Variations in late Quaternary upper ocean structure of Okinawa Trough:A nannofossil approach  

作　　者：成鑫荣 汪品先 

出　　处：《Science China Earth Sciences》1998年第3期290-296,共7页中国科学（地球科学英文版）

基　　金：ProjectsupportedbytheNationalNaturalScienceFoundationofChina (GrantNos.4 9776 2 89and 4 94 0 6 0 6 7) .

摘　　要：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.The relative abundance of Florisphaera 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 of F. 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 of Pulleniatina obliquiloculata, a tropical planktonic foraminiferal 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.

关 键 词：UPPER ocean OKINAWA TROUGH CALCAREOUS NANNOFOSSIL nutricline thermocline. 

分 类 号：P722.6[天文地球—海洋科学]