共查询到20条相似文献，搜索用时 62 毫秒
1.
神农架140～124 kaBP百年尺度东亚季风降水的石笋记录 总被引：3，自引：2，他引：3
基于神农架山宝洞SB28石笋230Th年龄和氧同位素数据,建立了140~124 kaBP百年尺度的东亚季风降水序列,其长期演化趋势与北纬33°夏季日辐射能量曲线基本一致。山宝洞SB28石笋与董哥洞D4石笋δ18O曲线呈现出整体一致的特征,证实了亚洲季风降水同位素组成变化具有广泛的区域意义。末次间冰期129.5~124.3kaBP季风降水具有百年尺度高频振荡特征,功率谱分析周期有525、228和207 a,类似于全新世大气△14C残差百年尺度周期,表明末次间冰期亚洲季风强度的变化仍然受太阳活动的影响。在倒数第二次冰期向末次间冰期转换时,北半球太阳辐射可能触发了全球末次间冰期全盛期的开始。 相似文献
2.
本溪王家崴洞10500～5000aBP石笋记录及区域气候意义 总被引：3，自引：0，他引：3
基于典型东亚季风区辽宁省本溪市2支石笋样品(W6与W4),通过9个230 Th年龄和386个氧同位素数据,重建了10 500～5 000aBP期间平均分辨率为12～34a的氧同位素时间变化序列。研究时段石笋δ18 O相对振幅为2.0‰,在平均值约-8.5‰上下波动,指示了早全新世东亚季风强度的长期趋势变化和百年尺度振荡信息。相同时段本溪王家崴洞、湖北三宝洞、贵州董哥洞石笋δ18 O记录对比结果表明,全新世石笋δ18 O长期增加趋势类似于北半球太阳辐射能量变化曲线,但东北地区石笋δ18 O大约在10 500a已达到最大值,早于长江流域以南地区约1 000a,这可能表明全新世亚洲季风降水并不同步变化,可能与热带、亚热带季风系统差异响应于区域大气环流有关。功率谱分析W6石笋δ18 O时间序列发现其存在显著的225和91a的周期,与树轮Δ14 C周期(208和88a)基本一致,揭示了中全新世百年尺度东亚季风变化可能主要响应于太阳活动。 相似文献
3.
《海洋地质与第四纪地质》2010,(4)
基于湖北神农架犀牛洞石笋(SN)21个230Th年龄及486个δ18O数据,建立了近2000年来平均分辨率4～5a的δ18O时间序列。该记录显示,近两千多年来东亚夏季风强度总体呈逐步减弱趋势,并叠加数次数十年到百年尺度的振荡旋回,中世纪暖期及小冰期显示独特特征。石笋δ18O曲线与北半球(33°N)太阳辐射曲线一致,揭示了近2000a来亚洲季风变化主要受控于太阳辐射的变化。通过与历史气候记录对比发现,汉朝和唐朝对应δ18O偏负即相对稳定的气候阶段,而三国、两晋、南北朝、宋朝及明朝均对应于正偏且波动较大的δ18O值,存在旱涝灾害频繁交替现象,说明朝代的兴衰更替在一定程度上和气候变化存在某种联系。 相似文献
4.
基于山西龙洞8个铀钍年代和100个氧同位素数据(δ~(18 )O)重建了深海氧同位素(MIS)3阶段以来东亚夏季风演化历史。石笋L8沉积并不连续,主要生长在58.0~54.5,27.1~18.0和6.8~3.9kaBP 3个阶段。不同于季风边缘区其他洞穴记录,石笋δ~(18 )O值在24.5kaBP突然增加1‰,表明MIS2早期内陆地区经历了一次显著的弱季风过程,可能响应于北大西洋Heinrich 2事件。石笋δ~(18 )O序列伴随着轨道尺度太阳辐射的变化,晚全新世δ~(18 )O值持续偏重意味着低纬热带辐合带逐步南移,导致北方地区夏季风降水持续减少。Dansgaard-Oeschger(D-O)15事件具有明显的双峰结构,与格陵兰冰心记录的亚千年尺度温度波动几乎同步变化。 相似文献
5.
