In lacustrine sediments,aragonite is a widespread mineral,whereas monohydrocalcite is a rare carbonate mineral. In the cold and high-attitude Xizang (Tibetan) Plateau,where aragonite has been commonly found in lacustr...In lacustrine sediments,aragonite is a widespread mineral,whereas monohydrocalcite is a rare carbonate mineral. In the cold and high-attitude Xizang (Tibetan) Plateau,where aragonite has been commonly found in lacustrine sediments,there is no aragonite,but low-Mg calcite,monohydrocalcite and trace dolomite. The lake receives solutes primarily from surface runoffs and remains fairly constant water chemistry for a long time. The total CaCO3 percentage in sediments could be controlled by evaporation and inflow of detrital materials. The absence of aragonite is unusual when compared to other lacustrine sediments from the Tibetan Plateau. This could be due to low Ca/Mg ratio,low salinity,low Mg and Ca concentration. Monohydrocalcite might precipitate from the lake water mediated by biological activities. Low-Mg calcite originated from minor ostracoda shell and the precipitation of lake water with biological activities.展开更多
Otoliths are biogenic carbonate minerals whose microstructure and microchemistry have been used for age determination, stock identification, life history and environmental tracing. Using X-ray diffraction （XRD） and ...Otoliths are biogenic carbonate minerals whose microstructure and microchemistry have been used for age determination, stock identification, life history and environmental tracing. Using X-ray diffraction （XRD） and Fourier transform infrared （FTIR） spectroscopy, we have determined the mineral types and crystalline characteristics of three pairs of otoliths from naked carp Gymnocypris przewalskii, the predominant fish in Lake Qinghai. The results indicate that the mineral of both lapillus and sagitta of the naked carp is aragonite, and that of asteriscus is vaterite. The aragonite of lapillus has prefect crystallization. Given the shape of lapillus and the sensitivity of its aragonite to water chemistry, lapillus was used to analyze temporal Sr/Ca ratios along the maximal growth axis by an electron probe microanalyzer （EPMA）. Consistent variations of Sr/Ca ratios with a range of 1.0x10-3-5.0~10-3 on the long and short radii indicate that Sr/Ca ratios of lapillus potentially respond to the chemical compositions of the host waters during the period of the naked carp＇s growth and migration. Discontinuous （dark） zones of lapillus were formed during fall and winter when the naked carp grows slowly in Lake Qinghai, resulting in similar low Sr/Ca ratios to lake water, whereas incremental zones with higher St/Ca ratios respond to its migratory river waters during spring and summer. Various Sr/Ca ratios of incremental zones suggest that the migratory pattern of the naked carp may be much more flexible, rather than in a single river. Therefore, high-resolution otolith microchemistry of the naked carp can be used to trace its migratory behavior, which is of significance for determining its migratory pattern and life history of this precious species inhabiting the Tibetan Plateau.展开更多
基金supported by the National Basic Research Program of China (2005CB422000)the National Natural Science Foundation of China (40801075, 40830743, 40701194, 40671023, and 40730101)
文摘In lacustrine sediments,aragonite is a widespread mineral,whereas monohydrocalcite is a rare carbonate mineral. In the cold and high-attitude Xizang (Tibetan) Plateau,where aragonite has been commonly found in lacustrine sediments,there is no aragonite,but low-Mg calcite,monohydrocalcite and trace dolomite. The lake receives solutes primarily from surface runoffs and remains fairly constant water chemistry for a long time. The total CaCO3 percentage in sediments could be controlled by evaporation and inflow of detrital materials. The absence of aragonite is unusual when compared to other lacustrine sediments from the Tibetan Plateau. This could be due to low Ca/Mg ratio,low salinity,low Mg and Ca concentration. Monohydrocalcite might precipitate from the lake water mediated by biological activities. Low-Mg calcite originated from minor ostracoda shell and the precipitation of lake water with biological activities.
基金supported by National Basic Research Program of China (Grant No. 2010CB833400)National Natural Science Foundation of China (Grant No. 40873082)
文摘Otoliths are biogenic carbonate minerals whose microstructure and microchemistry have been used for age determination, stock identification, life history and environmental tracing. Using X-ray diffraction （XRD） and Fourier transform infrared （FTIR） spectroscopy, we have determined the mineral types and crystalline characteristics of three pairs of otoliths from naked carp Gymnocypris przewalskii, the predominant fish in Lake Qinghai. The results indicate that the mineral of both lapillus and sagitta of the naked carp is aragonite, and that of asteriscus is vaterite. The aragonite of lapillus has prefect crystallization. Given the shape of lapillus and the sensitivity of its aragonite to water chemistry, lapillus was used to analyze temporal Sr/Ca ratios along the maximal growth axis by an electron probe microanalyzer （EPMA）. Consistent variations of Sr/Ca ratios with a range of 1.0x10-3-5.0~10-3 on the long and short radii indicate that Sr/Ca ratios of lapillus potentially respond to the chemical compositions of the host waters during the period of the naked carp＇s growth and migration. Discontinuous （dark） zones of lapillus were formed during fall and winter when the naked carp grows slowly in Lake Qinghai, resulting in similar low Sr/Ca ratios to lake water, whereas incremental zones with higher St/Ca ratios respond to its migratory river waters during spring and summer. Various Sr/Ca ratios of incremental zones suggest that the migratory pattern of the naked carp may be much more flexible, rather than in a single river. Therefore, high-resolution otolith microchemistry of the naked carp can be used to trace its migratory behavior, which is of significance for determining its migratory pattern and life history of this precious species inhabiting the Tibetan Plateau.
