Using gas chromatography-mass spectrometry (GC-MS) technique, a series of biomarkers were identi- fied, including n-alkanes, n-alkane-2-ones, isoprenoid etc. from the loess-paleosol samples collected from the S4 and a...Using gas chromatography-mass spectrometry (GC-MS) technique, a series of biomarkers were identi- fied, including n-alkanes, n-alkane-2-ones, isoprenoid etc. from the loess-paleosol samples collected from the S4 and adjacent L5, L4 of the Luochuan loess section, Northwestern China. Based on these data, especially n-alkanes and high-resolution magnetic susceptibility and grain size data, the pa- leoenvironment and paleovegetation history during S4 was reconstructed. The CPI (Carbon Predomi- nance Index) and correlation between n-alkanes and magnetic susceptibility and grain size data dem- onstrated that the molecular fossils in paleosol and loess layers can reflect the vegetation condition during the loess-paleosol formation, if the allochthonous organic inputs could be excluded reasonably. The ACL (average chain length) index is correlated well with paleomagnetic susceptibility and grain size variations, displaying their good synchrony with warm and humid climate. However, it relatively lagged behind the paleomagnetic susceptibility and the grain size variations when the climate began to deteriorate. During the formation period of paleosol, the n-alkanes was dominated by C31 homologue, indicating that the primary organic input originated from herbs. Our study also demonstrated that the herbs were more flourish than wood plants in Loess Plateau, especially in the Luochuan area during the warm and humid phase, and there was no typical forest vegetation developed in the studied period.展开更多
The selection of high-resolution loess sections is needed in order to determine the climatic variability of the East Asian Monsoon during the last interglacial. Two sequences of S1 on the eastern and west-ern sides of...The selection of high-resolution loess sections is needed in order to determine the climatic variability of the East Asian Monsoon during the last interglacial. Two sequences of S1 on the eastern and west-ern sides of the Liupan Mountain were both composed of five paleosol layers and four loess layers,indicating that there were five strong summer monsoon events and four strong winter monsoon events in MIS5. This corresponds with other records of the East Asian Monsoon,along with NGRIP and the North Atlantic records,implying that the climate of the Northern Hemisphere was very instable during the last interglacial. Two layers of paleosols and one layer of loess had developed during MIS5a and MIS5c. Compared with MIS5e,the climate in MIS5a and MIS5c fluctuated more intensively on a millen-nial scale,whereas the climate was relatively stable in MIS5e.展开更多
We studied the records of elemental carbon (EC) of the last 21 ka in the Weinan loess section, Shanxi Province. The variations of EC abundance and δ13CEC value along with depth (or age) were presented. There are four...We studied the records of elemental carbon (EC) of the last 21 ka in the Weinan loess section, Shanxi Province. The variations of EC abundance and δ13CEC value along with depth (or age) were presented. There are four large peaks of EC abundance around the following years: 20.16 ka, 17.76 ka, 11.97 ka and 4.49 ka. Climatic situation was changed rapidly during these periods. The peaks around 11.97 ka and 20.16 ka are particularly sharp, occurring over intervals of tens to hundreds of years, which could represent short-duration intense events. δ13CEc values in the upper 4 m of the Weinan loess section vary between -11.71‰ and -21.34‰, which suggests that the vegetation pattern of the last 21 ka on the Loess Plateau is G4-dominated grasses.展开更多
Magnetotactic bacteria (MB) have been isolated from 61 samples which have been collected from S0, L1, S1 and L2 layers in the Duanjiapo loess section. A few MB (<25 cell counts per sieve mesh) have been found in lo...Magnetotactic bacteria (MB) have been isolated from 61 samples which have been collected from S0, L1, S1 and L2 layers in the Duanjiapo loess section. A few MB (<25 cell counts per sieve mesh) have been found in loess layers (L1, L2), bow-shaped, each cell containing only two magnetosomes. while much more MB (>125 cells counts per sieve mesh) have been found from paleosol layers (S0, S1), rod-shaped, each cell containing 8-26 magnetosomes arranged in irregular chains. Magnetosomes with Fe and Co as the main metallic elements are spheroid-shaped, and mainly round in cross-section. Normal saturated fatty acids in MB ranged from C14 to C28; almost no monounsaturated fatty acids have been identified. Most suitable oxygen content for MB growing is 10%, and low concentration of organic salt (0.02mmol/L qumsic iron) is beneficial to the forming of magnetosomes. Results suggest that the paleosol development stage is suitable for the growing of MB and the climate fluctuation periods for magnetosomes formation.展开更多
