Variation And Driving Factors Of Sea Surface Temperature And Salinity In The Southwest Of The Timor Sea Over The Past 620 Ka

The Indonesia Throughflow(ITF),which regulates the water and heat exchange between the Pacific Ocean and Indian Ocean,has significant influence on the recent climate and environments in the Indo-Pacific region.Also,it exerted a crucial role in the evolution of regional hydrological conditions during the past times.However,most of the existing researches on the changes of ITF in geological history are limited to the last glacial period with insufficient knowledge on its evolution over multiple glacial cycles.International Ocean Discovery Program(IODP)Site U1482(Expedition 363)is within the main path of outflow of ITF at 15°3.32?S,120°26.10?E and 1466 m below sea level(mbsl).In this study,the upper 42.48 m core composite depth below seafloor(CCSF)of site U1482 was used to reconstruct the sea surface temperature(SST)based on?¹⁸O and Mg/Ca analyses of planktonic foraminifera Trilobatus sacculifer(T.sacculifer),and thus to investigate the variations in the seawater residual oxygen isotope(?¹⁸O_sw-iv)over the past 620 ka.Combined with other paleoclimate records from the Western Pacific Warm Pool(WPWP),ITF pathway and mid-high latitudes,the characteristics of temperature and salinity changes in the multiple glacial cycles were analyzed to reveal the possible factors that determine their changes.The SST record shows a clear character,with higher and lower values during the interglacial and the glacial,respectively.Spectral analysis of the SST reveals that spectral power concentrate in the precession(23 ka,19 ka)period,obliquity(41 ka)period and eccentricity(100 ka)period.The precession signal may come from the ITF source area and its transportation process.When Asian monsoon and precipitation caused by the Intertropical Convergence Zone(ITCZ)significantly affected the intensity and structure of the ITF.Also,the local factors,such as insolation and prevailing wind direction alternation have strengthened the precession signal of SST.The periodic variations in the intensity of the Agulhas current(AC),which controls the heat transfer from the Indian Ocean to the South Atlantic,and the warm poleward ocean southwards Leeuwin Current(LC)resulted in the obliquity signal of SST in the study area.The eccentricity cycle characteristics of the SST are mainly origin from the response of the region SST to periodic changes of global sea surface temperature during the glacial cycle.The variability of?¹⁸O_sw-iv,which has a positive correlation with sea surface salinity(SSS),shows significant precession(23 ka)and obliquity(40 ka)cycles,with higher values during the interglacial over the past 620 ka.Analysis shows that the?¹⁸O_sw-iv characteristics of the study area are less affected by local atmospheric precipitation and river input,but more affected by the factors,such as the changes of ITF structure and intensity and global sea level fluctuations.The periodic alternations of prevailing wind and the meridional migrations of the ITCZ driven by precession could influence the structure and strength of the ITF,and then the salinity in the southwest of the Timor Sea.The glacial cycles of the?¹⁸O_sw-iv record coincides with the periodic onset of deglaciation,indicating the considerable role of the global sea level fluctuations in the regional hydrology during the glacial cycle that determined the connectivity of the ITF channels among the Indonesian archipelagos.The variations in the meridional temperature gradient in the southern hemisphere driven by the obliquity of the earth's orbit could also affect the southward transport of the ITF fresh water to the high latitude areas and caused the?¹⁸O_sw-iv in the study area to exhibit obliquity period of 40 ka.This study also analyzes the practical problems encountered in the deployment of mooring systems equipped with sediment traps in the Westernest Pacific and gives a solution for the issue.For the issue of high sample loss rate(about 20%)due to sample bottle dropping,a reinforcement measure based on the local ocean current circumstances is presented for the deployment of sediment trap system in the open ocean with powerful hydrodynamic conditions.And,a special fixing cable-tie for the fastening of sediment sample bottles to protect sample bottles from losing was designed to achieve the purpose of safe recovery of samples.