首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 0 毫秒
1.
  总被引:13,自引:3,他引:10  
A 5-Ma record from ODP Site 1143 has re-vealed the long-term cycles of 400—500 ka in the carbon isotope variations. The periodicity is correlatable all over the global ocean and hence indicative of low-frequency changes in the ocean carbon reservoir. As the same periodicity is also found in carbonate and eolian dust records in the tropical ocean, it may have been caused by such low-latitude proc-esses like monsoon. According to the Quaternary records from Site 1143 and elsewhere, major ice-sheet expansion and major transition in glacial cyclicity (such as the Mid-Brunhes Event and the Mid-Pleistocene Revolution ) were all pre-ceded by reorganization in the ocean carbon reservoir ex-pressed as an episode of carbon isotope maximum (d 13Cmax), implying the role of carbon cycling in modulating the glacial periodicity. The Quaternary glacial cycles, therefore, should no more be ascribed to the physical response to insolation changes at the Northern Hemisphere high latitudes alone; rather, they have been driven by the 揹ouble forcing? a combination of processes at both high and low latitudes, and of processes in both physical (ice-sheet) and biogeochemical (carbon cycling) realms. As the Earth is now passing through a new carbon isotope maximum, it is of vital impor-tance to understand the cyclic variations in the ocean carbon reservoir and its climate impact. The Pre-Quaternary varia-tions in carbon and oxygen isotopes are characterized by their co-variations at the 400-ka eccentricity band, but the response of d 13C and d 18O to orbital forcing in the Quater-nary became diverged with the growth of the Arctic ice-sheet. The present paper is the second summary report of ODP Leg 184 to the South China Sea.  相似文献   

2.
As the third summary report of ODP Leg 184 to the South China Sea (SCS), this paper discusses the evolution of the East Asian monsoon and the SCS basin. A multi-proxy approach, involving geochemistry, micropale-ontology, pollen and other analyses, was adopted for reconstructing the evolutionary history of the East Asian monsoon, which was characterized by a series of paleo-climate events especially at 8, 3.2, 2.2 and 0.4 Ma. The new record indicates similar stages in the development of the East and South Asian monsoons, with an enhanced winter monsoon over East Asia being the major difference. The rich spectrums of monsoon variability from the southern SCS also reveal other characteristic features of the low latitude ocean. Evidence for the evolution of the SCS includes the hemipelagic Oligocene sediments, implying the existence of deep water environments during the early seafloor spreading stage of the SCS basin. The four major unconformities and some remarkabl ediagenetic features in upper Oligocene deposits indicate the strongest tectonic events in the region. From a careful comparison of lithologies and sedimentation rates, we conclude that the prominent differences in sedimentary environments between the southern and northern SCS were established only by ~3 Ma.  相似文献   

3.
Shallow marine sequences of the northern South China Sea (SCS) are uplifted and exposed by plate convergence in the Taiwan mountain belt. These deposits provide detailed geological information about the rifting event, stratigraphy, sedimentology, paleoclimate and paleoceanography of the shallow SCS to compare with what are recorded in the ODP 1148 deep-sea core. Seismic surveys and marine micropalentological studies show that Eocene sequences in the offshore Taiwan Strait and onland Taiwan mountain belt are all deposited in rifting basins and are covered unconformably by the Late Oligocene-Neogene post-rifting strata. Between syn-rifting and post-rifting sequences, there is a regional break-up unconformity throughout the island. Early Oligocene and Late Eocene strata are missing along the break-up unconformity equivalent to the T7 unconformity in the Pearl River Mouth Basin off south China. This may suggest that the SCS oceanic crust could have initiated between 33 and 39 Ma. Neither obvious stratigraphic gap nor slumping features are found in the Oligocene-Miocene transition interval of Taiwan. This observation highly contrasts with what has been documented from the ODP 1148 deep-sea core. This suggests that the stratigraphic gap and slumping features could only be recorded in the SCS deep sea region, but not in the shallow shelf near Taiwan. Compared to the Middle Miocene paleoceanographic re-organization events in the SCS deep sea, the geological history of the Taiwan shallow sequence shows changes of in sedimentation and faunal composition. Due to the Antarctic glacial expansion at~14 Ma, Middle to late Miocene strata of the Western Foothills show progressive regression sedimentations associated with a decrease of benthic foraminif-eral abundance and a sharp faunal turnover event. Many Early-Middle Miocene endemic benthic foraminifers were extinct in 14-13 Ma and new benthic foraminifers of the Kuroshio Current fauna appeared from 10.2 Ma, comparable with new occurrence of Modern benthic foraminifers at 9 Ma in the Java Sea area. This reveals that the Western Boundary Kuroshio Current in the North Pacific could initiate from 10-9 Ma due to closures of the Indo-Pacific seaways by convergent tectonics between the Australian Continent and the Indonesian Arc in 12-8 Ma. Subduction of the SCS oceanic lithosphere since the Middle Miocene resulted in formation of the Hengchun Ridge accretionary prism and the North Luzon Arc. Occurrence of these two bathymetric highs ( 2400 m) since the Middle Miocene and closures of the inter-arc passages in the North Luzon arc in the last 3.5 Ma would control the water exchanges between the West Pacific and the deep SCS. Accordingly, the tectonic evolution in the Central Range-Hengchun Peninsula accretionary prism and the arc-forearc Coastal Range not only control directly the route for water exchanges between the West Pacific and the SCS, but also indirectly shows a great influence on the geochemistry of deep SCS waters. The latter is best shown by much negative carbon isotope values of benthic foraminifers in the ODP 1148 deep-sea core than the West Pacific records in the last 14 Ma.  相似文献   

