A series of faulted inland basins were developed in the central Qinghai-Tibet Plateau, among which the Co Ngoin Basin containing thick lacustrine sediments is located in the peripheral area of the Indian monsoon. In t...A series of faulted inland basins were developed in the central Qinghai-Tibet Plateau, among which the Co Ngoin Basin containing thick lacustrine sediments is located in the peripheral area of the Indian monsoon. In this paper, we present the weathering history and paleoclimatic changes in the last 2.8 Ma based on studies of high-resolution temporal distributions of Sr, Rb and Zr concentrations, Rb/Sr and Zr/Rb ratios and δ 13C and TOC for the Co Ngoin sediments, in combination with the sediment properties, grain size distribution and clay mineralogy. The sedimentary records indicate three environmental stages in the last 2.8 Ma. At the core depth of 197?170 m (about 2.8?2.5 Ma), low-intensity chemical weathering in the Co Ngoin catchment was experienced under warm-dry to cool-wet climate conditions with relatively low Sr concentration and high Rb/Sr and Zr/Rb ratios. The sudden occurrence of both subalpine coniferous forest and coarse sand and gravel sediments in the Co Ngoin core reflects a strong tectonic uplift. The high Sr concentrations and low Rb/Sr and Zr/Rb ratios reflect a relatively strong chemical weathering between 2.5 Ma and 0.8 Ma (at the core depth of 170?38.5 m) under a temperate/cool and wet climate, characterized by mud and silt with fine sand, probably indicating a stable process of denudation and planation of the plateau. Above the depth of 38.5 m (about 0.8?0 Ma), the coarsening of sediments indicates a strong tectonic uplift and a relatively low intensity of chemical weathering as supported by the record of sediments having relatively low Sr concentrations and high Rb/Sr and Zr/Rb ratios. Since then, the plateau has taken the shape of the modern topographic pattern above 4000 m a.s.l.展开更多
Simulated research of internal loading and col- lecting and analyzing the samples from the lakes were carried out before and after dredging in polluted suburb lakes, Wuli Lake (Wuxi City) and Xuanwu Lake (Nanjing City...Simulated research of internal loading and col- lecting and analyzing the samples from the lakes were carried out before and after dredging in polluted suburb lakes, Wuli Lake (Wuxi City) and Xuanwu Lake (Nanjing City). The research results showed that dredging can in- hibit internal loadings in a certain degree in a short term. The discrepancy of dredging effect and technical level, namely dredging quality, by different dredging methods will result in a difference of control of lake internal Ioad- ings. The internal Ioadings’ reversion will gradually ap- pear along with the bio-geochemical processes, including suspended particle precipi-tation, hydrodynamic distur- bance and microbio-transfor-mation. The reversion rate mainly depends on the dredging method and the change of interfacial processes on the new-born surface layer. The higher nutrient contents and organic matter in the sedi- ment will enhance water-sediment interfa-cial processes and nutrients regeneration. It is very impor-tant to study the physicochemicai and biological character of lacustrine sediments before dredging for determining the dredging methods and predicting their environmental ef- fect.展开更多
A continuous pollen record from the Zoige Basin in the northeastern Qinghai-Tibetan Plateau not only provides information on the vegetation and climate changes during the last two glacial/interglacial cycles, but also...A continuous pollen record from the Zoige Basin in the northeastern Qinghai-Tibetan Plateau not only provides information on the vegetation and climate changes during the last two glacial/interglacial cycles, but also gives proof to establish the time scale of the upper 60 m of the RM core. Subalpine spruce-fir forests colonized the Zoige Basin during the interglacials and interstadials, implying warm and wet climate conditions. Alpine periglacial desert or dry desert may have existed during the penultimate glacial and the last glacial maxima, respectively. Alpine sedge meadow dominated the landscape during MIS 4. The MIS 3 is punc- tuated by a number of stadials similar to those documented in the Guliya and GISP2 ice cores, as indicated by repeated rise and fall of subalpine spruce-fir forests. Our pollen re- cord reveals a regional climate history similar to those from the neighboring sites, including the Arabian Sea and the Guliya ice core, and thus supports the notion that the Qing- hai-Tibetan Plateau acts as an important link between cli- matic events in the North Atlantic realm and the Asian mon- soon domain.展开更多
