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1.
南海西南部晚更新世500 ka以来的古海洋学特征 总被引：8，自引：1，他引：8
对湄公河口外MD01—2392孔浮游有孔虫的定量分析，并采用FP-12E转换函数、MAT现代类比法及温跃层转换函数的计算，结合氧同位素分析结果，揭示了南海南部晚更新世近500ka以来的古海洋学演化特征．发现冰期MIS12、MISS、MIS2-4冬季表层水温明显高出相邻的间冰期，特别是间冰期M189、MIS5、MIS1表层水温都较低．温跃层在MIS5与MIS1最浅，MIS9其次．主要表现在浮游有孔虫深层高营养种的含量增高，表明上升流增强．间冰期的低水温很可能主要是由于上升流影响所致，当然表层盐度由于多雨而降低也可能影响到间冰期的水温估算．冰期时较高的表层水温，喜暖高盐型次表层种Pulleniatina obliquiloculata的大量繁殖，说明冰期时南部海区受来自北部强冬季风的制约使上升流活动减弱，海平面降低后与邻区通道的关闭也造成水体置换明显减弱，可能有淡水盖层发育，最终导致上层海水分层增强和冬季表层水温保持相对较高．晚更新世时期的南海南部由于冰期低海平面造成半封闭的海盆环境和季风变化，是影响其浮游有孔虫对冰期旋回响应与北部和开放大洋不同的根本原因． 相似文献
2.
根据南海西部越南岸外MD05-2901岩芯成对的有孔虫壳体氧同位素和U3k7′-SST计算出过去450ka以来南海西部表层海水氧同位素～δ18Owater和盐度Swater变化记录,二者的变化范围在冰期分别为0.2‰～0.6‰和34.2‰～35.1‰,间冰期分别为-0.6‰～0和32.4‰～33.7‰,表现为冰期高、间冰期低的特征。相反扣除冰盖影响后的剩余氧同位素～δ18Oresid和剩余盐度Sresid,呈现冰期低、间冰期高的特征,在冰期分别平均为-0.5‰和32.7‰,间冰期分别平均为-0.3‰和33.1‰。研究认为该现象主要与赤道太平洋海域冰期纵向的ITCZ平均位置偏南导致的降雨增加有关,同时冰期温度低蒸发弱,间冰期温度高蒸发强以及冰期海平面下降,南海地理格局的改变、河流输入增多等因素也有一定影响。 相似文献
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4.
对比分析了太平洋(Site 806)、大西洋(Site 664)和加勒比海地区(Site 999)末次冰期最盛期和全新世钻孔顶部不同尺寸大小的浮游有孔虫Globigerinoides sacculifer(500～600μm和300～355μm)和Globi-gerinoides ruber(300～355μm和250～300μm)的硼同位素组分变化,发现个体相对较小的有孔虫样品由于受到样品量以及样品前处理过程的影响,其硼同位素在末次冰期最盛期出现异常,浮游有孔虫硼同位素分析,尤其是冰期-间冰期时间尺度上的硼同位素分析,适合用个体相对较大的有孔虫。末次冰期最盛期太平洋和加勒比海地区溶解作用可能加强,其G.sacculifer的硼同位素偏低,但G.ruber的硼同位素不受溶解作用的影响,能够反映末次冰期海水pH值的变化。三个钻孔末次冰期最盛期G.ruber的硼同位素比全新世的硼同位素平均高(1.3±1.2)‰(2s.e.),与理论预测值1.6‰一致。 相似文献
5.
孟加拉湾晚第四纪的季风气候及其古海洋学记录 总被引：4，自引：0，他引：4
分析了研究区季风的形成、演变及其控制因素 ,指出强烈的盐度对比是在北印度洋占主导地位的季风气候系统的直接反映。通过位于孟加拉湾地区的 3支岩心 MD771 81、MD771 83和MD771 69的 δ1 8O值所反映的表层海水盐度变化的分析 ,认为研究区全新世及末次冰期—间冰期氧同位素第 3期西南季风强烈 ,末次冰期最盛期氧同位素第 2期西南季风微弱。通过与阿拉伯海等地区进行对比 ,进一步证明南亚季风的主要驱动因素是周期为 2 3 ka的低纬度太阳辐射。 相似文献
6.
