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The relative abundance ofFlorisphueru profunda, a calcareous nannofossil species in lower euphotic zone, affords an opportunity to study variations in upper ocean structure
such as thickness of mixed layer. As revealed by the nannofossil analysis in sediments since 20 ka B. P. from three Okinawa
Trough cores, the percentage ofF. profunda increased significantly from glacial to Holocene, with a declining event ca 4 ka B. P. in its southern part. Its downcore
trend is similar to that ofPulleniatina obliquiloculuta, a tropical planktonic foraminifera1 species which lives in subsurface water below thermocline in the modern ocean. Their
similar variations imply an eastward shift of the Kuroshio Current, a reduction in thickness of the mixed layer, a shallowing
of thermocline and a possible increase of turbidity in the upper ocean during the glaciation. The eastward shift of the Kuroshio
might be repeated again about 4 ka B.P.
Project supported by the National Natural Science Foundation of China (Grant Nos. 49776289 and 49406067) 相似文献
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A great number of calcareous nannofossils have been found in the deep-sea sediments of 2.32 Ma at ODP Site 1143 located in
the Nansha area, the southern South China Sea. The number of coccoliths varies from about 0.5×106 up to almost 53×106 coccoliths/g sediment, with an average of 16×106 coccoliths/g sediment. The accumulation rate of total coccoliths varies from 1×106 to 278×106 coccoliths/cm2 ka. The nannofossil assemblages are usually dominated by a lower-photic species-Florisphaera profunda, of which the average percentage is about 70% in all samples. The absolute abundance and the accumulation rate of nannofossils
as well as the percentage ofF. profunda display significant oscillations on two different time scales. One is the fluctuation coincident with the glacial-interglacial
cycle, and the other is the long-term changes on a time scale longer than 100 ka. Six evolutionary stages of calcareous nannofossils
could be divided for the last 2.32 Ma, from which we can reconstruct the changes in the depth of nutricline of the Nansha
area. In this paper, the possible mechanism resulting in these variations is also discussed. 相似文献
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Zhimin Jian 《中国科学D辑(英文版)》1998,41(4):337-344
Based on the oxygen and carbon stable isotopic records of benthic foraminifera in nine deep-sea cores of the South China Sea
(SCS), the bathymetric profiles of δ18O and δ13C since the last glacial maximum (LGM) are preliminarily established. The bathymetric gradients of deep-water δ18O and δ13C in the SCS are obviously greater during the LGM than during the Holocene, showing the existence of the deep thermocline
and nutricline at water depth of about 2 000 m. Particularly, the differences in δ18O and δ13C between the LGM and Holocene, from which the ice-volume effect and the global mean shift have been subtracted respectively,
are positive values at water depths of 1 000–2 500 m in the SCS. This indicates the existence of deep-water mass with relatively
cool temperature or higher salinity, better ventilation and more δ13C within the water depth range of the SCS during the LGM, which is distinctly different from that at present. These changes
further confirm the existence of the glacial “North Pacific Deep Water” which, however, is possibly confined to the water
depth range of 1 000–2 500 m.
Project supported by the National Natural Science Foundation of China (Grant Nos. 49576286 and 49732060). 相似文献
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末次冰消期以来苏拉威西海颗石藻化石记录与古海洋变化 总被引：1，自引：0，他引：1
通过对苏拉威西海MD98-2178柱状样(3.62°N、118.70°E)颗石藻化石属种相对含量的统计,重建了2万年来海水古生产力、营养跃层的变化。其中Emiliania huxleyi、Gephyrocapsa oceanica、Florisphaera profunda占颗石藻群落的80%～90%。由于G.oceanica与F.profunda存在于两种完全不同的生态环境中,两者的变化趋势完全相反。前者代表高生产力以及高营养物质的海水,后者则代表低生产力与较深的营养跃层。推测冰消期颗石藻对环境变化具有两种响应模式:以约13.5ka的生产力峰值期为界,13.5ka之前颗石藻古生产力变化主要响应于径流对海洋营养物质的输入,而13.5ka之后则主要响应于海水-大气之间水循环的强度。全新世F.produnda含量及其所反映的营养跃层变化具有明显的百年尺度波动,与太阳活动的100～260a周期具有良好的相关性。推测全新世苏拉威西海区营养跃层变化受百年尺度的类似厄尔尼诺-南方涛动(El Nino-Southern Osillation,ENSO)的变化及太阳活动的驱动。 相似文献
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