干旱区生态环境知识资源中心(Arid): 青藏高原干旱区湖泊正构烷烃氢同位素记录降水同位素

Arid

	青藏高原干旱区湖泊正构烷烃氢同位素记录降水同位素
其他题名	Sedimentary n-alkanes record of precipitation D/H ratios in arid regions of the Tibetan Plateau
	田茜; 方小敏; 王明达
来源期刊	科学通报
ISSN	0023-074X
出版年	2017
卷号	62 期号:7 页码:700-710
中文摘要	湖泊和海洋沉积物中正构烷烃氢同位素作为有潜力的古水文和古气候指标已经得到广泛应用, 但是在干旱区由于蒸发强烈而严重影响正构烷烃氢同位素比值, 因此其能否记录降水同位素变化受到质疑. 本研究在青藏高原干旱区采集了21个湖泊表层沉积物(其中20个湖泊年平均降水量<400 mm), 发现其正构烷烃氢同位素(deltaD_(wax))与年均降水平均氢同位素(deltaD_(ann))呈现较强相关(r~2=0.84, P<0.001), 其与夏季降水平均氢同位素(deltaD_(sum))相关性更好(r~2=0.91, P<0.001), 说明降水是控制湖泊沉积物中正构烷烃氢同位素(deltaD_(wax))变化的主要因素, 在干旱地区正构烷烃氢同位素(deltaD_(wax))仍然可以反映降水氢同位素(deltaD_p)信息. 本研究中湖泊表层沉积物正构烷烃和降水之间的氢同位素表观分馏平均值(epsilon_(wax-p))为-113, 较湿润地区偏正, 可能是由于干旱区蒸发强烈引起. 因此沉积正构烷烃氢同位素(deltaD_(wax))可以作为夏季降水平均氢同位素(deltaD_p)的替代指标, 记录夏季风强度和古水文变化.
英文摘要	The hydrogen isotope ratios of sedimentary leaf waxes have been investigated in various environments and are considered as a promising proxy for paleohydrological and paleoclimatic reconstruction. However, there is a growing concern regarding whether or not sedimentary leaf waxes can be used as an environmental proxy in extremely arid regions, where intensified evaporation strongly enriches the deuterium both in water and in leaf waxes. Here we present a record of the n-alkane D/H ratios of surface sediments from 21 lakes. The data were collected from 2012-2014. The n-alkanes extracted from lake surface sediments range from nC_(16) to nC_(35), with the most abundant compounds being nC_(23), nC_(25), nC_(29) and nC_(31). In addition, there is an evident odd-over-even preference for long-chain n-alkanes, with carbon preference index (CPI) values varying between 3.41 and 10.75, suggesting that the long-chain sedimentary n-alkanes mainly originated from terrestrial plants in arid regions on the Tibetan Plateau. The D/H ratios of the precipitation (deltaD_p) at all the lakes in this study were calculated using the Online Isotopes in Precipitation Calculator. The OIPC calculates precipitation isotope ratios at a given site by combining an empirical model for isotopic trends related to latitude and altitude with detrended interpolation based on the isotope data from stations in the Global Network of Isotopes in Precipitation. The mean annual hydrogen isotopes ratios of precipitation (deltaD_(ann)) at the lakes in this study vary from -78 to -115, with lower precipitation deltaD values occurring in the southern TP and higher values in the northern TP and the Qaidam Basin. The deltaD values for summer precipitation (July-September, deltaD_(sum)) range from -68 to -126, with a similar range of variation for deltaD_(ann). The sedimentary n-alkane D/H ratios are strongly correlated with the D/H ratios of annual precipitation (r~2=0.84) and summer precipitation (r~2=0.91), suggesting that the hydrogen isotope signal in sedimentary n-alkanes is mainly derived from precipitation, and that the n-alkane D/H ratios may reflect the D/H ratios of precipitation in arid regions on the Tibetan Plateau. Water is the ultimate source of hydrogen in plant tissues, and organic matter derived from terrestrial plants should record the isotopic ratio of soil water, which is ultimately recharged by precipitation. The deltaD values of n-alkanes in lake surface sediments could thus be expected to be correlated with the deltaD values of precipitation, on a large spatial scale. Furthermore, precipitation on the Tibetan Plateau mainly occurs from July to September, which accounts for ~70% during the year, and the n-alkanes of leaf wax are synthesized during the plant growing season. Therefore, it is unsurprising that the best correlation between D/H ratios of sedimentary leaf wax and precipitation occurs in the summer months. The apparent hydrogen isotopic fractionation between sedimentary n-alkanes and precipitation averages -113, evidently smaller than that in relatively humid regions. A possible reason for the smaller apparent fractionation might be spatial differences in soil evaporation and plant transpiration. Mean annual precipitation amount and mean annual evaporation at the studied lakes is 207 and 2343 mm, respectively. However, in the humid areas, such as the southeastern TP, the mean annual precipitation amount and mean annual evaporation are 1298 and 795 mm, respectively. Due to the strong evaporation in arid regions, the deltaD values of soil water and plant water are more isotopically-enriched relative to precipitation than those in humid regions. Overall, our results demonstrate that sedimentary n-alkanes can be used as a proxy indicator of variations in the isotopic composition of summer precipitation, in order to document past changes in summer monsoon intensity and hydrology.
中文关键词	青藏高原 ; 干旱地区 ; 表层沉积物 ; 降水 ; 正构烷烃 ; 氢同位素
英文关键词	Tibetan Plateau arid regions surface sediments precipitation n-alkane hydrogen isotopes
类型	Article
语种	中文
国家	中国
收录类别	CSCD
WOS类目	Geology
WOS研究方向	Geology
CSCD记录号	CSCD:5962954
资源类型	期刊论文
条目标识符	http://119.78.100.177/qdio/handle/2XILL650/236233
作者单位	田茜, 中国科学院青藏高原研究所, 中国科学院环境变化与地表过程重点实验室, 北京 100101, 中国.; 王明达, 中国科学院青藏高原研究所, 中国科学院环境变化与地表过程重点实验室, 北京 100101, 中国.; 方小敏, 中国科学院青藏高原研究所, 中国科学院大陆碰撞与高原隆升重点实验室;;中国科学院青藏高原地球科学卓越创新中心, 北京 100101, 中国.
推荐引用方式 GB/T 7714	田茜,方小敏,王明达. 青藏高原干旱区湖泊正构烷烃氢同位素记录降水同位素[J],2017,62(7):700-710.
APA	田茜,方小敏,&王明达.(2017).青藏高原干旱区湖泊正构烷烃氢同位素记录降水同位素.科学通报,62(7),700-710.
MLA	田茜,et al."青藏高原干旱区湖泊正构烷烃氢同位素记录降水同位素".科学通报 62.7(2017):700-710.