The influence of phytoplankton on the upper ocean dynamics and thermodynamics in the equatorial Pacific is investigated using an isopycnal ocean general circulation model (OPYC) coupled with a mixed layer model and remotely sensed chlorophyll pigment concentration from the Coastal Zone Color Scanner (CZCS). In the equatorial Pacific heat accumulation due to a higher abundance of chlorophyll pigments in the equatorial Pacific leads to a decrease of the mixed layer thickness. This generates anomalous westward geostrophic currents north and south of the equator. In the western equatorial Pacific, these anomalous geostrophic currents merge into and strengthen the equatorial undercurrent (EUC), supplying water mass from the 200 m depth to the eastern equatorial Pacific. This chlorophyll-induced response of the undercurrent enhances upwelling around 110W, resulting in a lower sea surface temperature (SST) than without chlorophyll. Thus, thermal gradients due to absorption of solar radiation by phytoplankton may contribute remotely to equatorial upwelling in the eastern Pacific. ¿ 2001 American Geophysical Union