Records Of Monsoon And Indonesian Cross-flow Activity Since The Mid-Pleistocene In The East Timor Sea

The area of tropical sea is an important source area for global water vapor and heat transfer.The Timor Sea is located in the Indo-Pacific Warm Pool and is the main path of outflow of Indonesian Throughflow(ITF).And it is affected by monsoon,migration of the Intertropical Convergence Zone(ITCZ)and ITF.The sediment records of core MD98-2172 located in the eastern Timor Sea within the main outflow passages of ITF were studied.We analyzed the difference in carbon isotopes between planktonic and benthic foraminifera,and organic carbon content,and the temperature difference of the surface water and thermocline water based on Mg/Ca value conversion of planktonic foraminifer Globigerinoider ruber and Pulleniatia obliquiloculata.We reconstructed the changes of paleo-productivity and thermocline depth and salinity on a longer time scale,and discussed the impact of monsoon and ITF activity the last 380 ka in the eastern Timor Sea.Combined with spectrum analysis,we explored the main driving mechanism of ITF activity.The paleo-productivity proxies of core MD98-2172 show a strong glacial-interglacial contrast,indicating high surface productivity during glacial periods alternating with low productivity during interglacial intervals.When the southern hemisphere summer(December)is at high sunshine,the NW monsoon will be strengthened by the sunshine,resulting in a stronger upwelling activity and shallow thermocline and high paleoproductivity.The depth of the thermocline in the eastern Timor Sea is controlled by ITF activities on the glacial-interglacial scale.When the sea level declines during the glacial periods,the thermocline is dominated by surface water ITF activity,and the thermocline layer is deeper.During the interglacial period,sea level rises and the thermocline ITF activity increases,causing the thermocline to become shallow.A comparison between the remaining seawater oxygen isotopes and the summer sunshine in the southern hemisphere found that the change in surface water salinity in the eastern Timor Sea area is not affected by monsoon activity,and the salinity index cannot reflect the ITF activity affected by monsoon.The thermocline depth(?T)can reflect the influence of the monsoon on ITF activities to a certain extent.During high summer sunshine in the southern hemisphere,the NW monsoon is strong,and a large amount of precipitation forms a freshwater plug in the Makassar Strait,and ITF activity in surface water is suppressed.The increase in thermocline ITF activity results in a shallow thermocline in the Eastern Timor Sea(?T value is Big).When the summer sunshine in the southern hemisphere is low,the NW monsoon is weak,and the ITF of the surface water is weakly inhibited.At this time,the ITF activity of the surface water is strong,and the thermocline in the eastern Timor Sea is deep(the ΔT value is small).The spectral intensity of all proxies from core MD98-2172 is concentrated in 100 ka,41ka and 23 ka.Unlike the sedimentary records of adjacent core MD01-2318,which only show a clear tropical response(23ka and 19ka),all the sedimentary records of the MD98-2172 core in this paper also show a strong obliquity signal(41ka),indicating that monsoon and ITF activities in eastern Timor Sea are affected by obliquity-driven(41ka),in addition to precession-driven(23ka).