Abstract
Previous studies suggested the multi-millennial scale changes of Australian-Indonesian monsoon (AIM) rainfall, but little is known about their mechanism. Here, AIM rainfall changes since the Last Deglaciation (~18 ka BP) are inferred from geochemical elemental ratios (terrigenous input) and palynological proxies (pollen and spores). Pollen and spores indicate drier Last Deglaciation (before ~11 ka BP) and wetter Holocene climates (after ~11 ka BP). Terrigenous input proxies infer three drier periods (i.e., before ~17, ~15–13.5, and 7–3 ka BP) and three wetter periods (i.e., ~17–15, ~13.5–7, and after ~3 ka BP) which represent the Australian-Indonesian summer monsoon (AISM) rainfall changes. Pollen and spores were highly responsive to temperature changes and showed less sensitivity to rainfall changes due to their wider source area, indicating their incompatibility as rainfall proxy. During the Last Deglaciation, AISM rainfall responded to high latitude climatic events related to the latitudinal shifts of the austral summer ITCZ. Sea level rise, solar activity, and orbitally-induced insolation were most likely the primary driver of AISM rainfall changes during the Holocene, but the driving mechanisms behind the latitudinal shifts of the austral summer ITCZ during this period are not yet understood.
Highlights
Despite its importance to the livelihood of people in the densely populated Southern Indonesia region, Australian-Indonesian monsoon (AIM) rainfall is still poorly understood [1,2]
Throughout the Last Deglaciation, wetter and drier periods on a millennial-scale which corresponded to the high latitude climatic events (i.e., Heinrich Stadial 1, Antarctic Cold Reversal, Bølling-Allerød Interstadial, and Younger Dryas) were inferred [1,8,9,10,14]
The Early Holocene (~11–7 ka Before Present (BP)) was characterized by wetter conditions [6,7,16] while Mid and Late Holocene were marked by the contrast condition between Southern Indonesia [1,5,7,16] and Northern
Summary
Despite its importance to the livelihood of people in the densely populated Southern Indonesia region, Australian-Indonesian monsoon (AIM) rainfall is still poorly understood [1,2]. Past changes is significant to generate robust analogs as the basis to predict and model AIM rainfall future changes [3,4] Previous studies from both marine and non-marine proxies in the AIM region (Southern Indonesia and Northern Australia) suggested millennial – multi-millennial scale changes of AIM during the Last Glacial Maximum (LGM)—Holocene [1,5,6,7,8,9,10]. Throughout the Last Deglaciation, wetter and drier periods on a millennial-scale which corresponded to the high latitude climatic events (i.e., Heinrich Stadial 1, Antarctic Cold Reversal, Bølling-Allerød Interstadial, and Younger Dryas) were inferred [1,8,9,10,14] This indicates the importance of atmospheric-oceanic interhemispheric teleconnection on past AIM changes [1,4,15]. The Early Holocene (~11–7 ka BP) was characterized by wetter conditions [6,7,16] while Mid and Late Holocene were marked by the contrast condition between Southern Indonesia (drier Mid Holocene and wetter Late Holocene) [1,5,7,16] and Northern
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