冲绳海槽西南部二万年来的深海介形虫和古环境变化

从冲绳海槽西南部255柱状样采集114个沉积物样品进行介形虫定量分析，结合有孔虫、同位素和碳酸钙含量等资料探讨东海二万年来的古环境变化历史。依据属种组成、数量、丰度及分异度，在255柱状样中识别出与全球气候变化相应的冰期、冰消期和冰后期三个介形虫组合。冰期组合以优势种Palmoconcha parapontica和Loxoconchidea aff.dolgoiensis为特征，数量丰度和分异度高，但缺乏大洋性类型，推测冰期低海面时期底层水体呈富养低氧和较封闭的状态。冰消期和冰后期以Krithe spp.和Legitimocythere acanthode4rma占优势，丰度显著减少，出现较多的大洋性类型，推测冰消期以来海面上升和岸线后退及黑潮加强致使生产力下降，深海为低营养和高流通状态。

DEEP-SEA OSTRACODS AND PALEOENVIRONMENTAL CHANGES OF THE SOUTHWESTERN OKINAWA TROUGH DURING THE LAST 20 KA

Ostracods from 114 sediment samples of core 255 (water depth 1 575 m, core length 6.55 m, southwestern Okinawa Trough) were quantitatively studied for interpreting the paleoenviromental changes of the East China Sea during the last 20 ka, in combination with the data of stable isotopes, CaCO_(3) content and foraminiferal fauna. Tree Ostracod assemblages are identified, associated with glacial, deglacial and postglacial stages, respectively. The glacial assemblage is marked by the dominant species Palmoconcha parapontica and Loxoconchidea aff. dolgoiensis, high abundance and species diversity, and lack of cosmopolitan oceanic species, probably indicating the high-nutrient and low-oxygen bottom water which was less ventilation with the Pacific. Both deglacial and postglacial assemblages are predominated by Krithe spp. and Legitimocythere acanthoderma, in which abundance of P. parapontica and L. aff. dolgoiensis decreased while that of cosmopolitan oceanic species (L. acanthoderma and Henryhowella asperrima) increase remarkably. The abundance decreased especially in the postglacial period. It is suggested that the nutrient level in deep-sea decreased gradually with the increasing deepwater ventilation of the Okinawa Trough with the Pacific during the deglacial and postglacial periods. These changes are thought to be associated with the sea-level rise and concomitant retreat of the shoreline, and the enhancement of the Kuroshio Current since the deglaciation.