据湖北青天洞和南京葫芦洞石笋9个230Th年龄和430个δ18O测试数据,建立了18.4～14.4 kaBP平均分辨率7～8 a的东亚季风时间序列.在共同生长时段(17.5～16和18.4～17.5 kaBP),两个洞穴石笋给出了数十年尺度几乎完全一致的δ18O信号,证明了石笋δ18O记录可靠地反映了大尺度区域性季风环流及其水气同位素分馏变化.17.7和16.1 kaBP左右,石笋δ18O值明显正偏,振幅达2‰,指示两次显著的弱夏季风事件,与北大西洋冰漂碎屑事件H1b和H1a同步发生,可视为东亚季风气候系统对北大西洋H1事件的一种响应,18.3～17.7 kaBP期间,东亚季风区存在强季风降水事件,平均强度相当于Bφlling暖期的1/2,最湿润时甚至接近于Bφlling暖期降水强度,可能与北大西洋经向翻转环流的强度变化有关,这一强降水事件内部干湿旋回变化周期与Gleissberg太阳活动周期极为吻合. 相似文献
6.
末次冰盛期是末次冰期以来地球表面最寒冷的时期。通过对山东半岛地下画廊溶洞石笋DXHL3进行高精度230Th定年和高分辨率氧-碳稳定同位素分析，重建了该地区23.2～18.8 ka时期高分辨率夏季风气候环境变化历史。结果发现，山东半岛末次冰盛期夏季风气候存在显著的千年尺度波动；REDFIT分析表明，氧、碳同位素值均存在显著的2.2 ka周期。末次冰盛期山东半岛总体处于冷干状态，具体又可细分为4个阶段，即冷干（23.2～22 ka）-相对暖湿（22～21 ka）-冷干（21～19 ka）-相对暖湿（19～18.8 ka）。石笋DXHL3的δ18O变化趋势总体上与亚洲季风区内其他石笋记录相似，也与西太平洋暖池婆罗洲的石笋记录类似。这反映了末次冰盛期西太平洋暖池气候环境变化可能对山东半岛的夏季风气候变化产生了重要影响，推测西太平洋暖池表层海水温度变化引起的大气环流和黑潮的变化，是将气候环境变化信号从低纬地区传递到中高纬地区的纽带。 相似文献
7.
57～48万年前东亚夏季风的神农架石笋记录 总被引：2，自引：0，他引：2
应用MC-ICP-MS和MAT-253质谱技术,实测神农架山宝洞一支长达1.2 m石笋(SB32)的3个230Th年龄和236个氧同位素数据。在年龄误差范围内,运用天文轨道调谐方法重建了570~480 kaBP时段百年至千年际分辨率东亚夏季风降水记录。该记录跨越4个完整的岁差旋回,在岁差周期上石笋δ18O平均振幅达4‰。研究时段内东亚夏季风轨道尺度变化仍然受太阳辐射的控制。石笋记录的深海氧同位素阶段MIS14/13转换过程与末次冰消期具有类似特征。一系列千年尺度事件叠加在岁差周期夏季风变化趋势上,表明千年尺度气候变化是地球气候系统内部自我维持的固有频率,可能属于海-陆-气相互作用的结果。 相似文献
8.
湖北神农架青天洞QT17石笋的3个U-Th年龄和持续1440a的纹层计数序列提供了13.5～12.1kaBP期间平均4a分辨率的δ18O东亚季风强度记录。该记录与Cariaco盆地纹泥灰度记录显示阿勒罗德至新仙女木早期气候呈现低幅振荡特征,而格棱兰GISP2和GRIP冰心温度记录在同时段则呈现大幅高频振荡。4个记录的气候转型时间在测年误差范围内基本一致,一定程度上说明北半球高低纬千年尺度气候事件同步变化。然而,该期间东亚季风气候转型持续时间近550a(纹层计数年),而大西洋气候记录仅有230～400a,可能由于季风气候降水同位素部分受来自海洋水源同位素的影响。 相似文献
9.
贵州白骨洞石笋记录的全新世季风气候演化与突变 总被引：8，自引：0，他引：8
通过对贵州白骨洞BG1石笋13个230Th年龄的测试和390个氧同位素数据的分析,建立了12.8~3.3kaBP数十年尺度的亚洲季风降水序列,其长期演化趋势与北纬33°夏季日辐射能量曲线基本一致。石笋δ18O记录指示10.5~5.8 kaBP为本区气候湿润期,此后进入季风降水衰退期。在12.8~10.1 kaBP时段,平均分辨率为37 a的石笋降水记录与格陵兰冰心气温记录具有良好对应关系:(1)两者在新仙女木事件(YD)的变化细节及突变特征上表现出良好的一致性;(2)由YD事件向全新世转换的过程中两者都表现为3个阶梯式上升阶段,这种一致性有可能说明热带海气耦合驱动了北半球气候突变事件。在7.0~3.3 kaBP时段,平均分辨率为15 a的石笋δ18O序列记录了5次较为显著的降水减少期,可分别对应于冰心记录中的5个冷事件,高低纬气候的相似性可部分归因于太阳活动的影响。 相似文献
10.
