Rare earth elements(REE) compositions and discriminant function were successfully used to examine high resolution sediment source changes in the northern Okinawa Trough over the last 24.1 ka,especially for the influence from the Yellow River and the Tsushima Warm Current(TWC) that has not been well solved.Variations of these parameters were clearly divided into three distinct depositional units.During Interval 1(24.1-16.0 ka BP),the paleo-Yellow River and the paleo-Yangtze River mouths were situated near the studied area and could have played major roles in the sedimentation therein.In Interval 2(16.0-7.3 ka BP),these river mouths gradually retreated with global sea-level rise,leading to less fluvial inputs from them to the northern Okinawa Trough.Meanwhile,formation of the TWC could carry some sediment loads of Taiwan to the studied core,especially during its late phase(8.0-7.3 ka BP).Modern oceanographic conditions,with a predominance of the TWC,were finally established since the beginning of Interval 3,causing more terrigenous contribution from Taiwan to the studied area.Sub-sequently,modern depositional environments mainly influenced by the Yellow River,the Yangtze River,and the TWC were finally formed.
Southern Hemisphere mid-latitude westerlies contribute to the ventilation of the deep Southern Ocean(SO),and drive changes in atmospheric carbon dioxide(CO2) and the global climate.As the westerlies control directly oceanic fronts,the movement of the subtropical front(STF) reflects the westerlies migration.Thus it is important to understand the relationships between STF movement and the weaterlies,ventilation of the deep SO,ice volume and atmospheric CO2.To this end,we use two new high-resolution records from early Marine Isotope Stage(MIS) 20(～800 ka) of sea surface temperature(SST) based on U k' 37 paleo-thermometer and benthic oxygen isotope(δ 18OB) at Ocean Drilling Program(ODP) Site 1170B in the southern Tasman Sea(STS),to construct linkages between the marine records and atmospheric proxies from Antarctic ice-cores.During the last 800 ka,the average SST(10.2℃) at Site 1170B is 1.8℃ lower than today(annual average 12℃).The highest average SST of 11.6℃ occurred during MIS 1,and the lowest average SST of 7.8℃ occurred during MIS 2.The warmest and coldest records of 14.7℃ and 6.2℃ occurred in the MIS 5 and MIS 2,respectively.In the glacial-interglacial cycles of the last 800 ka,variability of reconstructed SST shows that the STF moved northward or southward more than 3° of latitude compared with its present location.In the warmest stage MIS 5,the STF shifted to its southernmost location of ～49°S.In contrast,in the coldest stage MIS 2,the STF moved to its northernmost location of ～43°S.In response to orbital cycles,the westerlies movement led ice volume and atmospheric CO2 changes,but it was in phase with change in Antarctic atmospheric temperature.Ice volume only preceded atmospheric CO2 only a little at the 23-ka precession band,lagged the atmospheric CO2 at the 100-ka eccentricity band,and was in phase with atmospheric CO2 at the 40-ka obliquity band.
LI WenBaoWANG RuJianXIANG FeiDING XiaoHuiZHAO MeiXun
To investigate the relationship between volcanic activity and sediment record on regional and temporal scales,158 surface sediment samples were collected from the East China Sea Shelf to the northern Okinawa Trough (OT),and two cores recovered in the northern and southern OT,respectively.Mineralogy,grain-size,and geochemical analyses of those samples show that:1) volcanic glass,volcanic-type pyroxene,hypersthenes,and magnetite increase in sediment influenced by volcanic activity;2) sediment grain sizes (and also silt content) increase in ash layers;and 3) the contents of Na2O and Zr are higher,while terrigenous elements,e.g.,TFe2O3 and K2O,and biogenous compositions,e.g.,CaO and Sr,are relatively lower in ash layers than those of non-ash layers.The distribution of volcanic ash has three distinguishing characteristics:1) volcanic ash is more abundant in the northern and central OT than the southern OT;2) volcanic ash increases from continental shelf to the trough;3) the sediment during the last 12 000 a suggests stronger volcanic events than during 15 000-12 000 a.The eruptive locations,frequency,and volume of calderas are among the most important factors controlling the distributions of volcanic ash.In addition,the main Kuroshio warm current that extends northward probably impeded the diffusion of volcanic ash to the west and south in the OT.However,a southward current probably carried some volcanic ash toward southern OT.
