The relative abundance ofFlorisphueru profunda, a calcareous nannofossil species in lower euphotic zone, affords an opportunity to study variations in upper ocean structure such as thickness of mixed layer. As reveale...The relative abundance ofFlorisphueru profunda, a calcareous nannofossil species in lower euphotic zone, affords an opportunity to study variations in upper ocean structure such as thickness of mixed layer. As revealed by the nannofossil analysis in sediments since 20 ka B. P. from three Okinawa Trough cores, the percentage ofF. profunda increased significantly from glacial to Holocene, with a declining event ca 4 ka B. P. in its southern part. Its downcore trend is similar to that ofPulleniatina obliquiloculuta, a tropical planktonic foraminifera1 species which lives in subsurface water below thermocline in the modern ocean. Their similar variations imply an eastward shift of the Kuroshio Current, a reduction in thickness of the mixed layer, a shallowing of thermocline and a possible increase of turbidity in the upper ocean during the glaciation. The eastward shift of the Kuroshio might be repeated again about 4 ka B.P.展开更多
Okinawa Trough is a back-arc, initial marginal sea basin, located behind the Ryukyu Arc-Trench System. The formation and evolution of the Okinawa Trough is intimately related to the subduction process of the Philippin...Okinawa Trough is a back-arc, initial marginal sea basin, located behind the Ryukyu Arc-Trench System. The formation and evolution of the Okinawa Trough is intimately related to the subduction process of the Philippine Sea Plate beneath the Eurasian Plate since the late Miocene. The tectonic evolution of the trough is similar to other active back-arcs, such as the Mariana Trough and southern Lau Basin, all of which are experiencing the initial rifting and subsequent spreading process. This study reviews all petrologic and geochemical data of mafic volcanic lavas from the Okinawa Trough, Ryukyu Arc, and Philippine Sea Plate, combined with geophysical data to indicate the relationship between the subduction sources （input） and arc or back-arc magmas （output） in the Philippine Sea Plate-Ryukyu Arc-Okinawa Trough system （PROS）. The results obtained showed that several components were variably involved in the petrogenesis of the Oki-nawa Trough lavas：sub-continental lithospheric mantle underlying the Eurasian Plate, Indian mid-oceanic ridge basalt （MORB）-type mantle, and Pacific MORB-type mantle. The addition of shallow aqueous fluids and deep hydrous melts from subducted components with the characteristics of Indian MORB-type mantle into the mantle source of lavas variably modifies the primitive mantle wedge beneath the Ryukyu and sub-continental lithospheric mantle （SCLM） beneath the Okinawa Trough. In the northeastern end of the trough and arc, instead of Indian MORB-type mantle, Pacific MORB-type mantle dominates the magma source. Along the strike of the Ryukyu Arc and Okinawa Trough, the systematic variations in trace element ratios and isotopic compositions reflect the first-order effect of variable subduction input on the magma source. In general, petrologic data, combined with geophysical data, imply that the Okinawa Trough is experiencing the＂seafloor spreading＂process in the southwest segment,＂rift propagation＂process in the middle seg-ment, and＂crustal extension＂process in 展开更多
利用NCEP再分析的大气环流资料、海表温度资料和全国160站降水资料,研究了冬季东印度洋海温对我国江南-华南地区同期降水的影响。结果指出,冬季东印度洋海温(Sea Surface Temperature in theEastern Indian Ocean,EIOSST)和同期的江南-...利用NCEP再分析的大气环流资料、海表温度资料和全国160站降水资料,研究了冬季东印度洋海温对我国江南-华南地区同期降水的影响。结果指出,冬季东印度洋海温(Sea Surface Temperature in theEastern Indian Ocean,EIOSST)和同期的江南-华南降水呈显著的正相关关系。当EIOSST偏高时,江南-华南的冬季降水偏多。而当EIOSST偏低时,江南-华南的冬季降水偏少。这种影响的可能机制是:冬季东印度洋海温异常通过影响南支槽上的扰动活动和水汽输送来影响同期的江南-华南降水。当东印度洋海温偏高时,局地对流加强,引起南支槽地区的上升运动加强,南支槽活跃。活跃的南支扰动向下游传播,南支槽前的西南气流将水汽从孟加拉湾向华南和江南输送,引起华南和江南的降水偏多。进一步的分析显示,东印度洋海温对南支槽和江南-华南的降水的影响独立于ENSO的影响。二者对南支槽和江南-华南地区冬季降水的影响过程一致,只是东印度洋海温的影响较弱。当东印度洋海温和ENSO的作用相叠加时,江南-华南可能会出现较异常的冬季降水。展开更多
文摘The relative abundance ofFlorisphueru profunda, a calcareous nannofossil species in lower euphotic zone, affords an opportunity to study variations in upper ocean structure such as thickness of mixed layer. As revealed by the nannofossil analysis in sediments since 20 ka B. P. from three Okinawa Trough cores, the percentage ofF. profunda increased significantly from glacial to Holocene, with a declining event ca 4 ka B. P. in its southern part. Its downcore trend is similar to that ofPulleniatina obliquiloculuta, a tropical planktonic foraminifera1 species which lives in subsurface water below thermocline in the modern ocean. Their similar variations imply an eastward shift of the Kuroshio Current, a reduction in thickness of the mixed layer, a shallowing of thermocline and a possible increase of turbidity in the upper ocean during the glaciation. The eastward shift of the Kuroshio might be repeated again about 4 ka B.P.