The study on the polarity transition is a hot point subject in current geophysical researches. One of its principal aspects is to observe the variations in direction and intensity of the geomagnetic field during a pol...The study on the polarity transition is a hot point subject in current geophysical researches. One of its principal aspects is to observe the variations in direction and intensity of the geomagnetic field during a polarity transition recorded in various sediments. The展开更多
Weinan section consists of Holocene soil SO, last glacial loess L1, and last interglacial soil S1, furtherly L1 can be subdivided into three layers of loess (L1-1, L1-3, and L1-5), and two layerS of weakly developed s...Weinan section consists of Holocene soil SO, last glacial loess L1, and last interglacial soil S1, furtherly L1 can be subdivided into three layers of loess (L1-1, L1-3, and L1-5), and two layerS of weakly developed soil (L1-2 and L1-4). Based on studying the content variations of Carbonate, free Fe2O3, and the total organic content in Weinan section, the environmental evolution of this region has been discussed over the last glacial-interglacial cycle. Our results indicate that the chemical parameters can be ed as climatic proxy data, and the variations of these indexes reflect the cyclic nature of the Quaternary climatic change. In addition, the climatic records of Weinan section can also be correlated with that of the marine oxygen isotope records, so the environmental evolution of the Loess Plateau is also consistent with the global climatic changes. The unexpected finding is that the climatic curve of L1-5, which can be correlated with stage 4 of marine oxygen isotope records, consists of three troughs and two sandwiched peaks, and may suggest the existence of the second-order warmcold oscillations of this period.展开更多
Two hundred and thirty-five samples collected from Weinan loess section (L2 - S0)have analyzed by TOC (total organic carbon) and pyrolysis hydrocarbons. The curve of TOC with depth has ho set up and compared well with...Two hundred and thirty-five samples collected from Weinan loess section (L2 - S0)have analyzed by TOC (total organic carbon) and pyrolysis hydrocarbons. The curve of TOC with depth has ho set up and compared well with other climatic markers. The main periods of TOC variation of the last 0. 14 Ma are 67.08 ka and 18.29 ka, which is near with the periods of the variation of sunshine, showing that the TOC variation may be controlled by the variation of 65°N sunshine. The distribution of pyrolysis hydrocarbon and its parameters shows that there are two kinds of hydrocarbon associated with climatic change. One is called hydrocarbon pyrolysted directly from organism (pHC2-1) which is in the range of Tmax350℃ - 500℃, and associated with atmospheric water. The other is called carbonate inclusion inclusion (pHC2-2) which is in the range of Tmax 500℃ - 600℃ and formed by evaporation and associated with dry climate. The formula calculating humidity has been deduced Og = pHC2-1/(pHC2-1 + pHC2-2). The range of humidity of the section is 47% - 77% and the reducing is S1-3, S1-2, S0, S1-1, S1-4, S1-2, L1-1, L1-3, and L1-5. And the trend of the humidity is still increasing today.展开更多
We evaluate the applicability of an optical transmission measurement method commonly used for the analysis of the Black Carbon (BC) content of aerosol sample, to determine the BC content of loess sediments. A number o...We evaluate the applicability of an optical transmission measurement method commonly used for the analysis of the Black Carbon (BC) content of aerosol sample, to determine the BC content of loess sediments. A number of different sample pretreatment procedures are developed and compared, leading to an optimum preparation process. The results include: 1) Subtraction of the optical attenuation values before and after heating of the sample filters (“ΔATN”) varies linearly with the sample mass. The slope of the regression line provides the best determination of BC concentration. 