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991.
Development of diatom-based salinity models for paleoclimatic research from lakes in British Columbia (Canada) 总被引:2,自引:2,他引:0
Diatoms were identified and enumerated from the surface sediments of 65 lakes located on the Cariboo and Chilcotin Plateaux (British Columbia, Canada). These lakes span a large gradient in lakewater ionic concentration (fresh through hypersaline) and composition, as well as other physical/chemical variables. Almost all of the study lakes had higher salinities in the late-summer than in the spring. The lakes with spring salinities >8 g l–1 showed the largest seasonal increases in salinity. Ionic composition was similar in the spring and late-summer for most lakes. Both ionic concentration (i.e. salinity) and composition were important environmental variables that could account for the different diatom floras in the lakes. Diatom assemblages characteristic of carbonate-dominated and sulfate-dominated waters were identified. Other variables such as water depth and phosphorus concentration were also important.The majority (87%) of diatom taxa had estimated salinity optima < 3 g l–1 Halophilic diatom taxa had broader tolerances to salinity when compared to the fresh water taxa, however taxa with narrow and broad tolerances could be identified across the salinity gradient. Species diversity was weakly but significantly correlated to lakewater salinity (r
2 = 0.18 to 0.3, P < 0.05).Salinity inference models were developed based on the relationship between the diatom assemblages and the spring, late-summer and average salinity. The correlations between the measured and diatominferred salinity, based on the spring (r = 0.95), late-summer (r = 0.94) and average (r = 0.95) salinity data, are high because there was an extremely strong correlation (r = 0.98) between the log transformed spring and late-summer measured salinities. These salinity reconstruction models provide a tool that can be used to infer past climatic changes as part of paleolimnological studies from appropriate closed-basin lakes in British Columbia. 相似文献
992.
Depositing ages of sediment in core CK6 of Qarhan Salt Lake were determined by usingmethods of ~(14)C, ~(230)Th and paleo-terrestrial-magnetism. Based on synthetic analyses for thevariation of the content of organic carbon, sporo-pollen composition and lithofacies, the fluc-tuating model of paleo-climate since 750 ka B.P. was set up. It is divided into 21 fluctua-ting epochs of climate, among them, 11 are warm and humid epochs, and 10 are dry andcold epochs. 相似文献
993.
广西百色第三纪哺乳动物群与气候变迁 总被引:3,自引:3,他引:0
在广西百色共发现了三个层位:晚始新世早期的洞均组,晚始新世晚期的那读组和早渐新世的公康组。它们的哺乳动物的种类数目分别为14,27和ll,而其南方类型的百分含量则分别为50,77.8和54.5。故在晚始新世早期或早渐新世,气候较凉;而在晚始新世晚期,气候较暖。这是与北美的情况相类似的。 相似文献
994.
Anne-Marie Aucour Raymonde Bonnefille Claude Hillaire-Marcel 《Palaeogeography, Palaeoclimatology, Palaeoecology》1999,150(3-4):179-189
The relationship between organic carbon accumulation rates and 13C/12C ratios of total organic carbon (TOC) was investigated in an highland peat bog core (Ru-3) from Equatorial Africa. This core yielded a sequence spanning the last 14 kyr and was analysed with a 100–300 yr resolution for TOC-δ13C values. The Holocene section shows contrasted TOC accumulation regimes and TOC δ13C varying between −28.5 and −19.5‰ with a few very short ‘isotopic excursions' (dated at ca. 9.3, 7.5, 4.2 ka B.P.). The organic carbon accumulation rates range from 2 to 20 mg C cm−2 yr−1. They increase when TOC becomes more depleted in 13C, notably between 12 and 9.8 ka B.P., 8.5 and 7.8 ka B.P. and after 1.6 ka B.P. Periods of restricted carbon storage correspond to heavier TOC accumulation at 9.3, and between 7.5 and 1.6 ka B.P. At the study site, the δ-variations can be related to variable C4-plant inputs, and possibly, to changes in the fractionation between CO2 and the organic carbon in C3 vascular plants. The Ru-3 record indicates restricted carbon storage during the periods of increased contribution from C4 plants and/or of decreased fractionation between CO2 and organic carbon in C3 plants. Changes in TOC-δ13C values in core Ru-3 seem to match fluctuations of East Equatorial African lakes. High lake stands correspond to low δ13C intervals and vice versa. This points to indirect climatic forcing of δ13C changes in intertropical peats. 相似文献
995.
