Dynamics of the Australian–Indonesian monsoon across Termination II: Implications of molecular-biomarker reconstructions from the Timor Sea

• High-resolution vegetation and primary productivity reconstructions over Termination II
• A dramatic expansion of woody plants at the onset of Termination II
• A reduction in monsoon rainfall seasonality during deglacial and interglacial
• SE winter monsoon intensity possibly in phase with boreal winter insolation

Molecular biomarker-derived proxies in a marine sediment core from the eastern Timor Sea have been employed to track changes in the Australian–Indonesian monsoon system over the time period from the penultimate glacial to the last interglacial. The average chain length of n-alkanes originating from terrestrial higher plants reveals an expansion of woody plants during both Termination II and the last interglacial with respect to the penultimate glacial. This is consistent with previous reconstructions for the last glacial–interglacial cycle, indicating that water-stress conditions during dry seasons of southern Indonesia should have been relieved during interglacials and deglacials relative to glacials. However, in contrast to an only muted response during Heinrich Stadial 1, the vegetation composition showed a dramatic and prominent change during Heinrich Stadial 11. This was probably caused by a much more significant and longer duration iceberg discharge event to the northern North Atlantic during Heinrich Stadial 11 relative to Heinrich Stadial 1, which exerted a significant influence on the tropical hydrological cycle and monsoon rainfall seasonality. In addition, marine algae-derived biomarkers are used to reconstruct primary productivity variations, which are in agreement with previous studies from the same area. The precessional cyclicity of paleo-productivity variations is possibly induced by changes in the Australian–Indonesian winter monsoon intensity, showing a correlation with boreal winter insolation. However, this phase relationship is in contrast to the inference based on other lines of evidence, which suggests strong winter monsoon strength during boreal summer insolation maxima. New winter monsoon proxies are therefore required to clarify this discrepancy.