δD values of n-alkanes in Tibetan lake sediments and aquatic macrophytes - A surface sediment study and application to a 16 ka record from Lake Koucha
δD values of n-alkanes in Tibetan lake sediments and aquatic macrophytes - A surface sediment study and application to a 16 ka record from Lake Koucha
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DOI：
10.1016/j.orggeochem.2010.05.010
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发表时间：
2010-08-01
影响因子：
3
通讯作者：
Boehner, Juergen
中科院分区：
文献类型：
--
作者：
Aichner, Bernhard;Herzschuh, Ulrike;Boehner, Juergen
对青藏高原东部和中部湖泊表层沉积物和水生植物样品以及西藏高原东北部口岔湖沉积物柱样中脂肪族脂类生物标志物的氢同位素信号进行了分析。正构烷烃的δ D值与大气降水在夏季月份，并表现出增加皮尔逊相关系数增加正构烷烃链长（r，0.80的n-C-31）。而在最潮湿地区的样本中（青藏高原东南部），大气降水和脂类的表观富集因子与其它湿润地区的结果接近（对于中链正构烷烃，约为-135%，对于长链正构烷烃，约为-125ppm），它们变得更小在具有负水分平衡的站点（青藏高原东北部和中部以及柴达木盆地），平均值约为-118 ‰至-41 ‰;平均值为-86 ‰。这可能是由于湖水蒸发、土壤和叶水蒸散导致脂质合成水源水中氘的富集所致。在核心口岔湖，减少三角洲D值的所有正构烷烃之间的15和10 cal ka BP亚洲夏季风的加强提供了证据。在约9 cal ka BP，a ca. 15千分之一的中链正构烷烃向更高的三角洲D值的转移表明，湖水的蒸发增强，这超过了更高的降水量，因为在全新世早期季风最大的温度升高。只有少数表层沉积物样品显示中链正构烷烃和n-C-31的Δ D值之间存在显著的偏移（Δ Dmid-n-C31），这种偏移与环境参数（如年平均降水量）之间没有系统的相关性。在岩心中，大多数样品的可用数据也没有显示出显著的偏移，在约10.0 cal ka BP时，Delta Delta Dmid-n-C31仅略有增加（约为+15 ‰），而在约6.8 cal ka BP时，Delta Dmid-n-C31则有所减少（约为-17 ‰），这可能分别表明了较湿润和较干燥的条件。然而，由于核心关键部分缺乏n-C31的可靠数据，因此很难解释整个记录中的Delta Delta Dmin-n-C31。因此，更多的记录是必要的，以进一步测试三角洲三角洲Dmin-n-C31作为古水文条件的替代品的潜在适用性。(C)2010爱思唯尔有限公司版权所有。
A set of lake surface sediment samples and aquatic macrophytes from the eastern and central Tibetan Plateau and a sediment core from Koucha Lake (northeastern Tibetan Plateau) were analysed for hydrogen isotope signals of aliphatic lipid biomarkers. The delta D values of n-alkanes were correlated with those of meteoric water in the summer months and showed increasing Pearson correlation coefficients with increasing n-alkane chain length (r, 0.80 for n-C-31). While in samples from the most humid regions (southeastern Tibetan Plateau), the apparent enrichment factors between meteoric water and lipids are close to those reported for other humid sites (epsilon approximate to -135%o for mid-chain and approximate to -125 parts per thousand for long chain n-alkanes), they become smaller (epsilon approximate to -118 parts per thousand to -41 parts per thousand; mean value: -86 parts per thousand) at sites with a negative moisture balance (northeastern and central Tibetan Plateau and Qaidam Basin). This might be caused by enrichment in deuterium of the source water used for lipid synthesis as a result of lake water evaporation and soil and leaf water evapotranspiration. In the core from Lake Koucha, decreasing delta D values of all n-alkanes between 15 and 10 cal ka BP give evidence for an intensification of the Asian summer monsoon. At ca. 9 cal ka BP, a ca. 15 parts per thousand shift towards higher delta D values of mid-chain n-alkanes suggests enhanced evaporation of the lake water, which outweighs higher precipitation amounts because of a temperature increase during the early Holocene monsoonal maximum. Only a few surface sediment samples show a significant offset between delta D values of mid-chain n-alkanes and n-C-31 (A delta Dmid-n-C31) and no systematic dependence between this offset and environmental parameters, such as mean annual precipitation, was found. In the core, available data for most samples also do not show a significant offset, only a slight increase (approximate to + 15 parts per thousand) of Delta delta Dmid-n-C31 at ca 10.0 cal ka BP and a decrease (approximate to -17 parts per thousand) at ca 6.8 cal ka BP might indicate wetter and drier conditions, respectively. However, interpretation of Delta delta Dmin-n-C31 throughout the record is difficult because of a lack of reliable data for n-C31 in key sections of the core. So, more records are necessary to further test the potential applicability of Delta delta Dmin-n-C31 as a proxy for palaeo-hydrological conditions. (C) 2010 Elsevier Ltd. All rights reserved.