末次冰期旋回尤其是氧同位素3期气候明显不稳定, 南亚季风活动并不遵循冰期间冰期的规律.通过东北印度洋区位于安达曼海南部、苏门答腊岛西北端格雷特海峡的BAR9427岩心的古海洋学研究, 并与相邻孟加拉湾地区的MD77181和MD81349二支岩心进行对比分析, 认识到末次冰期氧同位素2期时, 研究区东北冬季风增强, 上升流活跃, 古生产力较高, 同时近岸地区蒸发作用强烈, 海水盐度升高.末次冰期大间冰阶氧同位素3期的早、晚期, 研究区西南夏季风活动强烈, 向东的西南季风流, 使得孟加拉湾中部盐度升高, 而北部由于季风降雨, 大量的淡水输入使得盐度大幅度下降, 且八月盐度远低于二月.西南夏季风变化遵循23ka的岁差周期, 在我国青藏高原、黄土与沙漠以及阿拉伯海等区都有表现. 相似文献
7.
海洋沉积物中的某些主微量元素与沉积物源区有着密切的联系,它们之间的比值变化受到源区化学风化强度的影响,因此这些元素的比值变化可以反映出海洋沉积物源区古气候的变化。本文研究了南海北部陆坡MD12-3432站位深海氧同位素6期和5期(MIS6/5) 沉积物的主微量元素,发现其表现出良好的气候控制变化特征,K/Ti、Mg/Ti、Al/Ti、Fe/Ti、Co/Ti、Zn/Ti和V/Ti等比值在MIS 5期时较高,而在MIS6期时较低。南海北部的碎屑物质主要来自中国华南地区,沉积物中元素比值的变化表明间冰期时(MIS5)华南地区陆壳化学风化增强,说明该时期华南陆地气候环境温暖湿润,这可能是间冰期时东亚夏季风加强的结果;而冰期时南海北部沉积物源区化学风化减弱,则与此时东亚冬季风较强,华南地区气候干燥寒冷相关。同时,与表层海水生产力相关的Ba/Ti比值在间冰期较高而冰期较低,反映出南海北部在间冰期时表层生产力较高而冰期时相对较低,这可能是由于东亚夏季风增强带来更多降雨,陆地化学风化作用加强,大量营养成分随河流进入南海,导致南海北部表层海水生产力增加。 相似文献
8.
末次冰期以来南海北部下陆坡区沉积有机质地球化学特征及其意义 总被引：1，自引：0，他引：1
选取南海北部下陆坡-深海平原过渡带典型沉积柱状样,通过对其沉积有机质的整体有机地球化学特征进行表征,探讨了南海下陆坡-深海平原区沉积有机质在冰期/间冰期旋回中的赋存状态、来源变化以及与古气候环境之间的相应关系。结果表明,总有机碳（TOC）、总氮（TN）和有机质稳定碳同位素（δ13Corg）与冰期/间冰期旋回有明显的对应关系,冰期时对应高值,间冰期时对应低值;而有机质稳定氮同位素（δ15N）表现为全新世时其值偏低,末次冰消期其值偏高,与气候旋回没有相关性; C/N值和δ13Corg值都表明南海北部下陆坡沉积有机质来源是陆相和海相的混源,且在末次冰期/间冰期尺度上主要以海相来源为主。 相似文献
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南海深水区晚更新世以来沉积速率、沉积通量与物质组成 总被引：6，自引：2，他引：6
通过调查所获得柱样沉积物氧碳同位素测年资料及多学科综合分析表明,晚更新世以来南海沉积速率和沉积通量具有以下几个特征 :(1)总体上为间冰期沉积速率低、冰期沉积速率高,冰期沉积速率是间冰期沉积速率的 1.3～ 1.6倍;(2 )南海沉积速率趋势面分析表明,氧同位素 1期东北陆坡和西南陆坡沉积速率高,氧同位素 2、3期沉积速率分布特征相似,与 1期有所不同,东北陆坡沉积速率高于西南陆坡,表明氧同位素 2期之后,南海的沉积环境发生明显的改变,造成上述沉积速率分布的主要控制因素是南海周围的河流分布、季风、海流等;(3)南海东部沉积通量与物质组成分析表明,末次冰期以来沉积总通量北部陆坡区明显高于深海区,前者是后者 2～ 3倍,并有自北向南逐渐降低的趋势;(4)硅质生物沉积通量冰期明显高于间冰期,末次冰期以来东北部陆坡区的硅质生物沉积通量最高,末次冰期之前恰好相反,深海盆高于陆坡区;(5 )末次冰期以来,陆源沉积约占南海东部海域沉积的 4 4 %以上。 相似文献
11.
