青海湖沉积物中的甾醇及其演化

Ｃ_２７，Ｃ_２８和Ｃ_２９甾醇（△５.２２，△２２，△５和△５.２４（２８）和５α－甾烷醇）在青海湖三孔近代沉积物（ＱＨ，ＱＥ和ＱＯ）中被检出。其中以Ｃ_２９甾醇占优势。在ＱＥ和ＱＧ孔沉积物中还检出了低浓度的三个Ｃ_３０甾醇（４α，２３，２４－三甲基－５α－胆甾－２２Ｅ－烯醇（甲藻甾醇），４α－甲基－２４－乙基－５α－胆甾－２２Ｅ－烯醇和４α－甲基－２４－乙基－５α－胆甾烷醇］。在ＱＨ和ＱＧ孔上部层段沉积物中，Ｃ_２７，Ｃ_２９.饱和的和不饱和的甾醇的碳数分布的平行性，甾烷醇/△５－甾醇及△２２－/△５.２２－甾醇的比值随沉积物埋深而增加提供了甾酸氢化作用的间接证据。青海湖沉积物中的甾醇主要来自湖区丰富的高等植物和湖中的藻类等。在ＱＧ孔８０～１００ｃｍ和１２０～１４０ｃｍ层段沉积物中，５ａ－胆甾烷醇浓度迅速增加可能反映特殊的生物（介形类）对该二层段沉积物中高浓度的胆甾烷醇的贡献。

Sterols and their Evolution of Qinghai Lake Sediments

C₂₇ ,C₂₈, C₂₉sterols, including△5,22,△22,△5and △5,22(28)，and 5a-stanols have been identified in the three recent sediment cores of Qinghai Lake QH core (near Heima River mouth, water depth : 0. 5m，core length:30cm )，QG core ( in Gahai，water depth:9m, core lengths 230cm，water salinity:33‰) and QE core (in Erhai，water depth:4m , core length:30cm, fresh water)].C₂₉ sterols, especially 24-ethylcholesta-5, 22E-then-3β-ol and 24-ethylcholest-5-en-3β-ol, preponderate in all sections of the three sediment cores. Three C₃₀ sterols (4α, 23, 24-trimethy-5α-chelest-22E-en -3β-ol(dinosterol ) , 4α-methy-24-ethyl- 5α-chokest- 22E- 3β-ol and its saturated analog(4α-methyl-24-ethyl-5α-chelestan-3β-ol) are also detected at low concentrations in the QE and QG sediment cores of the lake. The parallelism between the C₂₇-C₂₉△5-sterol and 5a-stanol in sections of 0~10cm and 20~30cm of QH core, and 0~20cm and 40~60cm of QG core provide indirect evidence for a sterol hydrogenation process in the sediment rather than a sediment input of both saturated and unsaturated sterols. The fact that the changes of saturated sterols/unsaturated sterols ratios(C₂₇-C₂₉ 5a-stanol/△5-sterol and △22-/△5,22ratios) are most pronounced in near-surface and the -uppermost sediment layers of QG and QH cores suggests that microorganisms are involved in the hydrogenation process. The sterols initially incorporated into the lake sediments mainly originate from abundant higher plants in the lake area and algae etc. in the lake water. An considerable increase in concentration of 5a-chelestanol in 80~100cm and 120~140cm sections of QG sediment core may reflect special organism ( ostracodes)contribution to the two section sediments.