2) When the sample mass is small, (NaPO3)6 pretreatment is best for BC measurement, and the BC concentration results are given by the slope of the regression between ΔATN and sample mass, for a series of samples of varying mass. 3) HF pretreatment accompanied by centrifugation and rinsing may produce a negative bias on the result. 4) Replicate measurements of BC for loess samples showed a maximum deviation less than 5.6%, suggesting that measurements of the BC concentration of a sequence of loess samples could determine variations to this degree of significance. 5) The overall trends of BC concentration in loess section sequences were similar for all chemical pretreatments. The BC concentration result for replicate samples is comparable when pretreated by the same procedure.展开更多
基金the Hundred Talent Project of Chinese Academy of Sciences and the National Natural Science Foundation of China (Grant No. 40371117)
文摘Using gas chromatography-mass spectrometry (GC-MS) technique, a series of biomarkers were identi- fied, including n-alkanes, n-alkane-2-ones, isoprenoid etc. from the loess-paleosol samples collected from the S4 and adjacent L5, L4 of the Luochuan loess section, Northwestern China. Based on these data, especially n-alkanes and high-resolution magnetic susceptibility and grain size data, the pa- leoenvironment and paleovegetation history during S4 was reconstructed. The CPI (Carbon Predomi- nance Index) and correlation between n-alkanes and magnetic susceptibility and grain size data dem- onstrated that the molecular fossils in paleosol and loess layers can reflect the vegetation condition during the loess-paleosol formation, if the allochthonous organic inputs could be excluded reasonably. The ACL (average chain length) index is correlated well with paleomagnetic susceptibility and grain size variations, displaying their good synchrony with warm and humid climate. However, it relatively lagged behind the paleomagnetic susceptibility and the grain size variations when the climate began to deteriorate. During the formation period of paleosol, the n-alkanes was dominated by C31 homologue, indicating that the primary organic input originated from herbs. Our study also demonstrated that the herbs were more flourish than wood plants in Loess Plateau, especially in the Luochuan area during the warm and humid phase, and there was no typical forest vegetation developed in the studied period.
基金Supported by the "973" Project (Grant No. 2005CB422001)the National Natural Science Foundation of China (Grant Nos. 40471016 and 40401007)the Doctoral Foundation of Ministry of Education, China (Grant No. 20030730017).
文摘The selection of high-resolution loess sections is needed in order to determine the climatic variability of the East Asian Monsoon during the last interglacial. Two sequences of S1 on the eastern and west-ern sides of the Liupan Mountain were both composed of five paleosol layers and four loess layers,indicating that there were five strong summer monsoon events and four strong winter monsoon events in MIS5. This corresponds with other records of the East Asian Monsoon,along with NGRIP and the North Atlantic records,implying that the climate of the Northern Hemisphere was very instable during the last interglacial. Two layers of paleosols and one layer of loess had developed during MIS5a and MIS5c. Compared with MIS5e,the climate in MIS5a and MIS5c fluctuated more intensively on a millen-nial scale,whereas the climate was relatively stable in MIS5e.
基金This work was supported by the National Natural Science Foundation of China (Grant No. 49773186) the National Key Basic Research Project (Grant No. G1999043401) the Natural Resources and Environment Program, the CAS (Grant Nos. KZ951-A1-402-08-01 and
文摘We studied the records of elemental carbon (EC) of the last 21 ka in the Weinan loess section, Shanxi Province. The variations of EC abundance and δ13CEC value along with depth (or age) were presented. There are four large peaks of EC abundance around the following years: 20.16 ka, 17.76 ka, 11.97 ka and 4.49 ka. Climatic situation was changed rapidly during these periods. The peaks around 11.97 ka and 20.16 ka are particularly sharp, occurring over intervals of tens to hundreds of years, which could represent short-duration intense events. δ13CEc values in the upper 4 m of the Weinan loess section vary between -11.71‰ and -21.34‰, which suggests that the vegetation pattern of the last 21 ka on the Loess Plateau is G4-dominated grasses.
基金Project supported by the National Natural Science Foundation of China.