The geology of the Last Interglaciation (sensu stricto, marine isotope substage (MIS) 5e) in the Bahamas records the nature of sea level and climate change. After a period of quasi-stability for most of the interglaciation, during which reefs grew to +2.5 m, sea level rose rapidly at the end of the period, incising notches in older limestone. After brief stillstands at +6 and perhaps +8.5 m, sea level fell with apparent speed to the MIS 5d lowstand and much cooler climatic conditions. It was during this regression from the MIS 5e highstand that the North Atlantic suffered an oceanographic “reorganization” about 118±3 ka ago. During this same interval, massive dune-building greatly enlarged the Bahama Islands. Giant waves reshaped exposed lowlands into chevron-shaped beach ridges, ran up on older coastal ridges, and also broke off and threw megaboulders onto and over 20 m-high cliffs. The oolitic rocks recording these features yield concordant whole-rock amino acid ratios across the archipelago. Whether or not the Last Interglaciation serves as an appropriate analog for our “greenhouse” world, it nonetheless reveals the intricate details of climatic transitions between warm interglaciations and near glacial conditions. 相似文献
12.
Henning A. Bauch Helmut Erlenkeuser Pieter M. Grootes Jean Jouzel 《Quaternary Research》1996,46(3):260-269
Climatic reconstruction of glacial to interglacial episodes from oxygen isotopes in sediment cores from the Nordic seas is complicated by strong local meltwater contributions to the oxygen isotope changes. Combination of benthic and planktic foraminiferal isotope data with foraminiferal abundances and ice-rafted debris (IRD) allows separation of local and global effects and subdivision of the marine oxygen isotope events 6.2–5.4, which include the last interglaciation, into: (1) a meltwater phase after glacial stage 6, recorded by large amounts of IRD and low foraminiferal abundance, indicating surface water warming; (2) an IRD-free period with high deposition rates of subpolar foraminifera and other CaCO3pelagic components, recognized here as the “full” interglaciation; and (3) a phase with the recurrence of IRD and the demise of subpolar species. Comparison of ice-core records and marine data implies that the global climate during the last full interglaciation and that during the postdeglacial Holocene were similar. The records show no significantly different variations in the proxy data. In contrast, the oxygen isotopes of planktic foraminifera and ice cores indicate significant differences during each of the deglacial transitions (Terminations I and II) that preceded these two interglaciations. These suggest that during Termination II the climatic evolution in the Nordic seas was less affected by abrupt changes in ocean–atmosphere circulation than during the last glacial to interglacial transition. 相似文献
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James L. Bischoff Kirsten M. Menking Jeffrey P. Fitts John A. Fitzpatrick 《Quaternary Research》1997,48(3):313-325
Chemical analyses of the acid-soluble and clay-size fractions of sediment samples (1500-yr resolution) reveal oscillations of lake salinity and of glacial advances in core OL-92 back to 155,000 yr B.P. Relatively saline conditions are indicated by the abundance of carbonate and smectite (both pedogenic and authigenic), reflected by Ca, Sr, and Mg in the acid-soluble suite, and by Cs2O, excess MgO, and LOI (loss on ignition) in the clay-size fraction. Rock flour produced during glacial advances is represented by the abundance of detrital plagioclase and biotite in the clay-size fraction, the ratio of which remains essentially constant over the entire time span. These phases are quantitatively represented by Na2O, TiO2, Ba, and Mn in the clay fraction. The rock-flour record indicates two major ice-advances during the penultimate glacial cycle corresponding to marine isotope stage (MIS) 6, no major advances during the last interglaciation (entire MIS 5), and three major advances during the last glacial cycle (MIS 2, 3, and 4). The ages of the latter three correspond rather well to36Cl dates reported for Sierra Nevada moraines. The onset of the last interglaciation is shown by abrupt increases in authigenic CaCO3and an abrupt decrease in rock flour, at about 118,000 yr B.P. according to our time scale. In contrast, the boundary appears to be gradual in the δ18O record in which the change from light to heavy values begins at about 140,000 yrs B.P. The exact position of the termination, therefore, may be proxy-dependent. Conditions of high carbonate and low rock flour prevailed during the entire period from 118,000 yr B.P. until the glacial advance at 53,000 yr B.P. signaled the end of this long interglaciation. 相似文献
14.
