冲绳海槽北部陆坡4.4万年以来古海洋环境演化的地质记录

PALEOENVIRONMENTAL CHANGES ON THE CONTINENTAL SLOPE OF THE NORTHERN OKINAWA TROUGH DURING THE PAST 44 000 YEARS

利用AMS 14C年代测试、氧同位素分析和浮游有孔虫分析重建了冲绳海槽北部陆坡 DOC 42 孔约 44cal.kaBP以来的古海洋环境演化记录。DOC 42孔沉积速率整体较低, 呈明显的阶段性变化: 在氧同位素 3 期和LGM期间沉积速率相对较大,分别为7 3和14 cm/ka; 末次冰消期以来的沉积速率则显著降低, 与冲绳海槽冰后期沉积速率高于末次冰期明显不同; 自约6 4 cal.kaBP以来, 沉积物堆积作用基本可以忽略, 表明了受黑潮入侵引起的中国东部陆架环流体系的改变, 岩心所在区域的沉积格局发生了重大变化。浮游有孔虫氧碳同位素、转换函数古温度和低温、低盐特征种Globigerina quinqueloba 等一致反映了冲绳海槽北部在氧同位素 3 期早期约 37 5~44 cal.kaBP期间存在明显的低温、低盐阶段, 表明该期间冲绳海槽北部的沿岸冲淡水影响明显加强,而在氧同位素3期晚期该区可能受到了黑潮暖流的影响。此外, 浮游有孔虫 Pulleniatina obliquiloculata 与氧同位素记录有很好的对应关系, 表明它是冲绳海槽末次冰期以来的一个可靠的海洋环境指标。

Planktonic foraminifera, oxygen and carbon isotopes have been studied in core DOC-42 from the continental slope of the northern Okinawa Trough to reconstruct the paleoenvironmental evolution history of the surface water. AMS ^(14)C dating on six horizons revealed that core DOC-42 preserved a geological record of 44 000 cal.aBP. Sedimentation rate (SR) is very low on the whole core and shows three apparent variations at three phases: ①A comparatively high SR during marine isotope stage 3 (MIS3) and LGM, about 7.3 and 14 cm/ka respectively;②A very low SR of 1.5 cm/ka during the last deglaciation, which is different from the deeper Okinawa Trough with higher SR during the last deglaciation than the last glaciation; ③A negligible sediment accumulation since 6.4 cal.kaBP, which may correspond to the changed current pattern of the East China shelf seas aroused by the intrusion of the warm Kuroshio Current in the early Holocene. A stage with apparent low temperature and low salinity during early MIS3 at about 37.5~44 cal.kaBP was conformably indicated by oxygen and carbon isotope records of N. dutertrei,and temperatures estimated from Transfer Functions and planktonic foraminiferal species ofG. quinqueloba, suggest that the northern Okinawa Trough received enhanced influence of fresh water discharge from the Chinese continent during this period. During late MIS3 the northern Okinawa Trough may be affected by the warm Kuroshio Current intrusion. In addition, planktonic foraminiferal species of P. obliquiloculatashows a good relation with the oxygen isotope record and acts as a paleoceanographic indicator even during the last glacial in the Okinawa Trough.