The chemistry of major cations （Mg^2＋, Ca^2＋, Na^＋, and K^＋） and anions （HCO3^-, SO4^2-, and CI^-） in the water of Lake Pumayum Co and its inflow river was studied, revealing the obvious ionic difference among...The chemistry of major cations （Mg^2＋, Ca^2＋, Na^＋, and K^＋） and anions （HCO3^-, SO4^2-, and CI^-） in the water of Lake Pumayum Co and its inflow river was studied, revealing the obvious ionic difference among various inflow rivers and the lake. The chemical type of the lake water was Mg^2＋-Ca^2＋-HCO3^- -SO^2＋, but the major ions of the main inflow rivers were Ca^2＋-Mg^2＋-HCO3^-. In the lake inlet of Jiaqu River, the main inflow river, there was significant variance of water chemistry within the depth less than 2 m. However, it was almost homogeneous at other area of the lake. Therefore, with the evidence of distribution of water chemistry and oxygen isotope of lake water, a conclusion can be outlined that Jiaqu River had a distinct effect on the hydrochemistry of the water on the submerged delta, whereas this is not the case for other rivers. The Gibbs plot revealed that the dominant mechanism responsible for controlling chemical compositions of the lake water was rocks weathering in the drainage area. Ion ratios and ternary plots further explored the main processes controlling the water chemistry of the catchment, i.e., carbonate weathering, pyrite weathering, and silicate weathering. The different hydrochemistry characteristics between river water and lake water may result from the CaCO3 precipitation. The findings will benefit the explanation of the environmental significance of carbonate in paleolimnological studies in the lake.展开更多
In this study,67 surface sediment samples collected from Nam Co in central Tibet were analyzed for total carbon,total organic carbon and total nitrogen,and 51 of these samples were also analyzed for n-alkanes.The orig...In this study,67 surface sediment samples collected from Nam Co in central Tibet were analyzed for total carbon,total organic carbon and total nitrogen,and 51 of these samples were also analyzed for n-alkanes.The origin and spatial distribution of organic matter were then investigated using these proxies,and the control factors responsible for the spatial distribution patterns and paleolimnological significance were discussed.The results indicated that the origin of organic matter in surface sediment of Nam Co is consistent with the sources of n-alkanes,which were primarily submerged plants,followed by terrestrial plants,and then aquatic algae and bacteria.The organic matter in surface sediments of the lake showed typical spatial variability.Because of the great influence of underwater topography,river inputs and water quality,the spatial distribution of organic matter is enriched from the source to the deposit center.This spatial variability of organic matter in the lake indicates that the sediments in different areas have different sensitivities to environmental changes,which is important to reconstruction of paleoenvironments and paleoclimate using lake sediment cores.展开更多
The n-alkanes are extracted from NMLC-1 core that was drilled in the Nam Co, central Tibet. They are measured by using Gas Chromatography and Mass Spectrometry (GC/MS) for componential and quantitative analyses. Accor...The n-alkanes are extracted from NMLC-1 core that was drilled in the Nam Co, central Tibet. They are measured by using Gas Chromatography and Mass Spectrometry (GC/MS) for componential and quantitative analyses. According to the constructed depth-age model, the component and concentration of n-alkanes, together with total organic carbon (TOC), total nitrogen (TN) and carbonate are used to elu- cidate palaeoenvironmental changes of Nam Co during the past 8.4 ka. The results indicate that Holo- cene environment performs three stages in the lake area. In the stage of 8.4―6.7 kaB.P., it was warmer while precipitation slightly increased. This stage was ended by an obvious cold/dry event. During 6.7― 5.8 kaB.P., temperature increased rapidly and reached its maximum values at about 6.0 kaB.P. The environments were warm/wet optimum for the blooming of terrestrial plants and submerged aquatic plants. After that, temperature decreased continuously and showed the lowest values at about 3.0 kaB.P. From 2.9 kaB.P. to the present, temperature rose again but alternated with cold and warm. The lake area tended to be dry after 1.4 kaB.P. During 600―400 aB.P., the environmental feature was the reflection of "Little Ice Age".展开更多
Under the background of global warming,some lakes on the Tibetan Plateau(TP) are potentially sensitive to temperature change.With a case study of Pumayum Co,where glacier meltwater is important to supply(we call this ...Under the background of global warming,some lakes on the Tibetan Plateau(TP) are potentially sensitive to temperature change.With a case study of Pumayum Co,where glacier meltwater is important to supply(we call this a glacier-fed lake hereafter),we analyze the sensitivity of lake sediment grain size to temperature change.This is done by resolving the modern hydrodynamic process,coupled with comparison of paleoclimatic proxies.According to the spatial distributions of parameters,percentage of grain size and the grain size frequency distribution curve,hydrodynamic processes are analyzed.Five clastic sedimentation types are thereby discriminated.In the open lake area,suspended load transport is the main transport agent.Grain Size Trend Analysis(GSTA),a sediment dynamics model,reveals a trend toward eastward transport.This indicates that the largest and glacier-fed river,the Jiaqu River,influences the entire lake(not just the subsurface alluvial fan),and that lake sediment grain size may serve as a temperature indicator.Time series comparison between grain size of a short core from the central lake and meteorological data confirms this temperature indication,which in turn shows reliability of the method discriminating the hydrodynamic process.This case study will improve the ability of paleoclimatic reconstruction using lake sediment in glacier-fed lakes on the Tibetan Plateau.展开更多
基金Foundation： National Natural Science Foundation of China, No.40871099 National Basic Research Program of China, No.2005CB422002 Knowledge Innovation Project of CAS, No. KZCX2-YW-146-4 Acknowledgment The authors are grateful to Dr. Feng Jinliang and Dr. Zhang Qianggong from Institute of Tibetan Plateau Research, Chinese Academy of Sciences （ITPCAS）, for their helpful discussion during this study, to Ms. Gao Jing from ITPCAS for supplying oxygen isotope data, to Dr. Huang Qiumei from Academy of Mathematics and Systems Science, Chinese Academy of Sciences, for her hard work at English improvement.
