Indonesian Throughflow and monsoon activity records in the Timor Sea since the last glacial maximum

Indonesian Throughflow (ITF) is known to play an important role in the heat exchange between the Pacific and the Indian Oceans. However, our understanding of the long-term evolution of the ITF and, in particular, the mechanism of heat transport is limited. Here, we present a high-resolution foraminifera-based multi-proxy study in the main ITF outflow area of the Timor Sea, to reconstruct the ITF variability and to understand the relationship between the ITF changes and monsoon activity from the last glacial maximum (LGM) to the Holocene. Our results show that when the strong surface water ITF occurs, high productivity is related to the mixing of the upper water column owing to the wind-driven upwelling rather than the shoaling of the depth of thermocline (DOT). By contrast, the DOT is affected more strongly by the ITF than by the monsoonal wind-driven upwelling in the Indonesian Seas. During the LGM (23–19 ka) and middle Holocene (8–6 ka), warm surface water ITF was dominated owing to the lowered sea level and (or) the higher steric height difference between the western Pacific and eastern Indian Oceans as a result of the strong southeast monsoon. During the early Holocene (11–8 ka) and late Holocene (last ~ 6 ka), because of the postglacial high sea level, the strong northwest monsoon and heavy rains, large amounts of freshwater flowed into the Java Sea from the South China Sea (SCS). The freshwater plug at the southern tip of the Makassar Strait blocked the warm surface flow, thus initiating the enhanced thermocline ITF. In the Timor Sea, the changes in the vertical profile of the ITF were influenced by the glacio-eustatic sea-level changes that have modified the geometry of the pathways within the Indonesian Seas, as well as by the monsoon activity which was modulated by the changes in the insolation with a precessional cyclicity.