African Monsoonal Precipitation Modulates the Indian Ocean Walker Circulation in the Mid‐Holocene and Last Interglacial

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Abstract Understanding the behavior of the Indian Ocean Walker circulation (IWC) is crucial for interpreting past climate variations; however, its mechanisms during typical interglacial periods remain insufficiently understood. This study examines IWC changes during the mid‐Holocene and Last Interglacial (LIG) periods compared to the preindustrial period using simulations from 16 models within the Coupled Model Intercomparison Project Phase 6 framework. The results reveal a weakened annual‐mean IWC with pronounced seasonal asymmetries. These IWC variations are largely independent of the Pacific Walker circulation and instead arise from Gill‐type adjustments to orbitally driven shifts in African summer monsoonal precipitation. During austral summer, reduced insolation suppresses southern African monsoon precipitation, generating eastward‐propagating Kelvin waves that strengthen the IWC. Conversely, enhanced boreal‐summer insolation intensifies northern African precipitation, producing a mirror‐like response that substantially weakens the IWC and dominates the annual‐mean signal. This summer weakening is additionally fueled by concurrently reduced zonal sea surface temperature (SST) gradients over the tropical Indian Ocean, representing a secondary role of ocean–atmosphere coupling. Additionally, during boreal spring transition, when monsoonal activity is minimal, the IWC undergoes moderate attenuation, and this change is driven by suppressed convection over the Maritime Continent and Southeast Asia, resulting from orbitally induced insolation decline and associated tropical cooling. This study highlights the dominant influence of African monsoonal systems in shaping the IWC during typical interglacial periods rather than regional oceanic conditions, offering a plausible explanation for geological evidence of wetter conditions in eastern Africa and reduced zonal SST gradients in the tropical Indian Ocean.

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