996.
Fan Yu-Chao Qi Yong-An Dai Ming-Yue Qing Guo-Shuai Liu Bing-Chen Bai Wan-Bei 《古地理学报》1999,22(2):367-376
The complete early Cambrian Zhushadong Formation is developed in Dengfeng area,Henan Province,which record important information of paleoclimate variation. The lithology,element geochemistry,sedimentology and palaeontology are investigated to have a closer insight into the paleoclimate and environmental variations during deposition of the early Cambrian Zhushadong Formation of the western Henan. The results show that the Zhushadong Formation can be divided into three lithological members: Lower laminated dolomite Member,the upper leopard limestone Member and the top laminated dolomite Member. The paleoclimate variations are reflected by stratified dissolved pores,chert and gypsum in the laminated dolomites,intensive bioturbation in leopard limestones and multiple geochemical parameters,including Mn concentration,and the ratios of Sr/Cu,Rb/Sr and MgO/CaO. It displays a clear change from hot and arid climate of the lower laminated dolomite Member,to warm and humid climate of the upper leopard limestone Member,and back to hot and arid climate of the top laminated dolomite Member. The contemporaneous sediments in North China show the similar paleoclimate variations to the Zhushadong Formation in western Henan Province. 相似文献
997.
The Pleistocene vermicular red earth in South China signaling the global climatic change: The molecular fossil record 总被引:11,自引:3,他引:8
The widespread (with a distribution area of 2.2?06 km2) Pleistocene red earth is believed to be one of the most detailed records of the environmental and climatic changes in South China. However, the previous research mainly covers the rough dating, pedo… 相似文献
998.
Palynological records of environmental changes in the middle part of Inner Mongolia,China 总被引:8,自引:0,他引:8
SHI Peijun & SONG Changqing . Key Laboratory of Environmental Change Natural Disaster Ministry of Education of China Beijing Normal University Bejing China . National Natural Science Foundation of China Beijing China Correspondence should be addressed to Song Changqing 《科学通报(英文版)》2003,48(14):1433-1438
Today, the central part of Inner Mongolia has a continental climate, with cold winters, hot summers, and approximately 70% of the precipitation falling in the summer months. Vegetation is dominated by steppe vegetation with Stipa bungeana and Stipa breviflora. Scattered individuals of Quercus liaotungensis, Populus davidiana, Betula platyplylla are distributed in the mountains, with some Pinus tabluaoformis, near Miaoyu, and with fragmentary Picea above 1700—1800 m a.s.l. The Huitenglian… 相似文献
999.
Distributions of fatty acids in a stalagmite related to paleoclimate change at Qingjiang in Hubei,southern China 总被引:5,自引:0,他引:5
XIE Shucheng HUANG Junhua WANG Hongmei YI Yi HU Chaoyong CAI Yanjun & CHENG Hai . Faculty of Earth Science China University of Geosciences Wuhan China . School of Environmental Studies China University of Geosciences Wuhan China . SKLLQG Institute of Earth Environment Chinese Academy of Sciences Xi’an China . Department of Geology Geophysics University of Minnesota MN USA 《中国科学D辑(英文版)》2005,48(9):1463-1469
~~Distributions of fatty acids in a stalagmite related to paleoclimate change at Qingjiang in Hubei,southern China1. Dorale, J. A., Edward, R. L., Ito, E. et al., Climate and vegetation history of mid-continent from 75 to 25 ka: A speleothem record from Crevice Cave, Missouri, USA, Science, 1998, 282(5395): 1871-1874.
2. Li, B., Yuan, D., Qin, J. et al., Oxygen and carbon isotopic char- acteristics of rainwater, drip water and present speleofhems in a cave in Guilin area, and thei… 相似文献
1000.