《海洋地质与第四纪地质》2018,(6)
西沙石岛的风成碳酸盐岩是东亚季风末次冰期的产物,以砂丘与古土壤二元旋回的形式记录了东亚季风气候的干湿变化。利用西石2井钻井岩芯资料结合石岛野外地质剖面的详细考察,对石岛风成沉积序列进行了重新的地层划分,将石岛风成沉积分为三层砂丘与两层古土壤的沉积组合。通过对测年数据及东亚季风末次冰期气候变化特征的分析,认为石岛末次冰期风成沙丘与古土壤记录与黄土高原L1黄土的5个次级气候阶段一一对应,都是对东亚季风末次冰期气候背景下,气候干、湿变化在岁差尺度的沉积响应,是具有稳定周期的气候旋回。 相似文献
11.
Arne Schnack-Friedrichsen Angela M. Davis Jim D. Bennell Dei G. Huws 《Marine Georesources & Geotechnology》2001,19(4):221-243
The interdependence between the seismo-acoustic properties of a marine sediment and its geotechnical/physical parameters has been known for many years, and it has been postulated that this should allow the extraction of geotechnical information from seismic data. Though in the literature many correlations have been published for the surficial layer, there is a lack of information for greater sediment depths. In this article, a desktop study on a synthetic seafloor model illustrates how the application of published near-surface prediction equations to subsurface sediments (up to several tens of meters burial depth) can lead to spurious predictions. To test this further, acoustic and geotechnical properties were measured on a number of sediment core samples, some of which were subjected to loading in acoustically-equipped consolidation cells (oedometers) to simulate greater burial depth conditions. For low effective pressures (representing small burial depths extending to around 10 meters subsurface), the general applicability of established relationships was confirmed: the prediction of porosity, bulk density, and mean grain size from acoustic velocity and impedance appears generally possible for the investigated sedimentary environments. As effective pressure increases through, the observed relationships deviate more and more from the established ones for the near-surface area. For the samples tested in this study, in some instances increasing pressure even resulted in decreasing velocities. There are several possible explanations for this abnormal behavior, including the presence of gas, overconsolidation, or bimodal grain size distribution. The results indicate that an appropriate depth correction must be introduced into the published prediction equations in order to obtain reliable estimates of physical sediment properties for greater subsurface depths. 相似文献
12.
Shigehisa Nakamura 《Marine Geodesy》2000,23(1):55-61
Specific properties of the interannual sea level variations and annual tides in the Northwestern Pacific were studied. Several tide stations were monitored. The monthly mean sea level for the year of 1995 was analyzed at each tide station. A seismic event in 1995, some tectonic activity around the subject area, and the Kuroshio (the oceanic western boundary current) may possibly contaminate results which would have occurred from the astronomical annual tide alone. 相似文献
13.
The effect of different fixation and storage protocols on the flow cytometric (FCM) simultaneous analysis of bacterioplankton and phytoplankton in coastal seawater samples (Mediterranean coastal lagoons) was investigated. FCM measurements (cell number, fluorescence and scatter characteristics) were obtained through DAPI staining. Three fixatives [glutaraldehyde (GA), formaldehyde (FA) and paraformaldehyde (PFA)] and two storage (3 months duration) methods (5 °C and −196 °C) were tested. Two dominant populations were detected in studied samples: bacteria and eukaryotic picophytoplankton. Adding fixatives (2% final concentration) appears necessary to obtain FCM exhaustive counts of all the bacteria and phytoplanktonic cells. This was related to the permeation effect of fixatives which allowed a better DAPI staining of the cells. Maximum fluorescence, i.e. optimal staining of the cells was obtained with FA or PFA, and significant lower fluorescences with GA. Fixed samples stored at 5 °C induced rapid cell loss. Only storage in liquid nitrogen of samples fixed with FA or PFA, allows mid-term (≥4 months) preservation of bacteria or picophytoplankton cell numbers, and limited evolution of DAPI-induced fluorescence and scatter characteristics. 相似文献
14.
15.
《海洋学报(英文版)》2014,(9):F0003-F0003
<正>Acta Oceanologica Sinica(AOS)is a comprehensive academic journal edited by the Editorial Committee of Acta Oceanologica Sinica and is designed to provide a forum for important research papers of the marine scientific community which reflect the information on a worldwide basis.The journal publishes scholarly papers on marine science and technology,including physics,chemistry,biology, 相似文献
16.
