在古海洋学研究中,常用浮游有孔虫来恢复表层海水温度(SST),然而基于浮游有孔虫恢复SST的这些方法之间存在一定的差异。为了说明各方法的特点,在浮游有孔虫鉴定和浮游有孔虫表层种Globigerinoides ruberMg/Ca比值测试的基础上,分别利用转换函数FP12-E,现代类比(Modern Analog Technique,MAT)和Mg/Ca比值法对西北太平洋北赤道流分叉处MD06-3054孔中记录的末次冰期以来的SST进行了估算。分析发现:(1)转换函数FP12-E不适用于该孔;(2)该孔中MAT法估算的末次冰期到冰后期SST的变化小于Mg/Ca比值法得到的结果;(3)考虑到浮游有孔虫产量的季节变化,Mg/Ca比值法得到的SSTMg/Ca末次冰期到冰后期的变化可能偏大。尽管如此,相对于MAT等古生态学方法,Mg/Ca比值法受到的影响因素更少,若能对浮游有孔虫的季节产量等方面加以校正,将会得到更准确的结果。
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.
In the warming world,tropical Pacifi c sea surface temperature(SST)variation has received considerable attention because of its enormous infl uence on global climate change,particularly the El Ni?o-Southern Oscillation process.Here,we provide new high-resolution proxy records of the magnesium/calcium ratio and the oxygen isotope in foraminifera from a core on the Ontong-Java Plateau to reconstruct the SST and hydrological variation in the center of the Western Pacifi c Warm Pool(WPWP)over the last360000 years.In comparison with other Mg/Ca-derived SST and δ^(18)O records,the results suggested that in a relatively stable condition,e.g.,the last glacial maximum(LGM)and other glacial periods,the tropical Pacifi c would adopt a La Ni?a-like state,and the Walker and Hadley cycles would be synchronously enhanced.Conversely,El Ni?o-like conditions could have occurred in the tropical Pacifi c during fastchanging periods,e.g.,the termination and rapidly cooling stages of interglacial periods.In the light of the sensitivity of the Eastern Pacifi c Cold Tongue(EPCT)and the inertia of the WPWP,we hypothesize an inter-restricted relationship between the WPWP and EPCT,which could control the zonal gradient variation of SST and aff ect climate change.
Changes in sea surface temperature(SST), seawater oxygen isotope(δ 18 O sw), and local salinity proxy(δ 18 O sw-ss) in the past 155 ka were studied using a sediment core(MD06-3052) from the northern edge of the western Pacifi c Warm Pool(WPWP), within the fl ow path of the bifurcation of the North Equatorial Current. Our records reveal a lead-lag relationship between paired Mg/Ca-SST and δ 18 O during Termination II and the last interglacial period. Similarity in SST between our site and the Antarctic temperature proxy and in CO 2 profi le showed a close connection between the WPWP and the Antarctic. Values of δ 18 O sw exhibited very similar variations to those of mean ocean δ 18 O sw, owing to the past sea-level changes on glacial-interglacial timescale. Calculated values of δ 18 O sw-ss refl ect a more saline condition during high local summer insolation(SI) periods. Such correspondence between δ 18 O sw-ss and local SI in the WPWP may refl ect complex interaction between ENSO and monsoon, which was stimulated by changes in solar irradiance and their infl uence on the local hydrologic cycle. This then caused a striking reorganization of atmospheric circulation over the WPWP.
The deglacial δ~13C minimum events that originated from the ventilation of the deep Southern Ocean around Antarctica, have been recorded in a range of marine sediments from the southern to tropical oceans in late Pleistocene. However, the broad δ~13C minimum event was also reported as far as to the northern middle latitudes, in northwestern Pacific marginal sea areas, during the last deglaciation. In the northwestern Pacific, forcing from the northern high latitudes is strongly expressed, while the records of in- fluence from the southern high latitudes are few. The Kuroshio Source Region (KSR) forms a boundary between the northwestern Pacific and the southern, tropical Pacific. So, high-resolution planktonic foraminiferal records in core MD06-3054 from the KSR are well positioned to identify signals from the southern hemisphere in the northwestern Pacific. Planktonic foraminiferal tests from the upper 1030 cm of the core were subject to AMS14C, carbon and oxygen isotopic measurements. A negative excursion was found to occur from about 20.0-6.0 ka BP in δ~13C records of both surface (Globigerinoides ruber) and subsurface (Pulleni- atina obliquiloculata) dwellers, but the overall trends of the two curves have reversed since 26.5 ka BP. Moreover, the δ~13C rec- ord of G. ruber (the surface dweller) shows a robust link to the record of atmospheric CO2, and its changes precede the records of P. obliquiloculata (the subsurface dweller). According to the hydrologic conditions, the broad δ~13C minimum event recorded in the KSR is also a response to the increasing ventilation of the deep Southern Ocean around Antarctica during the last deglaciation. The inconsistency between the records of the surface and subsurface dwellers was possibly caused by the ways that the low δ~13C signal was transmitted. Subsurface water primarily received the low δ~13C signal from the Antarctic Intermediate Water (AAIW), whereas the surface water was probably mainly impacted by atmospheric CO2 in the KSR. The records from the KSR confi
