异地性介形虫堆积速率与古气候变化的相关性——以南海17940-2柱状样为例

ACCUMULATION RATES OF ALLOCHTHONOUS OSTRACODA AND CLIMATIC CHANGE, A CASE STUDY OF CORE 17940-2 FROM THE SOUTH CHINA SEA

17940 - 2柱状样采自南海北部陆坡、东沙群岛东南水深 172 7m处 ,柱长 1330 cm。通过分析该柱 4万年以来的介形虫化石群落 ,发现异地性浅水分子的堆积速率在末次冰期和气候转变期时明显呈现高值 ,而在相邻的两个转变期之间则偏低 ,尤其在冰后期气候较为平稳的整个全新世 ,异地性分子的堆积速率降到最低。这一变化与该孔中有机碳通量的变化趋势相一致 ,但与原地性介形虫堆积速率的变化截然不同。以上结果说明在古气候变化时期该海域陆坡表层沉积物的顺坡搬运作用明显增强 ,推测是因海平面变动激发所在站位上方浊流所至。本研究结果说明 。

Ostracods in a gravity core 17940 2 from the northern slope of the South China Sea (20°07′N, 117°23′E,water depth 1 727 m,length 1 315 cm)were analyzed to testify their usefulness in indicating paleoceanographic events. The oxygen isotopic stratigraphy and AMS 14 C datings show the core extends back about 40 000 aBP and documents the highest hemipelagic sedimentation rates ever found in SCS (19～85 cm/ka). A total of 95 samples were taken in 5～20 cm intervals for the quantitative analysis of Ostracoda. Total 94 species and/or genera were discriminated. Among them 47 taxa were divided into four groups according to their bathymetrical ranges. Group A is composed of 29 intertidal to inner shelf taxa; Group B, 7 middle and outer shelf taxa; Group C, 4 upper slope taxa; and Group D, 7 middle and lower slope taxa. Accordingly, taxa of Groups A～C in the core, which is sited at the middle slope, are allochthonous in nature. The downcore variations of accumulation rates (AR) of the above four ostracod groups were compared with the oxygen isotopic and organic carbon flux curves. The ARs of allochthonous ostracods (Groups A～C) show a covariance with the oxygen isotopic and organic carbon flux curves, being high during glacial time and low during the Holocene. The highest peaks always occurred in the climatic transitional phases. Such phenomenon indicates the changes in turbidity currents, which are more likely to be enhanced during rapid transgressions and regressions that are related to the rapid transitions between climatic events. The covariance in the ARs of allochthonous ostracods and organic carbon flux probably suggests that the organic carbon flux in core 17940 2 might also be affected by the turbidity currents.