Early Holocene water budget of the Nakuru-Elmenteita basin, Central Kenya Rift     

Miriam Dühnforth  Andreas G. N. Bergner  Martin H. Trauth 《Journal of Paleolimnology》2006,36(3):281-294

The Nakuru-Elmenteita basin in the Central Kenya Rift, contains two shallow, alkaline lakes, Lake Nakuru (1770 m above sea level) and Lake Elmenteita (1786 m). Ancient shorelines and lake sediments at 1940 m suggest that these two lakes formed a single large and deep lake as a result of a wetter climate during the early Holocene. Here, we used a hydrological model to compare the precipitation–evaporation balance during the early Holocene to today. Assuming that the Nakuru-Elmenteita basin was hydrologically closed, as it is today, the most likely climate scenario includes a 45% increase in mean-annual precipitation, a 0.5°C decrease in air temperature, and an increase of 9% in cloud coverage from the modern values. Compared to the modeling results from other East African lake basins, this dramatic increase in precipitation seems to be unrealistic. Therefore, we propose a significant flow of water from the early Holocene Lake Naivasha in the south towards the Nakuru-Elmenteita basin to compensate the extremely negative hydrological budget of this basin. Since we did not find any field evidence for a surface connection, as often proposed during the last 70 years, the hydrological deficit of the Nakuru-Elmenteita basin could have also been compensated by a subsurface water exchange.  相似文献   

苏南直溪桥盆地早第三纪地层孢粉组合及地质意义     

邱祖林 《江苏地质》1999,23(4):216-220

江苏早第三纪地层 ,大部分隐埋于地下 ,对其研究 ,只能依据大量钻孔资料 ,分歧意见较多。通过对直溪桥盆地钻孔中系统孢粉资料的全面分析对比 ,来确定该地区的地层层序及时代归属 ,从而阐明早第三纪时期的古气候及古环境  相似文献   

Abrupt climate changes: from the past to the future – a review     

T. F. Stocker 《International Journal of Earth Sciences》1999,88(2):365-374

 A review of climatic variability is given with a focus on abrupt changes during the last glacial. Evidence from palaeoclimatic archives suggests that these were most likley due to reorganisations of the atmosphere–ocean system. The mechanisms responsible for these changes are presented. Their implication for future climate changes is discussed in light of recent climate model simulations. Received: 24 June 1998 / Accepted: 27 November 1998  相似文献   

近千年来内蒙古岱海气候环境演变的湖泊沉积记录   总被引：46，自引：11，他引：35  

曹建廷  王苏民  沈吉  张振克 《地理科学》2000,20(5):391-396

内陆封闭湖泊是气候环境变化的敏感指示计。通过对内蒙古岱海湖泊岩芯的有机碳同位素、总有机碳、碳酸盐含量和磁化率等多环境指标的综合分析,结合Ｐｂ－２１０测定的沉积速率,讨论了岱海地区近千年来的气候环境演化过程。揭示了本区现代小冰期的前期冷湿,后期冷干的气候特征。记录的最后两次冷期与根据冰芯、树轮、历史文献重建的１０年平均温度推得的１４５０’ｓ～１５１０’ｓ、１７９０’ｓ～１８９０’ｓ两次冷期极相吻合。  相似文献   

Record of Late Pleistocene Glaciation and Deglaciation in the Southern Cascade Range. I. Petrological Evidence from Lacustrine Sediment in Upper Klamath Lake, Southern Oregon     

Richard L. Reynolds  Joseph G. Rosenbaum  Josh Rapp  Michael W. Kerwin  J. Platt Bradbury  Steven Colman  David Adam 《Journal of Paleolimnology》2004,31(2):217-233

