Seasonal temperatures for the past ∼400 years reconstructed from diatom and chironomid assemblages in a high-altitude lake (Lej da la Tscheppa,Switzerland)     

Lucien von Gunten  Oliver Heiri  Christian Bigler  Jacqueline van Leeuwen  Carlo Casty  André F. Lotter  Michael Sturm 《Journal of Paleolimnology》2008,39(3):283-299

We analysed a 42 cm long sediment record from Lej da la Tscheppa, a high-altitude lake (2,616 m a.s.l.) in the Upper Engadine valley (Switzerland) for subfossil diatoms, chironomids and pollen. The chronology of the top 21 cm of the record was established using ²¹⁰Pb analysis using a constant-rate-of-supply model, and validated with ¹³⁷Cs measurements and the content of spheroidal carbonaceous particles. A tentative chronology for the lower part of the core was obtained through extrapolation of the sedimentation rates in the uppermost part of the record. Pollen assemblages in the record reflect regional changes in forestation and land-use patterns in the Upper Engadine valley and show no evidence of significant local human activity in the lake’s catchment. Diatom assemblages record a distinct increase in planktonic taxa since the early 19th century, suggesting a decrease in the duration of ice-cover. In contrast, chironomid assemblages remained stable during a large part of the record. We applied an established chironomid-based July air temperature transfer function and a newly developed diatom-based spring air temperature transfer function to reconstruct past seasonal air temperature changes at Lej da la Tscheppa. The reconstructions indicate a diatom-inferred warming trend in spring temperatures during the past ca. 400 years, whereas chironomid-inferred summer temperatures suggest a slight cooling trend. These biota-based reconstructions are in good agreement with the centennial-scale temperature trend in an independent reconstruction of regional temperatures in the Upper Engadine region based on instrumental records and documentary proxy evidence from the Alps. Our results suggest that, in high-altitude lakes, independent chironomid- and diatom-based seasonal temperature reconstruction is possible and can be successfully used to track seasonal temperature trends.  相似文献   

Subglacial emplacement of tills and meltwater deposits at the base of overdeepened bedrock troughs          下载免费PDF全文

Marius W. Buechi  Stephan M. Frank  Hans Rudolf Graf  John Menzies  Flavio S. Anselmetti 《Sedimentology》2017,64(3):658-685

The sedimentary infills of subglacially eroded bedrock troughs in the Alps are underexplored archives for the timing, extent and character of Pleistocene glaciations but may contain excellent records of the Quaternary landscape evolution over several glacial–interglacial cycles. The onset of sedimentation in these bedrock troughs is often reflected by diamicts and gravels directly overlying bedrock in the deepest basin segments. Subglacial or proglacial depositional environments have been proposed for these coarse‐grained basal units but their characteristics and origin remain controversial. This article presents results from drill cores that recovered a coarse‐grained basal unit in a major buried bedrock‐trough system in the Lower Glatt Valley, northern Switzerland. The excellent core recovery allowed a detailed study combining macroscopic, microscopic and geochemical methods and gives unprecedented insights into the transition from erosion to deposition in overdeepened bedrock troughs. These results show that the basal infill comprises diamicts, interpreted as subglacial tills, separated by thin sorted interbeds, originating from subglacial cavity deposition. The stacking of these units is interpreted to represent repeated switching between a coupled and decoupled ice–bed‐interface indicating an ever‐transforming mosaic of subglacial bed conditions. Decoupling in response to high basal water pressures is probably promoted by the confined subglacial hydraulic conditions resulting from the bedrock acting as aquitards, the narrow reverse sloping outlet and a large catchment area. While stratigraphic and lithological evidence suggests that erosion and the onset of basal sedimentation occurred during the same glaciation, different scenarios for the relative timing of infilling in relation to formation and glaciation of the bedrock trough are discussed. Overlying deltaic and glaciolacustrine sediments suggest deposition during subsequent deglaciation of the bedrock trough. The basal sediment characteristics are in agreement with previous reports in hydrogeological and seismic exploration and suggest the occurrence of similar basal successions in other subglacially overdeepened basins in the Alps and elsewhere.  相似文献   

