青海湖晚第四纪的古环境演化和湖面变化是学术界长期关注的热点问题，争议也较多。我们对青海湖地区种羊场（ZYC）剖面（120 cm厚）全新世风尘堆积的GDGTs （甘油二烷基甘油四醚）化合物相关指标的古环境意义进行了初步研究，以期从一...青海湖晚第四纪的古环境演化和湖面变化是学术界长期关注的热点问题，争议也较多。我们对青海湖地区种羊场（ZYC）剖面（120 cm厚）全新世风尘堆积的GDGTs （甘油二烷基甘油四醚）化合物相关指标的古环境意义进行了初步研究，以期从一个新的角度对上述问题进行探讨。研究结果表明：1） ZYC剖面的TEX86（由86个碳原子组成的四醚指标）与磁化率正相关，而Ri/b比值（类异戊二烯GDGTs与支链GDGTs丰度的比值）与磁化率负相关。2） ZYC剖面的TEX86指标与湖泊岩芯胖真星介（Eucypris inflata）壳体δ18O指示的7月古水温及长链烯酮（U37K）指示的夏季古水温变化具有相似的变化特征，显示TEX86指标较可靠地指示了青海湖地区的大气温度变化。然而，ZYC剖面的MBT （甲基化指数）和CBT （环化指数）指标在重建古气温方面具有一定的局限性，可能与青海湖地区全新世出现的干旱环境有关。3） ZYC剖面的Ri/b比值与湖泊岩芯E.inflata壳体Sr/Ca比值指示的青海湖湖水的古盐度具有较一致的变化特征，表明Ri/b比值较有效地指示了青海湖地区环境的干湿状况。4） TEX86和Ri/b指标揭示青海湖区在9.5~7.5 ka B.P.为冷干时期；7.5~5.5 ka B.P.为独特的温干阶段，温度在6.2 ka B.P.左右达到最高值；5.5~1.7 ka B.P.为温湿时期；1.7~0 ka B.P.为冷干时期。5）风尘堆积的GDGTs记录表明：7.5~5.5 ka B.P.由于环境干旱，青海湖不太可能出现高湖面；5.5~1.7 ka B.P.由于环境湿润，青海湖很可能出现全新世高湖面；1.7 ka B.P.以来，青海湖地区的气候快速变干。展开更多
Isoprenoid and branched glycerol dialkyl glycerol tetraethers （GDGTs） lipids were studied in flooded and non-flooded paddy soil in Wuhan, central China, to examine the response of the GDGTs distribution to the soil ...Isoprenoid and branched glycerol dialkyl glycerol tetraethers （GDGTs） lipids were studied in flooded and non-flooded paddy soil in Wuhan, central China, to examine the response of the GDGTs distribution to the soil flooding. Samples were collected before and after the soil flooding in four specific months. Both core （CL） and intact polar （IPL） GDGTs were quantified. Increase in the abundance of archaeol and caldarchaeol may be indicative of the occurrence of methanogens in the flooded soil. A negative correlation was observed between the ratio of IPL branched GDGT-IIa to GDGT-Ia and the soil pH. The rise of the soil pH in the acid soil is known to be controlled by the redox conditions resulting from flooding. Thus, the branched GDGTs distribution may be controlled by the water content in the paddy soil. In addition, we suggest that the anoxic conditions resulting from flooding may also control the abundance of branched GDGTs relative to crenarchaeol, which in turn results in the increase of branched and isoprenoidal tetraethers （BIT） values, the index for the terrestrial input to the marine sediments.展开更多