The evidence of human activities around Erhai Lake catchment was revealed by pollen records from a sedi- ment core in the lake, northwest Yunnan Province. The 14 chronologic sequence based on AMS C data made it possi-...The evidence of human activities around Erhai Lake catchment was revealed by pollen records from a sedi- ment core in the lake, northwest Yunnan Province. The 14 chronologic sequence based on AMS C data made it possi- ble for pollen results to compare with archaeological records and historical documents. The preliminary deforestation started from the selective clearance at about 5500 C a BP, 14 marked by the loss of vertically distributed montane forest and the expansion of second pine woodland across the catchment. The deforestation resulted in the increase of sur- face runoff and the enhanced erosion in the catchment. The increased herbs of pasture and crop suggested the primitive agriculture and stockbreeding in study region. With the lim- ited human activity, as well as the suitable climatic condition, second pine forest expanded quickly, resulting in the weak- ened soil erosion around the basin. The strong forest clear- ance inferred from pollen occurred since 2160 C a BP, par- 14 alleling to the first dense immigration of population, when Yeyu County was first set up around west coast of Erhai Lake, documented in historic record. The development of agriculture led to the steady enhancement of soil erosion from farming land, increasing the input of fine materials and nutrients to the lake. Moreover, the serious deforestation by human activity stressed the vulnerability in ecosystem of the landscape. The time of primary anthropologic impact re- corded from pollen is earlier than that of the oldest archaeo- logical record by 1500 a (14C year).展开更多
The 87Sr/86Sr ratios of silicate (acid-insoluble, AI) and carbonate (acid-soluble, AS) of the lake sediments from the Daihai Lake, Inner Mongolia, since the last 500 years are measured respectively, indicating that ch...The 87Sr/86Sr ratios of silicate (acid-insoluble, AI) and carbonate (acid-soluble, AS) of the lake sediments from the Daihai Lake, Inner Mongolia, since the last 500 years are measured respectively, indicating that chemical weathering of silicate minerals was in an early stage since the Little Ice Age within the Daihai watershed by combination with mineral constitute, Rb/Sr ratio and CaCO3 content in the sediments. During the Little Ice Age maximum, an evi-dent peak in the 87Sr/86Sr ratios of both silicate and carbon-ate in sediments suggests that a cold climate condition is un-favorable to dissolving radiogenic strontium from silicate minerals. Meanwhile, the variation of 87Sr/86Sr ratios of sili-cate and carbonate also reflects a projected warming climate favorable to intensifying chemical weathering after the Little Ice Age. Consequently, the 87Sr/86Sr ratio of both silicate and carbonate in inland lake sediments can be used as an effec-tive proxy of the past climate in single watershed.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.40373004)the National Key Basic Research Science Foundation(Grant No.G199804O810)+1 种基金the UK Royal Society BP Research Fellowshipthe Doctors Foundation of Liaocheng University.
文摘A series of faulted inland basins were developed in the central Qinghai-Tibet Plateau, among which the Co Ngoin Basin containing thick lacustrine sediments is located in the peripheral area of the Indian monsoon. In this paper, we present the weathering history and paleoclimatic changes in the last 2.8 Ma based on studies of high-resolution temporal distributions of Sr, Rb and Zr concentrations, Rb/Sr and Zr/Rb ratios and δ 13C and TOC for the Co Ngoin sediments, in combination with the sediment properties, grain size distribution and clay mineralogy. The sedimentary records indicate three environmental stages in the last 2.8 Ma. At the core depth of 197?170 m (about 2.8?2.5 Ma), low-intensity chemical weathering in the Co Ngoin catchment was experienced under warm-dry to cool-wet climate conditions with relatively low Sr concentration and high Rb/Sr and Zr/Rb ratios. The sudden occurrence of both subalpine coniferous forest and coarse sand and gravel sediments in the Co Ngoin core reflects a strong tectonic uplift. The high Sr concentrations and low Rb/Sr and Zr/Rb ratios reflect a relatively strong chemical weathering between 2.5 Ma and 0.8 Ma (at the core depth of 170?38.5 m) under a temperate/cool and wet climate, characterized by mud and silt with fine sand, probably indicating a stable process of denudation and planation of the plateau. Above the depth of 38.5 m (about 0.8?0 Ma), the coarsening of sediments indicates a strong tectonic uplift and a relatively low intensity of chemical weathering as supported by the record of sediments having relatively low Sr concentrations and high Rb/Sr and Zr/Rb ratios. Since then, the plateau has taken the shape of the modern topographic pattern above 4000 m a.s.l.