地处南亚季风区的沙鲁里山地区保留有丰富的第四纪冰川作用遗迹。文章通过ESR对冰碛物直接定年,结合冰碛地貌形态及其风化程度差异,结果表明沙鲁里山地区可能经历了4次规模较大的冰川作用。它们的ESR年代大约为19～16kaB.P.,48～43kaB.P.,135kaB.P.和571kaB.P.,分别与深海氧同位素第2、第3、第6、第16阶段对应。自沙鲁里山最早冰川作用(571kaB.P.)以后,该区经历了较大规模的抬升作用。MIS2和MIS4期间西南季风微弱,降水稀少,气温严寒,南亚季风区冰川发育受到一定限制。MIS3早期和晚期夏季风强盛,降水丰富,温度较高,水热平衡状况有利于冰川发育;MIS3中期气温较低,夏季风较强盛,降水较丰富,这种冷湿组合的气候条件有利于冰川发育。南亚季风区,MIS3期间的冰川前进规模不亚于甚至在某些区域超过了末次盛冰期,其主要原因可能是受制于夏季风的降水差异。 相似文献
15.
Paleorainfall Reconstructions from Pedogenic Magnetic Susceptibility Variations in the Chinese Loess and Paleosols 总被引：2，自引：0，他引：2
The rock magnetic properties of the Chinese loess and paleosols constitute a unique and sensitive record of East Asian paleoclimate through the Quaternary Period. Systematic variations in the concentration and grain size of the magnetic minerals in these sediments have produced systematic variations in the magnetic susceptibility signal, which can be easily and rapidly measured at many sites across the Loess Plateau. Variations in many other rock magnetic properties can be used to identify the key shifts in ferrimagnetic grain size, but magnetic susceptibility alone is sufficiently sensitive to record stadial and interstadial climate stages, as well as glaciations and interglaciations. Past changes in rainfall and monsoon activity for this region are reconstructed from the susceptibility variations. The susceptibility record is calibrated using the modern relationship between rainfall and pedogenic susceptibility on the Loess Plateau. Our rainfall reconstructions identify enhanced summer monsoonal activity in the Chinese Loess Plateau region in the early Holocene and the last interglaciation. In the presently semiarid western area of the plateau, annual precipitation in interglacial times was up to 80% higher than at present; in the more humid southern and eastern areas, values were up to 20% higher than today's levels. During the last glaciation, precipitation decreased across the entire plateau, typically by 25%. The relationship between pedogenic susceptibility, climate, and weathering age was examined over the Northern Hemisphere temperate zone and the observed positive correlation between rainfall and susceptibility indicates that climate, rather than soil age, is the predominant factor that controls pedogenic susceptibility enhancement in loess soils. 相似文献
16.
