末次冰期以来中国海区浮游有孔虫Pulleniatina obliquiloculata含量变化的地层学意义

西北太平洋尤其是中国海区末次冰期旋回中浮游有孔虫Pulleniatina obliquiloculata含量变化研究是近年来最重要的古海洋学内容之一.作者综合分析了中国及邻近海区具有可靠测年地层的深海沉积物柱状样中P.obliquiloculata含量变化,探讨其含量低值事件(PME)的生物地层学意义.末次冰期以来P.obliquiloculata含量变化在中国海区呈现两种变化模式:一是以东海及南海北部为代表的冰期含量低、间冰期含量高的特点;另一种则是南海南部的冰期含量高、间冰期含量低的现象.高分辨率地层记录显示,在这种冰期/间冰期总体变化趋势基础上,我国东海、南海和黑潮源区等广泛存在晚全新世～4 300-2 800 cal yr BP P.obliquiloculata含量低值,但以南海北部与东海冲绳海槽最为明显;而南海南部P.obliquiloculata含量还在冰消期(～16.5-15 cal kyr BP)有另一特征的低含量阶段.因而,末次冰期旋回中国海区P.obliquiloculata含量变化可以作为区域性地层划分和对比的标志.尽管如此,由于黑潮分支水团的影响,冲绳海槽中部和北部部分海域,在末次冰期与PME期间,P.obliquiloculata虽然含量相对较低,但仍可保持3%-5%以上,而非多数站位PME事件中的特征性零含量.研究表明PME事件主要由次表层海水的温度降低、温跃层变浅、上部水体温度梯度增加等引起,与表层海水无关,但引起这些海洋环境变化的原因尚不清楚.

VARIATIONS OF PULLENIATINA OBLIQUILOCULATA ABUNDANCE IN THE CHINA SEA SINCE THE LAST GLACIAL PERIOD AND THEIR STRATIGRAPHIC SIGNIFICANCE

Pulleniatina obliquiloculata is one of the most important planktonic foraminiferal species in the West Paci-fic over the last glacial-interglacial periods. In this study, variations of P. obliquiloculata abundance in the China Sea and the adjacent region are reviewed to evaluate their significance in stratigraphy. There are two patterns for the vari-ations of P. obliquiloculata in the China Sea. One is the lower glacial- and higher interglacial- contents in the Okina-wa Trough (OT) and the northern South China Sea (SCS) ; and the other is the higher glacial- and lower interglacial-contents in the Southern SCS. High-resolution records indicate that a late Holocene P. obliquiloculata minimum (PME) distributed in all the China Sea, while the southern SCS has another characteristic PME during the beginning of the last deglaciation. P. obliquiloculata abundance was even lowered to zero in the China Sea during these PME events. The late Holocene PME occurred at～4 300-2 800 cal yr BP, while the last deglacial PME was a t～16.5-15 cal kyr BP, correlated to the Heinrich event 1. Therefore, the variations of P. obliquiloculata abundance and the evident PME events can be adopted as stratigraphic tools in the China Sea over the last glacial-interglacial periods. P. obliquiloculata minimum contents were found to be more than 3%-5% during the late Holocene PME in several sites of the middle and northern OT, which suggested some influence of the Kuroshio branch during that period. The PME events were often accompanied with the cooling of the subsurface water or the shoaling of the thermocline, in-stead of the changes in the sea surface property. However, the cause of the sea subsurface change is still unclear.