资源环境科技发展态势分析平台

The drivers of El Nino-Southern Oscillation (ENSO) intensity change during the mid-Holocene (MH) are investigated through employing a coupled model that exhibits excellent performance in simulating the present-day ENSO behaviors. The model shows a 28% decrease in ENSO intensity in the MH simulation compared to the pre-industrial (PI) simulation, showing an agreement with the ranges indicated by the paleo-proxies. Based on quantitative analyses, we reveal that the changes in the oceanic dynamic processes (including the thermocline, zonal-advection, and Ekman feedback terms, in the order from being most to least important) were the major drivers of the reduced ENSO intensity in the MH. Further diagnosis analyses show that the weakening in all three oceanic dynamic terms could be traced back to the weakened thermocline response to zonal wind stress anomaly in the MH compared to that in the PI. Such weakened thermocline response was due to the relatively flattened meridional structure of ENSO-related interannual anomaly field (e.g., zonal wind stress anomaly field) in the MH, which arose from the strengthening of the mean meridional overturning circulation, namely, the mean Pacific subtropical cell (STC). The process-oriented analyses throughout this study suggest a critical linkage between ENSO intensity change and mean STC change in the MH, through documenting how the mean STC change altered the oceanic dynamic processes and thus drove the ENSO intensity change.