An ocean‐biology‐induced negative feedback on ENSO as derived from a hybrid coupled model of the tropical Pacific

Biological conditions in the tropical Pacific Ocean (e.g., phytoplankton biomass) are strongly regulated by physical changes that are associated with the El Niño‐Southern Oscillation (ENSO). The existence and variation of phytoplankton biomass act to modulate the vertical penetration of the incoming sunlight into the upper ocean, which causes an ocean‐biology‐induced heating (OBH) effect on the climate system. Previously, the penetration depth of solar radiation in the upper ocean (H p ) has been defined to describe the related bioclimate connections. An empirical model for interannual H p variability that is parameterized in terms of its relationship with the sea surface temperature (SST) in the tropical Pacific was derived from remotely sensed ocean color data and is incorporated into a hybrid coupled model (HCM) to represent the OBH effects. In this paper, several HCM experiments are performed to demonstrate the biofeedback onto the ENSO, including a climatological H p run (in which H p is prescribed as only seasonally varying), interannual H p runs (with different intensities of the interannually varying OBH effects), and a run in which the sign of the OBH effect is reversed. Significant modulating impacts on the interannual variability are found in the HCM and are characterized by a negative feedback between the ocean biology and the climate system in the tropical Pacific; stronger the OBH feedback, weaker the interannual variability. The processes that are involved in the feedback are analyzed. The SST is modulated indirectly by dynamic ocean processes that are induced by OBH. The significance and implication of the OBH effects are discussed in terms of their roles in ENSO variability and the model biases in the tropical Pacific.