Petrological and textural properties of lacustrine sediments from Upper Klamath Lake, Oregon, reflect changing input volumes of glacial flour and thus reveal a detailed glacial history for the southern Cascade Range between about 37 and 15 ka. Magnetic properties vary as a result of mixing different amounts of the highly magnetic, glacially generated detritus with less magnetic, more weathered detritus derived from unglaciated parts of the large catchment. Evidence that the magnetic properties record glacial flour input is based mainly on the strong correlation between bulk sediment particle size and parameters that measure the magnetite content and magnetic mineral freshness. High magnetization corresponds to relatively fine particle size and lower magnetization to coarser particle size. This relation is not found in the Buck Lake core in a nearby, unglaciated catchment. Angular silt-sized volcanic rock fragments containing unaltered magnetite dominate the magnetic fraction in the late Pleistocene sediments but are absent in younger, low magnetization sediments. The finer grained, highly magnetic sediments contain high proportions of planktic diatoms indicative of cold, oligotrophic limnic conditions. Sediment with lower magnetite content contains populations of diatoms indicative of warmer, eutrophic limnic conditions. During the latter part of oxygen isotope stage 3 (about 37–25 ka), the magnetic properties record millennial-scale variations in glacial-flour content. The input of glacial flour was uniformly high during the Last Glacial Maximum, between about 21 and 16 ka. At about 16 ka, magnetite input, both absolute and relative to hematite, decreased abruptly, reflecting a rapid decline in glacially derived detritus. The decrease in magnetite transport into the lake preceded declines in pollen from both grass and sagebrush. A more gradual decrease in heavy mineral content over this interval records sediment starvation with the growth of marshes at the margins of the lake and dilution of detrital material by biogenic silica and other organic matter.  相似文献   

柴达木盆地昆特依盐湖磁化率特征及古气候意义   总被引：2，自引：1，他引：1       下载免费PDF全文

曾方明  向树元 《盐湖研究》2017,25(1):1-7

昆特依盐湖是柴达木盆地盐湖演化和古气候研究的重要对象。前人对昆特依盐湖钻孔的年代学和地球化学组成特征开展过一些研究,但由于采样间距大,限制了对成盐演化过程的深入理解。目前关于昆特依盐湖磁化率特征的研究尚未见报道。对昆特依盐湖ZK1402钻孔(35 m深)的14C年代和磁化率进行了初步研究。结果表明:1)钻孔由含盐碎屑层和盐层的互层所组成。盐层的低频磁化率值低,含盐碎屑层的低频磁化率值高。低频磁化率清晰地记录到古盐湖经历了4次显著的成盐期。钻孔的低频磁化率和高频磁化率的变化极为相似。2)低频磁化率和频率磁化率(百分比形式)呈负相关关系。3)钻孔9.6 m深处的加速器质谱(AMS)14C校正年代为23 333±255 cal a BP,24.8 m深处的年代为31 780±442 cal a BP,33.0 m深处的年代(19 259±207 cal a BP)出现倒转。钻孔24.8 m和33.0 m深处的14C年龄可能被低估。  相似文献   

The Pleistocene evolution of the East Antarctic Ice Sheet in the Prydz bay region: stable isotopic evidence from ODP Site 1167     

Kevin M. Theissen  Robert B. Dunbar  Alan K. Cooper  David A. Mucciarone  Dirk Hoffmann 《Global and Planetary Change》2003,39(3-4):227-256

Ocean Drilling Program Leg 188, Prydz Bay, East Antarctica is part of a larger initiative to explore the Cenozoic history of the Antarctic Ice Sheet through direct drilling and sampling of the continental margins. In this paper, we present stable isotopic results from Ocean Drilling Program (ODP) Site 1167 located on the Prydz Channel Trough Mouth Fan (TMF), the first Antarctic TMF to be drilled. The foraminifer-based δ¹⁸O record is interpreted along with sedimentary and downhole logging evidence to reconstruct the Quaternary glacial history of Prydz Bay and the adjacent Lambert Glacier Amery Ice Shelf System (LGAISS). We report an electron spin resonance age date of 36.9±3.3 ka at 0.45 m below sea floor and correlate suspected glacial–interglacial cycles with the global isotopic stratigraphy to improve the chronology for Site 1167. The δ¹⁸O record based on planktonic (Neogloboquadrina pachyderma (s.)) and limited benthic results (Globocassidulina crassa), indicates a trend of ice sheet expansion that was interrupted by a period of reduced ice volume and possibly warmer conditions during the early–mid-Pleistocene (0.9–1.38 Ma). An increase in δ¹⁸O values after 900 ka appears to coincide with the mid-Pleistocene climate transition and the expansion of the northern hemisphere ice sheet. The δ¹⁸O record in the upper 50 m of the stratigraphic section indicates as few as three glacial–interglacial cycles, tentatively assigned as marine isotopic stages (MIS) 16–21, are preserved since the Brunhes/Matuyama paleomagnetic reversal (780 ka). This suggests that there is a large unconformity near the top of the section and/or that there may have been few extreme advances of the ice sheet since the mid-Pleistocene climate transition resulting in lowered sedimentation rates on the Prydz Channel TMF. The stable isotopic record from Site 1167 is one of the few available from the area south of the Antarctic Polar Front that has been linked with the global isotopic stratigraphy. Our results suggest the potential for the recovery of useful stable isotopic records in other TMFs.  相似文献   