基金The National Natural Science Foundation of China under contract Nos 41322036,41230960,40906034,41276003 and 41176058China Ocean Mineral Resources R&D Association(COMRA)under contract No.DY125-12-R-05
文摘Okinawa Trough is a back-arc, initial marginal sea basin, located behind the Ryukyu Arc-Trench System. The formation and evolution of the Okinawa Trough is intimately related to the subduction process of the Philippine Sea Plate beneath the Eurasian Plate since the late Miocene. The tectonic evolution of the trough is similar to other active back-arcs, such as the Mariana Trough and southern Lau Basin, all of which are experiencing the initial rifting and subsequent spreading process. This study reviews all petrologic and geochemical data of mafic volcanic lavas from the Okinawa Trough, Ryukyu Arc, and Philippine Sea Plate, combined with geophysical data to indicate the relationship between the subduction sources （input） and arc or back-arc magmas （output） in the Philippine Sea Plate-Ryukyu Arc-Okinawa Trough system （PROS）. The results obtained showed that several components were variably involved in the petrogenesis of the Oki-nawa Trough lavas：sub-continental lithospheric mantle underlying the Eurasian Plate, Indian mid-oceanic ridge basalt （MORB）-type mantle, and Pacific MORB-type mantle. The addition of shallow aqueous fluids and deep hydrous melts from subducted components with the characteristics of Indian MORB-type mantle into the mantle source of lavas variably modifies the primitive mantle wedge beneath the Ryukyu and sub-continental lithospheric mantle （SCLM） beneath the Okinawa Trough. In the northeastern end of the trough and arc, instead of Indian MORB-type mantle, Pacific MORB-type mantle dominates the magma source. Along the strike of the Ryukyu Arc and Okinawa Trough, the systematic variations in trace element ratios and isotopic compositions reflect the first-order effect of variable subduction input on the magma source. In general, petrologic data, combined with geophysical data, imply that the Okinawa Trough is experiencing the＂seafloor spreading＂process in the southwest segment,＂rift propagation＂process in the middle seg-ment, and＂crustal extension＂process in
文摘利用NCEP再分析的大气环流资料、海表温度资料和全国160站降水资料,研究了冬季东印度洋海温对我国江南-华南地区同期降水的影响。结果指出,冬季东印度洋海温(Sea Surface Temperature in theEastern Indian Ocean,EIOSST)和同期的江南-华南降水呈显著的正相关关系。当EIOSST偏高时,江南-华南的冬季降水偏多。而当EIOSST偏低时,江南-华南的冬季降水偏少。这种影响的可能机制是:冬季东印度洋海温异常通过影响南支槽上的扰动活动和水汽输送来影响同期的江南-华南降水。当东印度洋海温偏高时,局地对流加强,引起南支槽地区的上升运动加强,南支槽活跃。活跃的南支扰动向下游传播,南支槽前的西南气流将水汽从孟加拉湾向华南和江南输送,引起华南和江南的降水偏多。进一步的分析显示,东印度洋海温对南支槽和江南-华南的降水的影响独立于ENSO的影响。二者对南支槽和江南-华南地区冬季降水的影响过程一致,只是东印度洋海温的影响较弱。当东印度洋海温和ENSO的作用相叠加时,江南-华南可能会出现较异常的冬季降水。