季节性放牧对黄河源区高寒草甸植被耗水量及水分利用效率的影响   总被引：1，自引：0，他引：1  

贺慧丹  杨永胜  祝景彬  李红琴  未亚西  李英年 《冰川冻土》2017,39(1):130-139

研究季节性放牧对植被耗水量、水分利用效率的影响,是探索如何提高高寒草甸水源涵养能力的重要内容之一。以青藏高原三江源高寒草甸季节性放牧样地与自然放牧样地为研究对象,分析了季节性放牧和自然放牧条件下高寒草甸植被耗水量、水分盈亏量、水分利用效率（WUE）的动态变化及其与环境因素的关系。结果表明：在植被生长季（5-9月）,季节性放牧样地和自然放牧样地植被耗水量在5月开始增加, 7月达最高,分别为160.94 mm和145.96 mm,季节性放牧样地植被总耗水量（395.52 mm）比自然放牧样地（348.14 mm）高13.61%。生长季平均来看,季节性放牧样地和自然放牧样地5-9月水分正盈余,分别为13.58 mm和70.96 mm,但在植物生长旺季（8月）略有亏缺。季节性放牧样地和自然放牧样地植被耗水量均与降水量呈弱的正相关关系。季节性放牧样地植被地上净初级生产量（ANPP）、地下净初级生产量（BNPP）和总的净初级生产量（NPP）比自然放牧样地分别高32.54 g·m^-2、5.96 g·m^-2、38.50 g·m^-2,季节性放牧样地ANPP的水分利用效率（WUE）比自然放牧样地高53.85%,而BNPP、NPP的WUE比自然放牧样地分别低13.06%和9.97%。这表明,季节性放牧可提高植被生产量和耗水量,但对高寒草甸WUE的影响因放牧方式不同导致地上、地下生物量分配格局不同而有所差异。  相似文献   

两个时期若尔盖高原沼泽湿地景观格局的对比研究   总被引：3，自引：0，他引：3  

陈志科  吕宪国 《湿地科学》2010,8(1):8-14

以若尔盖高原为研究区,选择1977年的Landsat MSS影像、2007年的Landsat TM影像和研究区90m分辨率的数字地形图为数据源,利用景观生态学方法及遥感和地理信息系统技术,对若尔盖高原1977年和2007年两个时期的沼泽湿地(包括沼泽和沼泽化草甸)景观格局进行了对比研究。结果显示,与1977年相比,2007年研究区沼泽与沼泽化草甸的面积比(沼泽面积/沼泽化草甸面积)发生了明显变化,沼泽与沼泽化草甸的面积比由1977年的1/3减少到2007年的1/7;2007年沼泽面积明显减少,其面积只占沼泽湿地总面积的13%;两个时期,研究区沼泽湿地景观都集中连片分布,聚集度均高于90;与1977年相比,2007年沼泽湿地景观的斑块数减少,景观类型趋于单一,而平均斑块面积和聚集度都在增加;研究区沼泽湿地90%以上分布在坡度小于5°的空间范围内,随着坡度的增大,沼泽湿地的退化程度显著增高;与1977年相比,2007年研究区沼泽湿地景观分布质心发生了一定的空间位移,沼泽质心向西南偏移了3.88km,沼泽化草甸质心向东北偏移了12.35km。  相似文献   

Confirming geomorphological interpretations based on portable OSL reader data          下载免费PDF全文

Eric W. Portenga  Paul Bishop 《地球表面变化过程与地形》2016,41(3):427-432

Portable optically stimulated luminescence (OSL) readers are increasingly being used in geomorphological and archaeological investigations, but information regarding data reproducibility and the reliability of interpretations based on portable OSL reader data has not yet been presented to the wider geomorphological community. This Letter addresses these two issues by returning to Grabben Gullen Creek in the southeastern Australian Tablelands where we remeasure a sediment profile that was first measured by other researchers 3 years earlier. We also compare portable OSL reader data measured on sediment interpreted to have been deposited in swampy meadow wetlands and flood alluvium settings with data measured on known swampy meadow and flood deposits. Our data show that portable OSL reader data are reproducible. Moreover, we confirm the earlier interpretation that stratigraphies commonly exposed in southeastern Australian Tablelands valley bottoms reflect pre‐European swampy meadow wetlands and flood alluvium. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

