冲绳海槽南部两万年来碳酸盐溶跃面的变迁

VARIATIONS IN THE LYSOCLINE OF CARBONATE IN THE SOUTHERN OKINAWA TROUGH DURING THE LAST 20 000 YEARS

对冲绳海槽南部表层沉积和晚第四纪沉积柱状样中百余个样品进行了浮游及底栖有孔虫、翼足类等微体化石定量分析。通过表层沉积样品中底栖有孔虫占有孔虫全群比例、底栖有孔虫群中胶结质壳比例、浮游有孔虫碎壳率和浮游及底栖有孔虫丰度等多种标志的水深变化，确定冲绳海槽现代的碳酸盐溶跃面位于水深１５００～１６００ｍ处。进而，在高分辨率地层学基础上，检验这些指示溶解作用的标志和翼足类丰度等在柱状样中的变化，结果发现末次冰期冲绳海槽碳酸盐溶解作用显著减弱，碳酸盐溶跃面和文石补偿深度急剧变深；至冰后期碳酸盐溶解作用又急剧增强，溶跃面和文石补偿深度又变浅至与现代相当的位置。这些变化与南海等西太平洋其他海区的特征相一致。

Quantitative analysis of microfossils(planktonic and benthic foraminifera,and pteropod)has been carried out for more than one hundred samples in the surface sediments and late Quaternary sedimentary core of the southern Okinawa Trough.Based on the bathymetric variations in the ratio of benthic foraminifera to total foraminiferal fauna,ratio of agglutinants to benthic foraminiferal fauna,ratio of planktonic foraminiferal fragmentation and abundances of planktonic and benthic foraminifera,the modern carbonate lysocline in the Okinawa Trough is determined to be located at the depths of 1 500～1 600m.Furthermore,on the basis of high resolution stratigraphy,the variations in these indicators of carbonate dissolution and also abundance of pteropod are examined.In result,it was found that during the last glacial stage the carbonate dissolution greatly decreased,and the carbonate lysocline and Aragonite Compensation Depth (ACD) deepened in the Okinawa Trough,while during the post glacial stage the carbonate dissolution remarkably increased and the carbonate lysocline and ACD became shallow to their modern depths.These changes are consistent to those in the South China Sea and other sea areas of the West Pacific.