Glacial to Holocene swings of the Australian–Indonesian monsoon

Abstract

The Australian‐Indonesian monsoon is an important component of the climate system in the tropical Indo‐Pacific region 1 . However, its past variability, relation with northern and southern high-latitude climate and connection to the other Asian monsoon systems are poorly understood. Here we present high-resolution records of monsoon-controlled austral winter upwelling during the past 22,000 years, based on planktic foraminiferal oxygen isotopes and faunal composition in a sedimentary archive collected offshore southern Java. We show that glacial‐interglacial variations in the Australian‐Indonesian winter monsoon were in phase with the Indian summer monsoon system, consistent with their modern linkage through cross-equatorial surface winds. Likewise, millennial-scale variability of upwelling shares similar sign and timing with upwelling variability in the Arabian Sea. On the basis of element composition and grain-size distribution as precipitation-sensitive proxies in the same archive, we infer that (austral) summer monsoon rainfall was highest during the Bolling‐Allerod period and the past 2,500 years. Our results indicate drier conditions during Heinrich Stadial 1 due to a southward shift of summer rainfall and a relatively weak Hadley cell south of the Equator. We suggest that the Australian‐Indonesian summer and winter monsoon variability were closely linked to summer insolation and abrupt climate changes in the northern hemisphere. The seasonality of the global monsoon is of central importance to the global hydrologic cycle and its environmental influence on human societies. Palaeoclimate reconstructions generally agree that the strengths of the East Asian monsoon and the Indian monsoon are tightly coupled to the Northern Hemisphere climate through zonal migrations of the monsoon convection centres, also interpreted as Intertropical Convergence Zone (ITCZ) migration 26 . The mechanism of the AustralianIndone