文摘异戊二烯类甘油二烷基甘油四醚脂类化合物(isoprenoid Glycerol dialkyl glycerol tetraethers,isoGDGTs)在海洋奇古菌(Thaumarchaeota)中广泛存在,其结构对温度变化的敏感性使其成为广受欢迎的古气候与古温度重建材料。在北冰洋和西太平洋气候以及黑潮等多种因素的影响下,冲绳海槽中部成为研究全新世以来古海洋和古气候变化的天然实验室。本文通过研究C14柱状沉积物的GDGTs组成、含量变化特征及其延伸的86个碳原子的四醚指标(tetraether index of tetraethers consisting of 86 carbons,TEX86H),分析冲绳海槽中部的GDGTs来源,并定量计算C14柱状沉积物记录的海洋表面温度(seasurfacetemperature,SST),从而探讨8.2ka以来冲绳海槽中部古温度变化的驱动机制。通过甲烷指数和支链/异戊二烯类指标等,我们确认isoGDGTs主要来自于氨氧化古菌,适用于古温度重建。距今8.2ka以来,TEX86H SST的变化范围是21.6~27.2℃。冲绳海槽中部SST主要受到西热带太平洋、低纬度冬季日晒量的影响;TEX86H指标记录的温度上升趋势与东亚夏季风强度的减弱不一致。7.4—6.6ka冷事件广泛存在于冲绳海槽的SST记录中,但只在TEX86H数据中显示较大幅度的降低(~5℃),我们推测可能受到Kikai-Akahoya火山灰(~7.3ka)的影响。
文摘青海湖晚第四纪的古环境演化和湖面变化是学术界长期关注的热点问题，争议也较多。我们对青海湖地区种羊场（ZYC）剖面（120 cm厚）全新世风尘堆积的GDGTs （甘油二烷基甘油四醚）化合物相关指标的古环境意义进行了初步研究，以期从一个新的角度对上述问题进行探讨。研究结果表明：1） ZYC剖面的TEX86（由86个碳原子组成的四醚指标）与磁化率正相关，而Ri/b比值（类异戊二烯GDGTs与支链GDGTs丰度的比值）与磁化率负相关。2） ZYC剖面的TEX86指标与湖泊岩芯胖真星介（Eucypris inflata）壳体δ18O指示的7月古水温及长链烯酮（U37K）指示的夏季古水温变化具有相似的变化特征，显示TEX86指标较可靠地指示了青海湖地区的大气温度变化。然而，ZYC剖面的MBT （甲基化指数）和CBT （环化指数）指标在重建古气温方面具有一定的局限性，可能与青海湖地区全新世出现的干旱环境有关。3） ZYC剖面的Ri/b比值与湖泊岩芯E.inflata壳体Sr/Ca比值指示的青海湖湖水的古盐度具有较一致的变化特征，表明Ri/b比值较有效地指示了青海湖地区环境的干湿状况。4） TEX86和Ri/b指标揭示青海湖区在9.5~7.5 ka B.P.为冷干时期；7.5~5.5 ka B.P.为独特的温干阶段，温度在6.2 ka B.P.左右达到最高值；5.5~1.7 ka B.P.为温湿时期；1.7~0 ka B.P.为冷干时期。5）风尘堆积的GDGTs记录表明：7.5~5.5 ka B.P.由于环境干旱，青海湖不太可能出现高湖面；5.5~1.7 ka B.P.由于环境湿润，青海湖很可能出现全新世高湖面；1.7 ka B.P.以来，青海湖地区的气候快速变干。
基金We would thank Dr. WeiHua Ding for analytical assistance with the HPLC-MS equipment. This work was supported by the National Basic Research Program of China （No. 2011CB808800）, the National Natural Science Foundation of China （Grant Nos. 40930210 and 40921062） and the 111 program （B08030） in China.
文摘Isoprenoid and branched glycerol dialkyl glycerol tetraethers （GDGTs） lipids were studied in flooded and non-flooded paddy soil in Wuhan, central China, to examine the response of the GDGTs distribution to the soil flooding. Samples were collected before and after the soil flooding in four specific months. Both core （CL） and intact polar （IPL） GDGTs were quantified. Increase in the abundance of archaeol and caldarchaeol may be indicative of the occurrence of methanogens in the flooded soil. A negative correlation was observed between the ratio of IPL branched GDGT-IIa to GDGT-Ia and the soil pH. The rise of the soil pH in the acid soil is known to be controlled by the redox conditions resulting from flooding. Thus, the branched GDGTs distribution may be controlled by the water content in the paddy soil. In addition, we suggest that the anoxic conditions resulting from flooding may also control the abundance of branched GDGTs relative to crenarchaeol, which in turn results in the increase of branched and isoprenoidal tetraethers （BIT） values, the index for the terrestrial input to the marine sediments.