4.
  总被引:1,自引:0,他引:1  
Leg 184 of ODP recovered a record of deepwater sediments spanning the past 32.8 Ma from the South China Sea (SCS). The sediments of the Ofigocene (32.8-23.8 Ma) at Site 1148 contain relatively abundant fossil pollen. The pollen analysis at Site 1148 has established the first pollen assemblage sequence of deep-water Oligocene in the China Sea. The pollen assemblages of the Ofigocene are dominated by montane conifer tree pollen. The abundances of broad-leaved tree pollen are lower in the assemblages.Both of the montane conifer and broad-leaved tree pollen groups include mainly tropical-subtropical components. The pollen of cold and drought-enduring plants is present in lower content. The distinct change in pollen assemblage sequence of deep-water Oligocene of the SCS occurred at 32.0 Ma, indicative of an important shift of the Oligocene climate in the SCS region. The characteristics of the pollen flora of the deep-water Oligocene indicate the tropical montane ralnforest and lowland ralnforest developed on the areas around the SCS before 32.0 Ma, reflecting the warm and wet climatic condition. In the pollen flora of the Oligocene after 32.0 Ma, the temperate montane conifer and cool and drought-en- during deciduous tree taxa remarkably increased, indicating that the climate in the SCS region became comparatively cool and dry.  相似文献   

5.
Based on deep-sea pollen results (512-76 m) from ODP Site 1143 in the southern South China Sea (SCS),the climate and vegetation evolution sequence on the surrounding islands and the exposed continental shelf are discussed. The pollen records show that the pollen influx was quite low before 8.15 Ma and increased dramatically afterwards. The influx changes can be ascribed,on one side,to tectonics deformations around the southern SCS resulting in rapid uplift of islands and subsequent increase of the sediment rates and pollen influx and on the other side to climate cooling and monsoon enhancement. Around 2.63 Ma was another obvious boundary,the increasing of pollen and spores influx since this time was mainly related to global climate cooling. Spectrum analysis of pollen influx values shows that 2 Ma,0.67 Ma,and 0.19-0.17 Ma cycles existed during 12-3.0 Ma,while 0.1 Ma and 46.9 ka cycles existed during 3.0-2.0 Ma.  相似文献   

6.
  总被引:2,自引:0,他引:2  
The preservation and dissolution of calcium carbonate (namely calcium carbonate pump) controls the pH of seawater in global oceans by its buffer effect, and in turn plays a significant role in global changes in atmospheric CO2 concentration. The results from measured carbonate contents over the past 2 Ma at ODP Site 1143 in the South China Sea provide high-resolution records to explore the process of the calcium carbonate pump during Quaternary glacial cycles. The results indicate statistically that the highest carbonate accumulation rate leads the lightest δ^18O by about 3.6ka at transitions from glacials to interglacials, and that the strongest carbonate dissolution lags the lightest δ^18O by about 5.6 ka at transitions from interglacials to glacials. The calcium carbonate pump releases CO2 to the at mosphere atthe glacial-interglacial transitions, but transports atmospheric CO2 to deep sea at the interglacial-glacial transitions.The adjustable function of the calcium carbonate pump for the deep-sea CO3^2- concentration directly controls parts of global changes in atmospheric CO2, and contributes the global carbon cycle system during the Quaternary.  相似文献   

