Timing of the late-glacial climate reversal in the Southern Hemisphere using high-resolution radiocarbon chronology for Kaipo bog, New Zealand     

Irka Hajdas  David J. Lowe  Georges Bonani 《Quaternary Research》2006,65(2):340-345

The pattern of climate change in the Southern Hemisphere during the Younger Dryas (YD) chronozone provides essential constraint on mechanisms of abrupt climate change only if accurate, high-precision chronologies are obtained. A climate reversal reported previously at Kaipo bog, New Zealand, had been dated between 13,600 and 12,600 cal yr B.P. and appeared to asynchronously overlap the YD chron, but the chronology, based on conventionally radiocarbon-dated bulk sediment samples, left the precise timing questionable. We report a new high-resolution AMS ¹⁴C chronology for the Kaipo record that confirms the original chronology and provides further evidence for a mid-latitude Southern Ocean cooling event dated between 13,800 and 12,400 cal yr B.P. (2σ range), roughly equivalent to the Antarctic Cold Reversal.  相似文献   

Abrupt climate change: An alternative view   总被引：2，自引：0，他引：2  

Carl Wunsch 《Quaternary Research》2006,65(2):191-203

Hypotheses and inferences concerning the nature of abrupt climate change, exemplified by the Dansgaard-Oeschger (D-O) events, are reviewed. There is little concrete evidence that these events are more than a regional Greenland phenomenon. The partial coherence of ice core δ¹⁸O and CH₄ is a possible exception. Claims, however, of D-O presence in most remote locations cannot be distinguished from the hypothesis that many regions are just exhibiting temporal variability in climate proxies with approximately similar frequency content. Further suggestions that D-O events in Greenland are generated by shifts in the North Atlantic ocean circulation seem highly implausible, given the weak contribution of the high latitude ocean to the meridional flux of heat. A more likely scenario is that changes in the ocean circulation are a consequence of wind shifts. The disappearance of D-O events in the Holocene coincides with the disappearance also of the Laurentide and Fennoscandian ice sheets. It is thus suggested that D-O events are a consequence of interactions of the windfield with the continental ice sheets and that better understanding of the wind field in the glacial periods is the highest priority. Wind fields are capable of great volatility and very rapid global-scale teleconnections, and they are efficient generators of oceanic circulation changes and (more speculatively) of multiple states relative to great ice sheets. Connection of D-O events to the possibility of modern abrupt climate change rests on a very weak chain of assumptions.  相似文献   

Holocene climate and cultural evolution in late prehistoric-early historic West Asia   总被引：2，自引：0，他引：2  

Michael Staubwasser  Harvey Weiss 《Quaternary Research》2006,66(3):372-387

The precipitation climatology and the underlying climate mechanisms of the eastern Mediterranean, West Asia, and the Indian subcontinent are reviewed, with emphasis on upper and middle tropospheric flow in the subtropics and its steering of precipitation. Holocene climate change of the region is summarized from proxy records. The Indian monsoon weakened during the Holocene over its northernmost region, the Ganges and Indus catchments and the western Arabian Sea. Southern regions, the Indian Peninsula, do not show a reduction, but an increase of summer monsoon rain across the Holocene. The long-term trend towards drier conditions in the eastern Mediterranean can be linked to a regionally complex monsoon evolution. Abrupt climate change events, such as the widespread droughts around 8200, 5200 and 4200 cal yr BP, are suggested to be the result of altered subtropical upper-level flow over the eastern Mediterranean and Asia.The abrupt climate change events of the Holocene radically altered precipitation, fundamental for cereal agriculture, across the expanse of late prehistoric-early historic cultures known from the archaeological record in these regions. Social adaptations to reduced agro-production, in both dry-farming and irrigation agriculture regions, are visible in the archaeological record during each abrupt climate change event in West Asia. Chronological refinement, in both the paleoclimate and archaeological records, and transfer functions for both precipitation and agro-production are needed to understand precisely the evident causal linkages.  相似文献   

基于遥感的民勤绿洲植被覆盖变化定量监测   总被引：16，自引：0，他引：16  

高志海  李增元  魏怀东  丁锋 《地理研究》2006,25(4):587-595

基于混合像元条件下的TM影像植被覆盖度遥感反演,定量研究了甘肃省民勤绿洲1987年至2001年植被覆盖时空变化的规律与特点。结果表明,15年中,民勤绿洲的植被覆盖发生了很大的变化,农田植被(耕地)面积增加了53.11%,而中、高盖度植被的面积却减少了25.21%,这对民勤绿洲的长久生态安全构成了严重的威胁。民勤绿洲植被覆盖变化的空间转化过程复杂,但总体属于开垦—植被退化型。15年中因开垦和植被退化而损失的中、高盖度植被达42204.81hm2,占原面积的81.73%,而且损失的主要是绿洲边缘的防风固沙植被,其中因开垦损失的面积为18776.08hm2,占损失面积的44.5%。超采地下水引起的地下水位快速下降是导致绿洲边缘天然和人工灌丛植被退化的主要原因。控制开垦并培育相对稳定的灌丛型植被,应该是研究区生态环境建设的重点。  相似文献   