环境因子影响下疏勒河上游高寒草甸物种丰富度与生物量间的关系     

王增如  王成  董晓红  高丙民 《冰川冻土》2016,38(6):1710-1717

生物多样性与生产力的关系是生态学领域争论不休的重要科学问题。调查了青藏高原疏勒河上游高寒草甸典型植物群落物种丰富度、生物量及环境因子,分析了不同植物群落物种丰富度与生物量的关系及其差异性,并探讨了影响两者间关系的关键环境因子。结果表明：1）以莎草科或毛茛科物种为主要建群种的植物群落物种丰富度与生物量不存在显著的相关性（P>0.05）,如高山嵩草+苔草群落、线叶嵩草+黑褐苔草群落、唐松草+矮火绒群落、草苔草+昆仑蒿群落;而以禾本科为建群种的植物群落（紫花针茅+紫菀群落、紫花针茅+沙生风毛菊群落）两者间存着显著正相关性（P<0.05）.2）CCA排序中,环境因子对植物群落分布格局的累计解释量为83.4%,这说明环境异质性是影响植物群落空间格局的主要原因,其中冻土上限埋深是影响植物群落特征及分布的关键环境因子。冻土上限埋深小于-4m时,丰富度与生物量间存在着显著的正相关;冻土上限埋深大于-4m时,两者间无显著相关性。这有助于深刻认识生物多样性与高寒草甸生态系统功能的关系。  相似文献   

祁连山中部亚高山草地作物系数估算   总被引：1，自引：1，他引：0  

高云飞  赵传燕  王清涛  葛红元  王红义  林梅 《中国沙漠》2016,36(5):1419-1425

利用Lysimeter蒸散仪于2011-2014年对祁连山中部黑河上游天涝池流域亚高山草地实际蒸散量进行观测。用FAO Penman-Monteith模型对草地参考蒸散量进行估算,根据草地植被高度结合气象数据,以估算日尺度作物系数,以估算的作物系数与模拟的参考蒸散量计算草地实际蒸散量,并用观测值进行验证。结果表明：FAO改进后的作物系数计算方法适合该区域草地作物系数的计算;以FAO Penman-Monteith模型估算的日蒸散量为0.50~7.26 mm,生长季日均蒸散量有年际变化,2011年 > 2014年 > 2012年 > 2013年。总体来看,土壤蒸发总量年际变化不大,影响蒸散量年际变化的主要部分是植被的蒸腾。  相似文献   

贵州龙里高山草原泥炭沉积年代、速率及其有机碳同位素记录     

文雪峰  魏晓  杨瑞东  田明中 《现代地质》2012,26(4):712-715

通过对贵州龙里高山草原泥炭进行加速器(AMS)14C测年和有机碳的测定,获得泥炭层底部0.90 m和0.55 m处年龄分别为(7 933±33)a B.P.和(7 733±28)a B.P.,计算出泥炭层堆积速率为1.75 mm/a。获得泥炭层δ13C为-28.9‰～-26.6‰,平均为-27.8‰,说明植被以C3植物为主,与现在坪台沼泽上苔藓繁盛相似。结合其他地区的气候记录推断,研究区泥炭发育于相对温暖湿润的气候环境,是全新世大暖期的第一个暖湿期形成的产物。  相似文献   

高山气候对自动气象站运行的影响分析     

王会兵  祁生秀  王小勇  郑自君  郑丽英 《四川气象》2011,(3):65-68

本文对地处我国南方高山的峨眉山自动气象站自2002年10月运行8年来出现或遇到的各种因雷暴、雨雾凇冻结、连续高湿等天气引起的问题进行分析,提出保证高山自动气象站正常运行的一些方法和思路。  相似文献   

青藏高原东坡高原草甸近地层气象要素与能量输送季节变化分析   总被引：1，自引：0，他引：1  

赵兴炳  李跃清 《四川气象》2011,(2):12-17

本文简要介绍了青藏高原东坡理塘大气综合观测站的情况。利用该站2007~2008年观测资料,分析比较了青藏高原东坡地区高原草甸下垫面情况下近地层气象要素及能量输送的季节变化特征。结果表明：理塘地区近地层气象要素及能量输送的季节变化显著,具有明显的水热同期特点。各个季节近地层气象要素和湍流通量,如风、气温、感热通量、潜热通量等,日变化显著。风速、动量通量、摩擦速度等要素的平均日最大值和最小值分别出现在下午和日出前。比湿的峰值出现在日出前。辐射和热平衡分量的日均最大值与最小值分别出现在正午及日出前。地表热源强度分析表明,理塘白天为热源,在春夏秋三季夜间为弱的热源与冷源交替出现。在雨季,潜热输送在陆气间热量交换过程中占主导作用,感热输送是次要的;干季的结果与雨季相反,感热是首要的。  相似文献