Understanding the dynamics of the Indonesian Throughflow and its global significance, both today and in the Late Quaternary

This study investigates the Indonesian Throughflow (ITF), the current connects the Pacific and Indian Ocean via the Indonesian Seas, in both the modern and palaeo climate background. In the contemporary part, the interannual variability of the ITF and the behaviour of the local flows is studied. Using reanalysis dataset, the average ITF volume transport is 12.76 ± 2.74 Sv (106 m3s-1) during 1980 to 2016. The ITF hydrological characteristics support the current understanding of the main water source of the ITF is constructed by the colder and fresher water from the North Pacific and warm and saltier water from the South Pacific. The ENSO affects the ITF transport by the strength and distribution of monsoon on the seasonal scale. A shift of vertical structure of the ITF horizontal transport was found and located at the Banda Sea during the 1990s. The box model results indicate that the water source of the Banda Sea is essential for the stratification: the increased water supply from the South China Sea into the Banda sea would change the stratification of horizontal transport with a prolonged effect and the reanalysis data agrees. The palaeo research focuses long-term, geographically distant influences of the insolation variation and the ITF connection on the global meridional overturning circulation during the deglacial process since the Last Glacial Maximum (LGM). To achieve this, a numerical model, FRUGAL, simulated the natural, insolation varied and closed ITF scenario with LGM boundary. The results suggest that the varying insolation strengthened the polar-tropical temperature and salinity gradient, and caused the strengthening of the Southern Hemisphere Overturning at ~8 ka BP. The variation of the Southern Ocean and sensitive areas is consistent with the insolation variation. The closure of the ITF highly reduced the Atlantic Overturning and weakened the Agulhas Current; the Drake Passage presents a significant response to the closure of ITF; the seasonal variation weakened in Pacific Overturning but strengthened in Southern Hemisphere Overturning.