Evolution of Eastern Equatorial Pacific Seasonal and Interannual Variability in Response to Orbital Forcing During the Holocene and Eemian From Model Simulations

Abstract

AbstractCharacteristics of the seasonal and interannual sea surface temperature variability in the eastern equatorial Pacific (EEP) over last two interglacials, the Holocene and Eemian, are analyzed using transient climate simulations with the Kiel Climate Model. There is a tendency toward a strengthening of the seasonal as well as the El Niño/Southern Oscillation (ENSO)‐related variability from the early to the late interglacials. The weaker EEP sea surface temperature annual cycle during the early interglacials is mainly a result of insolation‐forced cooling during its warm phase and dynamically induced warming during its cold phase. Enhanced convection over northern South America weakens northeasterlies in the EEP leading to weaker equatorial upwelling, deeper thermocline and subsequent warming in this region. We show that a negative ENSO modulation of the annual cycle operates only on short timescales and does not affect their evolutions on orbital time scales where both ENSO and annual cycle show similar tendencies to increase.