7.
Stable isotope of autogenous oceanic carbonate (e.g., calcite of foraminiferal shells) has become a basic tracer in paleoceanography. Oxygen isotope composi-tion (δ 18O) is generally controlled by factors, such as ice volume and water temperature, and is…  相似文献   

8.
    
Wang  Xin  Wang  DongXiao  Gao  RongZhen  Sun  DongHuai 《科学通报(英文版)》2010,55(13):1304-1310
The authors analyze the coral growth band from a colony in the northwestern South China Sea. The coral growth band can provide comprehensive environmental information on climate. The trend from the two-century-long annual density of the coral is in a good agreement with that of the global CO2 concentration. Both trends were small prior to the end of the 19th century; after that, trends became clear, more so from the 1960s to the 1990s (the end of the coral record). The overall coral density shows a steady d...  相似文献   

9.
南海表面海温异常对南海季风影响的数值模拟   总被引:6,自引:0,他引:6  
采用P-σ混合坐标系区域气候模式模拟了4-7月南海季风的爆发、演变过程,并进行了3组敏感性数值试验,研究南海表面海温异常对南海季风的影响,得到以下结论:(1)南海4月份海温异常对南海季风的爆发日期影响不大,但对季风爆发后的强度有所影响,异常增温造成南海季风增强,异常降温则南海季风减弱。(2)南海季风爆发和强度的变化与南海本身的海温变化情况有密切的关系,尤其是5月份南海海温异常。5月份南海异常增温可以使南海季风提前爆发,季风增强,南海海温异常降低时,南海季风爆发的时间推迟,季风减弱。(3)南海海温持续异常可以影响南海及中国大陆的高低空环流变化,海温持续异常增温可以使南海季风提前爆发,显地加强南海季风,并有利于南海季风向北推进,但当海温在6月份进一步持续增温时,则有利于季风维持在较南地区,阻碍季风向北发展;当海温持续异常降低时,南海季风推迟爆发,且明显减弱。  相似文献   

10.
  总被引:6,自引:0,他引:6  
The general characteristics of coastal erosion in China are described in terms of the regional geography, the form of erosion, the causes of erosion, and the challenges we are facing. The paper highlights the relationship between coastal erosion and sea level rises,storm waves and tides, and the influence of global climate changes on coastal erosion along the coastal zone of China. The response of the risk of coastal erosion in China to climate changes has obvious regional diversity. Research into and the forecasting of the effects of climate changes on coastal erosion are systemic work involving the natural environment, social economy, and alongshore engineering projects in the global system. Facing global warming and continual enhancement of coastal erosion, suggestions for basic theoretical study, prevention technology, management system assurance, and strengthening the legal system are presented here.  相似文献   

11.
晚更新世间冰期时的南海海平面   总被引:1,自引:0,他引:1  
从海蚀平面,晚更新世海积地面及其沙坝下伏的滨海相粘性土顶界高程等来看,距今约203万a的间冰段时南海高海面及其北部岸线接近现在的情况。晚更新世与全新世形成的海蚀平台类高,老,新沙坝比邻和类高,这是南海北部海岸的地貌的特色。  相似文献   

12.
    