《China Geology》2019,2(3):315-324
The sedimentary environment and ecological system in the South Yellow Sea (SYS) changed dramatically due to sea level change caused by glacial-interglacial cycles. The authors report the use of marine biomarkers (brassicasterol, dinosterol and C37 alkenones) and terrigenous biomarkers (C28+C30+C32 n-alkanols) in core DLC70-3 from the SYS to reconstruct the variation in the phytoplankton productivity and community structure and possible mechanisms during the middle Pleistocene. The results show that the primary productivity and that of single algae presented a consistent trend for the whole core during the middle Pleistocene, which was high during interglacial periods and low during glacial periods, with the highest being in marine isotope stage (MIS) 5–9 and MIS 19–21. The main reason is that the Yellow Sea Warm Current (YSWC) carried much of high temperature, high salinity water into the SYS, causing upwelling and vertical mixing and stirring, which increased the nutrient supply in the photosynthetic layer. The phytoplankton community structure mainly showed an increase in the relative content of haptophytes in MIS 5–9 and MIS 19–21, while the relative content of diatoms and dinoflagellates decreased; there was no evidence for a haptophyte content in other stages. The results reveal a shift from a coccolitho-phorid-dominated community during MIS 5 –9 and MIS 19 –21 to a diatom-dominated community during the other stages, mainly as a result of surface salinity variation, attributed to the invasion of the YSWC during high sea level periods. 相似文献
17.
We reconstructed the paleoenvironmental history of surface and deep water over the last 130 kyr from oxygen and carbon isotope ratios of planktonic and benthic foraminifera in two cores (MD179-3312 and MD179-3304) from the Joetsu Basin, eastern margin of the Japan Sea. Our data showed that paleoceanographic changes such as influx of surface currents and vertical circulation were associated with global glacial–interglacial sea level change. Surface water conditions were influenced by the influx of Tsushima Current, East China Sea coastal or off-shore waters through the Tsushima Strait during interglacial or interstadial stages, and strongly affected by freshwater input during the glacial maximum. During interglacial maximums such as Marine Isotope Stages 1 and 5e, development of well-oxygenated bottom water was indicated. A density-stratified ocean with weak ventilation was inferred from the isotopic records of benthic foraminifera during the Last Glacial Maximum. Local negative excursions in carbon isotopes during deglacial or interglacial periods may suggest the dissolution of gas hydrates or methane seep activities. 相似文献
18.
南海北部晚第四纪高分辨率浮游氧同位素地层学及其古气候信息 总被引：1，自引：0，他引：1
对南海北部MD05-2904孔45 m的连续沉积物中提取的浮游有孔虫Globigerinoides ruber(白色)进行稳定同位素分析, 得到晚MIS 8以来(时间跨度257 ka, 平均时间分辨率228 a)的高分辨率沉积记录, δ18O和δ13C的频谱分析显示了强烈的岁差(23.4 ka、19.8 ka)、半岁差(11.7 ka、9.9 ka)周期.MD05-2904孔MIS 24时间段的氧同位素记录了格陵兰冰心中发现的Dansgaard/Oeschger和Heinrich事件.与葫芦洞石笋记录及南海邻区浮游有孔虫氧同位素记录的对比显示了受季风控制的区域因素, 如降雨、河流输入导致的盐度变化等对表层海水组成的影响.氧同位素在MIS 3、MIS 6的早期以及MIS 7.4偏轻; 而在MIS 5.5偏重, 这种现象解释为降雨量和蒸发量共同作用的结果.而末次冰盛期高达6570 cm/ka的沉积速率反映了低海平面时孔位离岸距离缩短带来丰富的沉积物源. 相似文献
19.
中国西部山岳冰川MIS3b冰进的初步探讨 总被引：6，自引：5，他引：1
对横断山的沙鲁里山、祁连山东段的冷龙岭、天山西段托木尔峰南麓的阿特奥依纳克河流域等3个地区7个研究点的第四纪冰川作用开展了深入研究,应用ESR测年技术在7个研究点特定的地貌部位共获得12个对应于MIS3(56~36 ka BP)的测年结果,且年龄基本上都对应于MIS3b(54~44 kaBP).结合已有的研究资料,并对MIS3气候特征进行综合分析,研究表明:MIS3强大的季风环流带来的丰富降水与MIS3b冷阶段的组合是川西高原的沙鲁里山与祁连山东段冷龙岭MIS3b冰进的主要原因,而天山西段阿特奥依纳克河流域MIS3b冰进则是不稳定的西风波动带来的丰富降水所致.这3个地区沉积有该次冰进的冰碛物. 相似文献