The relationship between the flux of exotic benthic foraminiferal tests (i.e. tests which are supplied from open-sea sources alone) in a tidal inlet and that of bulk sediment was analysed, which can be expressed as two first-order linear equations. According to this relationship, in order to determine net sediment transport directions in the entrance, the test concentration in surficial sediments of the tidal basin can be compared against a ‘ critical level ’. The critical level is determined for the conditions that no net transport of bulk sediment is present within the entrance. If the observed concentration (averaged over the tidal basin) is higher than the simulated critical level, then the net sediment transport is directed to landward. This method is applied to the analysis of net sand transport at Christchurch Harbour, a tidal inlet system located in southern England. In this investigation, concentrations of exotic foraminiferal tests in the surficial sediments of the tidal basin and ebb tidal delta area were obtained from the analysis of sea-bed sediment samples. A series of probable critical levels were calculated based upon the data sets with regard to: (1) sediment discharge from the rivers; (2) magnitude of sediment discharge within the entrance during the ebb; (3) the test concentration outside the harbour; (4) the thickness of the moving layer; and (5) two parameters associated with dispersive processes. The results show that the concentration in the tidal basin sediment is higher than a number of simulated critical concentrations for representative cases. Consequently, the high level of the concentration of exotic benthic foraminiferal tests within the harbour should be explained as a result of landward net transport of sands within the entrance. 相似文献
17.
18.
Rahul Sharma 《Marine Georesources & Geotechnology》2000,18(3):237-250
Observations on seafloor features from subbottom profiling and seabed photography data show that the undisturbed and natural conditions before the benthic disturbance undergo a substantial change after operation of the disturber. The effects can be seen in the form of deep trenches and grooves, formed by the action of the sleds and the pumping of the sediment along its path, as well as sediment piles on either side of the track. Biological traces such as fecal coils, casts, tubes, burrows, and trails get obliterated in the areas of disturbance and resedimentation. The smooth, uniform nature of the seafloor observed in predisturbance phase shows microtopographic changes in and around the disturbed area as a result of sediment excavation and resettlement. Vertical mixing as well as lateral transport of sediment alter the geological, biological, physical, and chemical conditions on the seafloor, which need to be monitored over time to assess the process and the time taken for restoration of environmental conditions. 相似文献
19.
Vance P. Vicente 《Marine Ecology》1989,10(2):179-191
Abstract. Long-term changes in the distributional patterns of commercial sponges ( Spongia spp. and Hippospongia spp.) within the West Indian Region indicates that: 1) commercial sponges had a widespread distribution throughout the whole West Indian Region and were ubiquitous in very shallow water until about the first half of the present century; 2) they were fished commercially not only in the traditional northern Caribbean sites (Florida, Gulf of Mexico, Bahamas) but also in the Greater ( e. g. , Hispaniola, Jamaica) and Lesser Antilles; and 3) they became extinct throughout most of the Lesser Antilles ( e. g. , Puerto Rico, Vieques, St. Thomas) sometime during the first half of this century. Mortalities of spongiids within the Antilles were found to differ from other marine mortalities in that: 1) species disappeared from a large region; 2) species vanished from different habitats and depths; and 3) natural populations never recovered. Species richness patterns suggest that commercial sponge genera ( Spongia and Hippospongia ) evolved under slightly cooler elimatic conditions than those found at present, and that these extinctions occurred as a direct or indirect effect of positive thermal anomalies in sea surface and atmospheric temperatures between 1900–1950. The concept that species diversity is stable on a regional scale is questioned. 相似文献
20.
The behaviour of an axially pre-loaded cylindrical member of an offshore structure, hit by a supply ship, has been investigated. The effects of axial pre-loading on the dynamic properties of members, the extent of damage and propagation of dynamic instability in the tubular members have also been investigated. Numerical models have been validated using available experimental data from the literature although these are mostly static with no pre-loading. Axial pre-loading was found to change the dynamic characteristics of some cylindrical members quite dramatically while it had no significant effect on others. The study examined whether there was any change in the behaviour between local and global modes when the loading was dynamic rather than static. The effect of damping on the dynamic instability of axially pre-loaded tubes under lateral dynamic loads was also studied. It was observed that for some geometries the quasi-static response can be used to define the boundary between bounded and unbounded dynamic responses. The main contribution of this study, compared with previous investigations reported in the literature, is that both pre-loading and dynamic effects have been included. 相似文献