The Australian-Indonesian monsoon through time

The Australian-Indonesian monsoon (AIM) is the manifestation of seasonal rainfall change and wind reversal over northern Australia and the Maritime Continent, within a region of extreme land-sea fragmentation. Past AIM variability and change have been related to large, covarying shifts in the boundary conditions such as the atmospheric CO₂, Northern Hemisphere ice sheets, orbital insolation, and sea-level variations. This review synthesizes what is currently known about AIM evolution and mechanisms, emphasizing the Quaternary where proxy evidence, dating control, and modeling experiments are most abundant. We assess how model hierarchies have been used to separate rainfall and circulation responses, diagnose the role of SST pattern changes and inter-hemispheric energy balance, and show whether shelf exposure should be treated as a first-order monsoon control or a modest boundary condition adjustment. We argue that progress now hinges more on explicit quantification of data uncertainty and proxy-aware evaluation, as well as using isotope-enabled transient simulations and proxy system models that compare models to what proxies record rather than to precipitation alone.