二叠纪—三叠纪古气候研究进展——泛大陆巨型季风气候:形成、发展与衰退   总被引：2，自引：0，他引：2  

钱利军  时志强  欧莉华 《海相油气地质》2010,15(3)

巨型季风是指二叠纪—三叠纪期间泛大陆上存在的强烈季节风,它的形成与泛大陆的形状、海陆分布及大陆的纬向分布密切相关。从晚石炭世泛大陆的聚合至晚侏罗世—早白垩世泛大陆裂解,巨型季风经历了形成、发展到衰退的过程。在三叠纪,泛大陆很大且几乎关于赤道对称,巨型季风达到最大强度。它对古气候、古环境、古生物及沉积等都产生了深刻的影响,使泛大陆低纬度地区呈现出干旱和潮湿交替的气候特征,蒸发岩和红层广泛分布;高纬度地区温暖潮湿,煤层大量分布;科罗拉多高原(美国西部)、西特提斯(欧洲)和东特提斯(中国)等地的二叠纪—三叠纪沉积地层也显示了受巨型季风影响的特征。  相似文献   

Postglacial vegetation history of Mitkof Island, Alexander Archipelago, southeastern Alaska     

Thomas A. Ager  Paul E. Carrara  Victoria Anne  Joni Johnson 《Quaternary Research》2010,73(2):259-462

An AMS radiocarbon-dated pollen record from a peat deposit on Mitkof Island, southeastern Alaska provides a vegetation history spanning ∼12,900 cal yr BP to the present. Late Wisconsin glaciers covered the entire island; deglaciation occurred > 15,400 cal yr BP. The earliest known vegetation to develop on the island (∼12,900 cal yr BP) was pine woodland (Pinus contorta) with alder (Alnus), sedges (Cyperaceae) and ferns (Polypodiaceae type). By ∼12,240 cal yr BP, Sitka spruce (Picea sitchensis) began to colonize the island while pine woodland declined. By ∼11,200 cal yr BP, mountain hemlock (Tsuga mertensiana) began to spread across the island. Sitka spruce-mountain hemlock forests dominated the lowland landscapes of the island until ∼10,180 cal yr BP, when western hemlock (Tsuga heterophylla) began to colonize, and soon became the dominant tree species. Rising percentages of pine, sedge, and sphagnum after ∼7100 cal yr BP may reflect an expansion of peat bog habitats as regional climate began to shift to cooler, wetter conditions. A decline in alders at that time suggests that coastal forests had spread into the island's uplands, replacing large areas of alder thickets. Cedars (Chamaecyparis nootkatensis, Thuja plicata) appeared on Mitkof Island during the late Holocene.  相似文献   

基于贝叶斯模型的器测、古气候重建与气候模拟数据的融合试验     

余君  李庆祥  张同文  徐文慧  张雷  崔妍 《气象学报》2018,76(2):304-314

气象部门馆藏的西部最早的器测气象资料始于20世纪30年代,不能满足建立20世纪以来中国气候变化序列的需求,而古气候重建或气候模拟资料则可以延伸到器测时代以前。为了探讨长序列多源气候资料序列融合方法,采用贝叶斯方法对中国北疆地区8条树轮气温重建资料、器测资料与国际耦合模式比较计划第5阶段（CMIP5）模式模拟资料进行了融合试验。首先利用器测资料对气温代用资料进行校验与网格重建,并以此作为贝叶斯模型的先验分布,然后,用泰勒图选出了该区域气候模拟效果最佳的几个模式;最后将网格重建和气候模拟序列用贝叶斯模型进行了融合试验。结果表明,贝叶斯融合模型能有效提取各种数据来源的有用信息进行融合,融合结果的长期变化（线性）趋势更接近器测气候序列,并在一定程度上提高了序列的精度,减小了结果的不确定性;并且,融合结果能够纠正先验分布及气候模拟数据的明显偏差,为长年代气候序列重建提供了一个可行的思路。   相似文献