Orbital-scale Asian monsoon variability and its forcing mechanisms: A new conceptual model

The nature and drivers of orbital-scale Asian monsoon variability remain debated, with different proxy archives (loess, stalagmite δ 18 O, lacustrine and marine records) yielding contradictory spectral signatures and phase relationships. Here, we systematically synthesize representative geological records spanning the past 690 kyr and propose a two-pathway conceptual model (2P model) that reconciles these discrepancies. This model posits that orbital-scale monsoon variability is jointly governed by two main pathways, which together reproduce the principal spectral and phase characteristics observed across diverse geological monsoon archives. The first pathway (P ins ) represents an immediate response to low-latitude summer insolation, while the second pathway (P ice ) responds to high-latitude ice-mediated forcing. Both pathways quickly respond to their respective drivers without significant lag. This framework provides a consistent explanation for the observed ~100-kyr, ~40-kyr, and ~ 20-kyr cycles in most of the monsoon records. The apparent ~2–3-kyr phase lag between Asian stalagmite δ 18 O minima and precession minima arises naturally from the competition between these two differently-phased forcing drivers. Available climate simulations suggest that P ins is primarily controlled by land–sea thermal contrast driven by local insolation, and P ice reflects the influence of ice-mediated boundary conditions including water-holding capacity, sea level, sea surface temperature, and Tibetan Plateau thermal effects. This two-pathway framework reconciles the contrasting spectral signatures among loess, stalagmite, lacustrine and marine records. It also explains the synchronous overprinting of low-latitude and high-latitude signals in monsoon archives, and provides a conceptual basis that can be further tested for future monsoon research and climate modelling efforts.