文摘Magnetotactic bacteria (MB) have been isolated from 61 samples which have been collected from S0, L1, S1 and L2 layers in the Duanjiapo loess section. A few MB (<25 cell counts per sieve mesh) have been found in loess layers (L1, L2), bow-shaped, each cell containing only two magnetosomes. while much more MB (>125 cells counts per sieve mesh) have been found from paleosol layers (S0, S1), rod-shaped, each cell containing 8-26 magnetosomes arranged in irregular chains. Magnetosomes with Fe and Co as the main metallic elements are spheroid-shaped, and mainly round in cross-section. Normal saturated fatty acids in MB ranged from C14 to C28; almost no monounsaturated fatty acids have been identified. Most suitable oxygen content for MB growing is 10%, and low concentration of organic salt (0.02mmol/L qumsic iron) is beneficial to the forming of magnetosomes. Results suggest that the paleosol development stage is suitable for the growing of MB and the climate fluctuation periods for magnetosomes formation.
文摘The study on the polarity transition is a hot point subject in current geophysical researches. One of its principal aspects is to observe the variations in direction and intensity of the geomagnetic field during a polarity transition recorded in various sediments. The
文摘Weinan section consists of Holocene soil SO, last glacial loess L1, and last interglacial soil S1, furtherly L1 can be subdivided into three layers of loess (L1-1, L1-3, and L1-5), and two layerS of weakly developed soil (L1-2 and L1-4). Based on studying the content variations of Carbonate, free Fe2O3, and the total organic content in Weinan section, the environmental evolution of this region has been discussed over the last glacial-interglacial cycle. Our results indicate that the chemical parameters can be ed as climatic proxy data, and the variations of these indexes reflect the cyclic nature of the Quaternary climatic change. In addition, the climatic records of Weinan section can also be correlated with that of the marine oxygen isotope records, so the environmental evolution of the Loess Plateau is also consistent with the global climatic changes. The unexpected finding is that the climatic curve of L1-5, which can be correlated with stage 4 of marine oxygen isotope records, consists of three troughs and two sandwiched peaks, and may suggest the existence of the second-order warmcold oscillations of this period.
文摘Two hundred and thirty-five samples collected from Weinan loess section (L2 - S0)have analyzed by TOC (total organic carbon) and pyrolysis hydrocarbons. The curve of TOC with depth has ho set up and compared well with other climatic markers. The main periods of TOC variation of the last 0. 14 Ma are 67.08 ka and 18.29 ka, which is near with the periods of the variation of sunshine, showing that the TOC variation may be controlled by the variation of 65°N sunshine. The distribution of pyrolysis hydrocarbon and its parameters shows that there are two kinds of hydrocarbon associated with climatic change. One is called hydrocarbon pyrolysted directly from organism (pHC2-1) which is in the range of Tmax350℃ - 500℃, and associated with atmospheric water. The other is called carbonate inclusion inclusion (pHC2-2) which is in the range of Tmax 500℃ - 600℃ and formed by evaporation and associated with dry climate. The formula calculating humidity has been deduced Og = pHC2-1/(pHC2-1 + pHC2-2). The range of humidity of the section is 47% - 77% and the reducing is S1-3, S1-2, S0, S1-1, S1-4, S1-2, L1-1, L1-3, and L1-5. And the trend of the humidity is still increasing today.
文摘We evaluate the applicability of an optical transmission measurement method commonly used for the analysis of the Black Carbon (BC) content of aerosol sample, to determine the BC content of loess sediments. A number of different sample pretreatment procedures are developed and compared, leading to an optimum preparation process. The results include: 1) Subtraction of the optical attenuation values before and after heating of the sample filters (“ΔATN”) varies linearly with the sample mass. The slope of the regression line provides the best determination of BC concentration. 2) When the sample mass is small, (NaPO3)6 pretreatment is best for BC measurement, and the BC concentration results are given by the slope of the regression between ΔATN and sample mass, for a series of samples of varying mass. 3) HF pretreatment accompanied by centrifugation and rinsing may produce a negative bias on the result. 4) Replicate measurements of BC for loess samples showed a maximum deviation less than 5.6%, suggesting that measurements of the BC concentration of a sequence of loess samples could determine variations to this degree of significance. 5) The overall trends of BC concentration in loess section sequences were similar for all chemical pretreatments. The BC concentration result for replicate samples is comparable when pretreated by the same procedure.