High-resolution oxygen isotope stratigraphy of Core MD05-2901, which is located off eastern Vietnam in the western South China Sea (SCS), was established and indicated that the core spans a time period of the past 450 ka. Based on the bulk density, fractional porosity and lithogenic content of the sediments, terrigenous mass accumulation rate (TMAR) was obtained, which is 4.9-6.0 g cm^-2 ka^-1 on average during interglacial stages, higher than that during glacial stages, i.e. 1.9-5.0 g cm^-2 ka^-1, which is different from northern and southern SCS which show higher TMAR in glacial stages. By principle component analysis of grain size distribution of all the samples, two main control factors (F1 and F2) were obtained, which are responsible for about 80% variance of granularity. The contents of grain size population 1.26-2.66 μm% and 10.8-14.3 μm% which are sensible to F1 show high-frequency fluctuation, and correlate well with the summer insolation at 15^o N. They exhibit a distinct cyclicity with frequencies near 23 ka and 13 ka, in contrast to a strong frequency peak near 100 ka obtained in proxies 4.24-7.42 μm% and 30.1-43.7 μm% controlled mainly by F2. The sedimentary character of this part of the SCS was controlled by variations of input flux from two main source areas, namely the southwest and north SCS, which were transported by different circulations of surface current forced by East Asian summer monsoon and winter monsoon respectively. We believe that the East Asian summer monsoon has fluctuated with high frequency and been forced by changes in solar insolation in low latitude associated with precession and half precession, while ice-volume forcing is probably a primary factor in determining the strength and timing of the East Asian winter monsoon but with less important insolation forcing.  相似文献   

13.
  总被引:2,自引:0,他引:2  
The biogenic silica analysis was performed on 463 samples from ODP 184 Site 1143, the southern South China Sea. The results show that the opal content and MAR evidently increased between 12.3 and 5.7 Ma, which was contemporary with the high carbonate and total MARs, reflecting the high biogenic productivity in the late Miocene.This demonstrates the occurrence of the late Miocene \"Biogenie Bloom Event\" in the southern South China Sea, corresponding to the late Miocene-early Pliocene \"Biogenic Bloom Event\" in the Indian-Pacific Ocean. The increases of opal content and MAR after the middle Pleistocene (about 0.7 Ma)is inferred to result from the enhanced upwelling and nutrient supply, which was induced by the intensified monsoon circulation after the \"Mid-Pleistocene Revolution\".  相似文献   

14.
    
This paper briefly presents the progress of deep-sea pollen research in China since the beginning of ninetieths of the last Century. All the deep-sea pollen contri-butions mainly come from the South China Sea (SCS) and the East China Sea (ECS). The German-Chinese joint cruise (Sonne 95) and ODP 184 cruise initiated by Chinese scientists in the SCS provided excellent material for the deep-sea pollen research. So far a number of pollen results of 20-30 ka and million years from the SCS have been published. A couple of deep-sea pollen records from Okinawa Through of the ECS also came out. The high resolution pollen records obtained from the continuous deposits with high sedimentation rates and reliable age control of the deep-sea sediments provided a high time resolution history (hundred to millennial scales) of vegetation, environment and monsoon evolution of the pollen source areas (southern China and Japan). Spectral analysis of deep-sea pollen records from the SCS discovered orbital (100, 41, 23, 10 ka) and suborbital cyclicities(Heinrich and Dansgaard/Oscheger-O/D events) in the vegetation changes. Moreover, cross spectral analysis showed that the trend of vegetation changes in northern SCS was regulated mainly by changes of the ice volume in the Northern Hemisphere. The pollen record of the last 20 ka from the Okinawa Through of the ECS indicates that the marine environmental change lagged that on the terrestrail by about 1000 year. The asynchronous environmental changes between land and sea were probably caused by the time difference in thermohaline circulation. This study underscored the role of the deep-sea plant fossils as a bridge across the land and sea.  相似文献   

15.
  总被引:2,自引:0,他引:2  
Based on a detailed study of the radiolarian fauna, the abundance pattern of planktic foraminifera as well as on isotope and sedimentological records, the Mid-Pleistocene climate transition as a multiple transition phenomenon could be recognized at Core 17957-2 from the South China Sea. Distinct changes in the radiolarian/foraminfera ratio, the coarse fraction and the radiolarian assemblages can be related to the global climate cooling observed at the Mid-Pleistocene revolution (MPR) around 900 ka. A pronounced southward shift of the North Equatorial Current that leads to lower sea-surface temperatures in the South China Sea is documented by the shift of tropical to subtropical radiolarian assemblages at 900 ka. Increasing radiolarian abundance after the MPR can be interpreted as a result of stronger upwelling and nutrient supply. These abrupt variations could result from the northern trade wind system and East Asian monsoon circulation.  相似文献   

16.
    
