Response of the equatorial Pacific to chlorophyll pigment in a mixed layerisopycnal ocean general circulation model

The influence of phytoplankton on the upper ocean dynamics and thermodynami cs in the equatorial Pacific is investigated using isopycnal ocean general circulation model (OPYC) coupled with a mixed layer model and remotely sens ed chlorophyll pigment concentration from the Coastal Zone Color Scanner (C ZCS). In the equatorial Pacific heat accumulation due to a higher abundance of chlorophyll pigments in the equatorial Pacific leads to a decrease of t he mixed layer thickness. This generates anomalous westward geostrophic cur rents north and south of the equator. In the western equatorial Pacific, th ese anomalous geostrophic currents merge into and strengthen the equatorial undercurrent (EUC), supplying water mass from the 200 m depth to the easte rn equatorial Pacific. This chlorophyll-induced response of the undercurren t enhances upwelling around 110W, resulting in a lower sea surf;lct tempera ture (SST) than without chlorophyll. Thus, thermal gradients due to absorpt ion of solar radiation by phytoplankton may contribute remotely to equatori al upwelling in the eastern Pacific.