文摘Simulated research of internal loading and col- lecting and analyzing the samples from the lakes were carried out before and after dredging in polluted suburb lakes, Wuli Lake (Wuxi City) and Xuanwu Lake (Nanjing City). The research results showed that dredging can in- hibit internal loadings in a certain degree in a short term. The discrepancy of dredging effect and technical level, namely dredging quality, by different dredging methods will result in a difference of control of lake internal Ioad- ings. The internal Ioadings’ reversion will gradually ap- pear along with the bio-geochemical processes, including suspended particle precipi-tation, hydrodynamic distur- bance and microbio-transfor-mation. The reversion rate mainly depends on the dredging method and the change of interfacial processes on the new-born surface layer. The higher nutrient contents and organic matter in the sedi- ment will enhance water-sediment interfa-cial processes and nutrients regeneration. It is very impor-tant to study the physicochemicai and biological character of lacustrine sediments before dredging for determining the dredging methods and predicting their environmental ef- fect.
基金This work was supported by 973 Project of China(Grant No.998040810)the National Key Project for the Qinghai-Tibetan Plateau in the Eighth Five year Project of China+1 种基金the National Natural Science Foundation of China(Grant Nos.49371068 and 49871078)the U.S.National Science Foundation.
文摘A continuous pollen record from the Zoige Basin in the northeastern Qinghai-Tibetan Plateau not only provides information on the vegetation and climate changes during the last two glacial/interglacial cycles, but also gives proof to establish the time scale of the upper 60 m of the RM core. Subalpine spruce-fir forests colonized the Zoige Basin during the interglacials and interstadials, implying warm and wet climate conditions. Alpine periglacial desert or dry desert may have existed during the penultimate glacial and the last glacial maxima, respectively. Alpine sedge meadow dominated the landscape during MIS 4. The MIS 3 is punc- tuated by a number of stadials similar to those documented in the Guliya and GISP2 ice cores, as indicated by repeated rise and fall of subalpine spruce-fir forests. Our pollen re- cord reveals a regional climate history similar to those from the neighboring sites, including the Arabian Sea and the Guliya ice core, and thus supports the notion that the Qing- hai-Tibetan Plateau acts as an important link between cli- matic events in the North Atlantic realm and the Asian mon- soon domain.
基金supported by the Continent Drilling Project(KZCX2-SW-118)the National Natural Science Foundation of China(Grant No.40331003)Leverhulme(Grant No.F00025/E).
文摘The evidence of human activities around Erhai Lake catchment was revealed by pollen records from a sedi- ment core in the lake, northwest Yunnan Province. The 14 chronologic sequence based on AMS C data made it possi- ble for pollen results to compare with archaeological records and historical documents. The preliminary deforestation started from the selective clearance at about 5500 C a BP, 14 marked by the loss of vertically distributed montane forest and the expansion of second pine woodland across the catchment. The deforestation resulted in the increase of sur- face runoff and the enhanced erosion in the catchment. The increased herbs of pasture and crop suggested the primitive agriculture and stockbreeding in study region. With the lim- ited human activity, as well as the suitable climatic condition, second pine forest expanded quickly, resulting in the weak- ened soil erosion around the basin. The strong forest clear- ance inferred from pollen occurred since 2160 C a BP, par- 14 alleling to the first dense immigration of population, when Yeyu County was first set up around west coast of Erhai Lake, documented in historic record. The development of agriculture led to the steady enhancement of soil erosion from farming land, increasing the input of fine materials and nutrients to the lake. Moreover, the serious deforestation by human activity stressed the vulnerability in ecosystem of the landscape. The time of primary anthropologic impact re- corded from pollen is earlier than that of the oldest archaeo- logical record by 1500 a (14C year).
基金This work was supported by the National Natural Science Foundation of China (Grant No. 40003001) the National Key Basic Research Devel-opment Program (Grant No. G1999043400) and Nanjing Institute of Geography and Limnology Director Foundation (Grant No
文摘The 87Sr/86Sr ratios of silicate (acid-insoluble, AI) and carbonate (acid-soluble, AS) of the lake sediments from the Daihai Lake, Inner Mongolia, since the last 500 years are measured respectively, indicating that chemical weathering of silicate minerals was in an early stage since the Little Ice Age within the Daihai watershed by combination with mineral constitute, Rb/Sr ratio and CaCO3 content in the sediments. During the Little Ice Age maximum, an evi-dent peak in the 87Sr/86Sr ratios of both silicate and carbon-ate in sediments suggests that a cold climate condition is un-favorable to dissolving radiogenic strontium from silicate minerals. Meanwhile, the variation of 87Sr/86Sr ratios of sili-cate and carbonate also reflects a projected warming climate favorable to intensifying chemical weathering after the Little Ice Age. Consequently, the 87Sr/86Sr ratio of both silicate and carbonate in inland lake sediments can be used as an effec-tive proxy of the past climate in single watershed.