文摘The chemistry of major cations （Mg^2＋, Ca^2＋, Na^＋, and K^＋） and anions （HCO3^-, SO4^2-, and CI^-） in the water of Lake Pumayum Co and its inflow river was studied, revealing the obvious ionic difference among various inflow rivers and the lake. The chemical type of the lake water was Mg^2＋-Ca^2＋-HCO3^- -SO^2＋, but the major ions of the main inflow rivers were Ca^2＋-Mg^2＋-HCO3^-. In the lake inlet of Jiaqu River, the main inflow river, there was significant variance of water chemistry within the depth less than 2 m. However, it was almost homogeneous at other area of the lake. Therefore, with the evidence of distribution of water chemistry and oxygen isotope of lake water, a conclusion can be outlined that Jiaqu River had a distinct effect on the hydrochemistry of the water on the submerged delta, whereas this is not the case for other rivers. The Gibbs plot revealed that the dominant mechanism responsible for controlling chemical compositions of the lake water was rocks weathering in the drainage area. Ion ratios and ternary plots further explored the main processes controlling the water chemistry of the catchment, i.e., carbonate weathering, pyrite weathering, and silicate weathering. The different hydrochemistry characteristics between river water and lake water may result from the CaCO3 precipitation. The findings will benefit the explanation of the environmental significance of carbonate in paleolimnological studies in the lake.
基金supported by the National Basic Research Program of China(2012-CB956100)the National Natural Science Foundation of China(41190082, 41071123)the Knowledge Innovation Key Program of the Chinese Academy of Sciences(KZCX2-EW-113)
文摘In this study,67 surface sediment samples collected from Nam Co in central Tibet were analyzed for total carbon,total organic carbon and total nitrogen,and 51 of these samples were also analyzed for n-alkanes.The origin and spatial distribution of organic matter were then investigated using these proxies,and the control factors responsible for the spatial distribution patterns and paleolimnological significance were discussed.The results indicated that the origin of organic matter in surface sediment of Nam Co is consistent with the sources of n-alkanes,which were primarily submerged plants,followed by terrestrial plants,and then aquatic algae and bacteria.The organic matter in surface sediments of the lake showed typical spatial variability.Because of the great influence of underwater topography,river inputs and water quality,the spatial distribution of organic matter is enriched from the source to the deposit center.This spatial variability of organic matter in the lake indicates that the sediments in different areas have different sensitivities to environmental changes,which is important to reconstruction of paleoenvironments and paleoclimate using lake sediment cores.
基金Supported by the National Basic Research Program of China (Grant No. 2005CB422002)the National Natural Science Foundation of China (Grant Nos. 40571172 and 40331006)EU Sixth Framework Projects (BRAHMATWINN, Grant No. FP6-036952)
文摘The n-alkanes are extracted from NMLC-1 core that was drilled in the Nam Co, central Tibet. They are measured by using Gas Chromatography and Mass Spectrometry (GC/MS) for componential and quantitative analyses. According to the constructed depth-age model, the component and concentration of n-alkanes, together with total organic carbon (TOC), total nitrogen (TN) and carbonate are used to elu- cidate palaeoenvironmental changes of Nam Co during the past 8.4 ka. The results indicate that Holo- cene environment performs three stages in the lake area. In the stage of 8.4―6.7 kaB.P., it was warmer while precipitation slightly increased. This stage was ended by an obvious cold/dry event. During 6.7― 5.8 kaB.P., temperature increased rapidly and reached its maximum values at about 6.0 kaB.P. The environments were warm/wet optimum for the blooming of terrestrial plants and submerged aquatic plants. After that, temperature decreased continuously and showed the lowest values at about 3.0 kaB.P. From 2.9 kaB.P. to the present, temperature rose again but alternated with cold and warm. The lake area tended to be dry after 1.4 kaB.P. During 600―400 aB.P., the environmental feature was the reflection of "Little Ice Age".
基金supported by the National Natural Science Foundation of China(41130529,41101181 and 41102117)the Knowledge Innovation Key Program of the Chinese Academy of Sciences (KZCX2-EW-113 and KZCX2-YW-146)
文摘Under the background of global warming,some lakes on the Tibetan Plateau(TP) are potentially sensitive to temperature change.With a case study of Pumayum Co,where glacier meltwater is important to supply(we call this a glacier-fed lake hereafter),we analyze the sensitivity of lake sediment grain size to temperature change.This is done by resolving the modern hydrodynamic process,coupled with comparison of paleoclimatic proxies.According to the spatial distributions of parameters,percentage of grain size and the grain size frequency distribution curve,hydrodynamic processes are analyzed.Five clastic sedimentation types are thereby discriminated.In the open lake area,suspended load transport is the main transport agent.Grain Size Trend Analysis(GSTA),a sediment dynamics model,reveals a trend toward eastward transport.This indicates that the largest and glacier-fed river,the Jiaqu River,influences the entire lake(not just the subsurface alluvial fan),and that lake sediment grain size may serve as a temperature indicator.Time series comparison between grain size of a short core from the central lake and meteorological data confirms this temperature indication,which in turn shows reliability of the method discriminating the hydrodynamic process.This case study will improve the ability of paleoclimatic reconstruction using lake sediment in glacier-fed lakes on the Tibetan Plateau.