流动人口分布与区域经济发展关系若干解释(1990、2000)   总被引：10，自引：1，他引：10  

鲁奇  王国霞  杨春悦  曾磊 《地理研究》2006,25(5):765-774

本文对我国1990、2000年间流动人口在东、中、西部和东部地区中环渤海、长江三角洲、珠江三角洲及福建三个亚区的分布变化以及这一分布变化与上述各地区各相关经济与非经济因素变化的关系进行了研究。研究发现,10年中流动人口东、中、西部分布变化与东、中、西部经济发展的变化高度一致;而10年中流动人口在东部地区环渤海、长江三角洲、珠江三角洲及福建这三个亚区层面的分布变化则与经济发展要素变化有一致的方面,也有不一致的方面。珠江三角洲及福建的经济增长带来了流动人口的大幅增长,除珠江三角洲劳动密集型企业众多外,这可能与该区域地方社会人文等文化本底所决定的经济发展制度及习俗有一定的相关性。  相似文献   

长江下游地区下蜀黄土堆积与成壤环境演变——以南京江北地区一典型剖面为例     

毛龙江  贾耀锋  邹欣庆 《地理研究》2006,25(5):887-894

通过对南京江北地区一个典型剖面（TZC剖面）进行野外调查、室内磁化率、粒度等替代性指标分析和光释光断代研究,探讨了该地区第一层古土壤形成时的粉尘堆积与成壤环境演变特点。结果表明:第一层古土壤（400⁵0cm）形成于全新世最适宜期（8500³100aBP）,是在末次冰期下蜀黄土堆积成壤基础上的再发育,与下伏黄土之间存在发生学联系。根据沉积年代和沉积厚度对沉积速率估算,该地区末次冰期沉积速率约为11.17cm/ka,而且可以推测古土壤顶部经历过强烈的水土侵蚀作用,侵蚀的厚度为98.67cm,侵蚀下来的黄土在地势低洼的地方形成次生黄土,这表明了次生黄土同为风尘成因,只是经过后期雨水的侵蚀、搬运和再堆积而已。全新世晚期3100年以来,季风转变,沙尘暴加剧,土壤退化,在南京江北地区堆积成厚约50cm左右的现代黄土层或表土层。  相似文献   

1993～2003年厦门市湿地动态变化及其驱动因素分析   总被引：1，自引：3，他引：1  

林巧莺  林广发  陈志鸿  杨陈照  游丽平 《湿地科学》2006,4(4):298-303

通过对厦门市1993年TM遥感影像和2003年ETM 遥感影像的解译分析和数据统计,从湿地面积动态变化和湿地消长情况等方面,用单一土地利用动态度等指标对1993~2003年期间厦门市的湿地变化进行了研究。结果表明,1993~2003年期间厦门市天然湿地面积减少了2103hm2,其中有954hm2(滩涂864hm2)转变为非湿地,有1149hm2转变为人工湿地;而人工湿地面积增加了2775hm2,其中养殖场面积从1993年的5778hm2迅猛增加到2003年的9768hm2,年均增长率为6.91%,水库与水塘和盐田则分别减少了961hm2和254hm2。有27.74%、11.41%、9.33%和3.63%的养殖场面积分别是由非湿地、滩涂、盐田和水库与水塘转变而来的;有54.37%的盐田转变成了养殖场,有33.24%、30.24%的红树林转变为非湿地、养殖场,有10.35%、8.64%的滩涂转变为养殖场、非湿地。对社会经济驱动因素的分析表明,经济发展、人口增长和农业生产比较利益因素极大影响着厦门市湿地的动态变化。  相似文献   

Stratigraphic evolution of a fluvial–eolian succession: The example of the Upper Jurassic—Lower Cretaceous Guará and Botucatu formations, Paraná Basin, Southernmost Brazil     

Claiton M.S. Scherer  Ernesto L.C. Lavina 《Gondwana Research》2006,9(4):475-484

The Guará and Botucatu formations comprise an 80 to 120 m thick continental succession that crops out on the western portion of the Rio Grande do Sul State (Southernmost Brazil). The Guará Formation (Upper Jurassic) displays a well-defined facies shift along its outcrop belt. On its northern portion it is characterised by coarse-grained to conglomeratic sandstones with trough and planar cross-bedding, as well as low-angle lamination, which are interpreted to represent braided river deposits. Southwards these fluvial facies thin out and interfinger with fine- to medium-grained sandstones with large-scale cross-stratification and horizontal lamination, interpreted as eolian dune and eolian sand sheets deposits, respectively. The Botucatu Formation is characterised by large-scale cross-strata formed by successive climbing of eolian dunes, without interdune and/or fluvial accumulation (dry eolian system). The contact between the Guará and the Botucatu formations is delineated by a basin-wide deflation surface (supersurface). The abrupt change in the depositional conditions that took place across this supersurface suggests a major climate change, from semi-arid (Upper Jurassic) to hyper-arid (Lower Cretaceous) conditions. A rearrangement of the Paraná Basin depocenters is contemporaneous to this climate change, which seems to have changed from a more restrict accumulation area in the Guará Formation to a wider sedimentary context in the Botucatu Formation.  相似文献   

区域生态安全动态变化及空间差异定量分析:以陕北黄土高原为例     

李晶  任志远  周自翔 《地理学报(英文版)》2006,16(2):251-256

1 Introduction Ecological security is defined as the goal of stakeholders to create a condition where the physical surroundings of a community provide for the needs of its inhabitants without diminishing its natural stock (Chen, 2002; Wachernagel et al.,…  相似文献   

青藏高原不同时段气候变化的研究综述     

李潮流  康世昌 《地理学报(英文版)》2006,16(3):337-345

1 Introduction The annual mean world temperature increased by about 0.6℃ from the late 1800s to the 1980s (Wang, 1994). The global environmental change is marked with “global warming” and its possible effects on the ecosystem as well as the production …  相似文献