Sea surface temperature over the past 450 ka was obtained by the unsaturation of molecular fossil-long chain alkenone with a resolution of about 1 ka from the western South China Sea. This is the longest temperature profile in the South China Sea at such high resolution. The U37^κ-SST results revealed similar glacial-interglacial cycles as the δ^18O profile of planktonic foraminifera, with SST variability of 23-25.5℃ for glacial and 25-28℃ for interglacial periods. The highest SST (28.4℃) was recorded at MIS5.5 and lowest SST (22.6℃) during MIS2. The SST record preceded the planktonic foraminiferal δ^18O on five glacial-interglacial transitions. Comparison of temperature records from the Southern and Northern Hemispheres indicated a more Southern Hemisphere-like pattern for the temperature variation in the SCS. Strong precession and semiprecession signals in the spectra of our SST record manifest the tropical phenomena.  相似文献   

17.
【目的】探明海洋工程材料在热带海洋环境试验站硅藻污损群落的组成变化,为研究该海域材料腐蚀、生物污损以及生物多样性提供参考。【方法】取4种材料进行全浸腐蚀试验,定期取出试片冷藏客运到青岛,用次氯酸钠法制成永久封片,在带有微分干涉显微镜下记数,并使用PRIMER 6对硅藻Shannon多样性指数、Pielou’s均匀度指数和Simpson优势度进行计算。【结果】检出污损硅藻16目24科30属61种,其中双眉藻属、菱形藻属和舟形藻属为优势类群;物种多样性指数随时间而增加;热浸锌表面硅藻群落结构变化与其他3种材料有所不同。【结论】在南海热带近岸,材料表面性质对其表面附着的污损硅藻群落有一定影响,其中锌离子的影响较为明显。  相似文献   

18.
    
《科学通报(英文版)》1990,35(13):1105-1105
  相似文献   

19.
    
The largest bivalve shell in the world, the marine bivalve, Tridacna spp., has hard and dense aragonite shells with annual or daily growth lines in its inner shell layers, and is becoming an ideal material for high-resolution paleoclimate reconstructions. However, identification of shell calcilization is necessary before using Tridacnidae as paleoclimate recorders.Five Tridacnidae specimens were collected from the South China Sea. The analysis results of X-ray diffraction (XRD), differential scanning calorimetry - thermo gravimetric analysis (DSC-TGA) and gas chromatography-mass spectrometer (GC-MS) showed that all the Tridacna spp.’s inner shells studied here are entirely made of aragonite, and shell calcilization does not occur. The main inorganic compound of the inner shells is CaCO3, with a content between 96.5%~97.2%; the content of the organic matter, such as hexadecane and 17 kinds of amino acids, is between 2.8%~3.5%. However, calcilization takes place in some outer shell layers. This study presents a method to identify the calcilization of Tridacnidae shell, and preliminarily determines composition and content in Tridacnidae shell. Results from this study provide a basis for such reconstruction using Tridacnidae shells.  相似文献   

20.
南海东部深海沉积物中孢粉与古环境研究   总被引:8,自引:0,他引:8  
通过对南海东部294站深海柱状剖面高分辨孢粉、藻类的研究,将294站从下至上划分为7个孢粉组合带,依次为:Ⅰ带:Dacrydium-Pinus-Lithocarpus-Quercus(带绿)-Cyathea-Polypoldiace;Ⅱ带:Castanopsis-Lithocarpus-Dacrydium-Quercus(常绿)-Pinus-Polypodiace;Ⅲ带:Quercus(常绿)-Castanopsis-Podocarpus-Polypodiaceae;Ⅳ带:Polypodiaceae-Cyathea-Pteris-Pinus-Gramineae;Ⅴ带:Quercus(常绿)-Podocarpus-Lithocarpus-Cyathea-Polypodiaceae;Ⅵ带:Pinus-Quercus(常绿)-Palmae-Mangrove pollen-Gramineae;Ⅶ带:Dacrydium-Palmae-Mangrove Pollen-Pinus-Cyperaceae-Cyathea.并相应恢复了南海东部地区12万年以来5个植被、气候演替阶段,依次为:炎热、湿润的热带季雨林——暖热而稍干的热带北缘半常绿季雨林——炎热、湿润的热带季雨林——暖热而稍干的热带北缘半常绿季雨林——炎热、湿润的热带季雨林。结合氧同位素测年资料,对294站地层时代划分作了讨论,为南海古气候、古环境演变研究提供了科学的证据。  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号