The Australian summer monsoon (ASM) is primarily a synoptic feature determined by the differential thermal response to solar insolation between the Australian continent and the western Pacific warm pool (WPWP) in austral summer. Little is known about the process involved in driving long-term ASM variability. Here we present a 180 ka record of terrestrial fluxes into offshore southeastern Papua New Guinea (PNG), a prevailing monsoon area in the WPWP. Terrestrial fluxes were estimated by a 230Th-normalized method, indicating higher terrestrial inputs into the ocean during glacial stages. We argue that the higher terrestrial fluxes are mainly fluvial, which in turn are linked to stronger ASM precipitation on land, though the increased terrestrial flux could possibly also be due to the lowstand or glacial erosion of mountain glaciers. Cross-spectral analysis indicates that the ASM precipitation maxima are controlled by local summer insolation maxima, WPWP sea-surface temperature minima and East Asian winter monsoon (EAWM) maxima in precession frequency bands (21 ka−1). This result suggests that the 21 ka components of the ASM in the past 180 ka are not only insolation driven but also a dynamic component strengthened by cross-hemispheric pressure gradient resulted from the precession maxima forcing. Copyright © 2012 John Wiley & Sons, Ltd.