Phytoplankton Dynamics and Environmental Variability in the Eastern Equatorial Pacific Over Glacial‐Interglacial Timescales

Abstract The Eastern Equatorial Pacific serves as a critical region for understanding the interplay between phytoplankton dynamics and global carbon cycling over glacial‐interglacial timescales. This study investigates the calcareous nannofossils from sediment core MV1014‐02‐17JC (17JC) and previously published diatom assemblage data from core MD02‐2529, correlating their abundances with environmental proxy records for temperature, nutrient availability, and productivity from previously published data obtained from 17JC and nearby core ME‐0005A‐24JC. Coccolithophore abundance data were obtained on a 10 cm sampling interval to observe glacial‐interglacial variability in fossil assemblages. The analysis reveals that coccolithophore species, particularly Gephyrocapsa oceanica and Florisphaera profunda , display significant shifts in dominance corresponding to glacial and interglacial intervals. During interglacial stages, increased stratification and higher sea surface temperatures favor F . profunda , whereas glacial intervals with enhanced upwelling and nutrient availability support G . oceanica . Principal Coordinate Analysis and cluster analysis demonstrate that sea surface temperature (SST), or nutrients that covary with SST, is a primary driver of these assemblage changes, with minor secondary influences from nutrient fluxes. The comparison of primary controls on the calcareous nannofossil and diatom group abundances suggests that the two groups are responding to different primary drivers of change, potentially differing nutrient supply regimes. These findings underscore the complex interactions between phytoplankton communities and their environment, contributing to our understanding of past oceanographic conditions and their implications for future climate scenarios.