissolution, the model nu merically dissolves the well-preserved shallowest sample to the levels that are indicated by the fragmentation levels of the samples from de eper water depths. Our results show that the model reproduces the obse rved depth-related abundance variation patterns with remarkable accura cy. After calibration, the model is able to reconstruct the original s pecies compositions for the samples from water depths above 3500 m by numerically adding back what has been dissolved. This reduces the effe ct of dissolution on the sea surface temperature estimates from about 2 degrees C to about 0.5 degrees C for these samples. We observed that the more dissolved samples on the Ontong Java Plateau give higher sea surface temperature estimates, a pattern opposite to what is observed in the South China Sea. We attribute the differing effects of dissolu tion on temperature estimates to regional differences in foraminiferal faunal compositions.