干旱区生态环境知识资源中心(Arid): 西北干旱区湖泊沉积物中长链烯酮的古环境意义

Arid

	西北干旱区湖泊沉积物中长链烯酮的古环境意义
其他题名	PALEOENVIRONMENTAL IMPLICATIONS OF LONG CHAIN ALKENONES IN ARID REGIONS, NORTHWESTERN CHINA
	宋木 1; 刘卫国 2; 郑卓 3; 柳中晖 1
来源期刊	第四纪研究
ISSN	1001-7410
出版年	2013
卷号	33 期号:6 页码:1199-1210
中文摘要	近年来,U_(37)~K长链烯酮古温度指标已被越来越多地应用于湖泊沉积物的研究中。综合分析我国西风区的湖泊沉积物记录,U_(37)~K对全新世暖期的记录存在较大差异,甚至有高达0.9的异常值出现,即湖泊表层水温在全新世超过30°C,这在气候意义上很难解释。为了更好地理解U_(37)~K在西北干旱区湖泊沉积物中的应用条件,文章对玛纳斯湖西岸的三处晚全新世湖滨沉积物钻孔进行了有机地球化学分析,首次确认了新疆玛纳斯湖湖泊沉积物中存在长链烯酮。通过分析U_(37)~K记录与长链烯酮含量的关系,并与其他西风区湖泊烯酮记录进行对比,发现长链烯酮的含量与干旱区湖泊的湖水位变化存在一定的关系,即长链烯酮含量的高低指示着湖水位的高低;同时,U_(37)~K记录与长链烯酮含量也存在一定的联系:异常高的U_(37)~K值总是伴随着较低的烯酮含量(<100ng/g干样),即产生于湖滨相或湖泊接近于干涸状态。由此,本文认为湖水位较低时,湖泊水体差异升温和长链烯酮的选择性分解可能是导致较高U_(37)~K出现的原因;这样的U_(37)~K记录是不可靠的,不能用于定量计算古温度,但仍可用于反应冷暖趋势的变化。
英文摘要	Long chain alkenones are found in lacustrine sediments of various kinds of lakes in Westerlies-controlled arid regions, Northwestern China. Long chain alkenone unsaturation index (U_(37)~(K’)) have been used to quantitatively reconstruct paleotemperature during the Holocene episode. However, U_(37)~(K’) values from the same climate event, especially the warm period, differ substantially in various lakes. Extremely high U_(37)~(K’) values (reaching up to 0.9) were discovered during warm periods, which is obviously difficult to be explained under the context of climatic changes. In order to understand the application of U_(37)~(K’) in westerlies controlled regions, organic geochemical analysis was employed on Late Holocene lacustrine sediments from 3 cores (ML11-C 116cm, ML11-I 170cm and ML11-M 152cm) which were retrieved from the shorelines of Manas Lake (45°45’N,86°00’E), Jungaar basin, in this study. Manas Lake is a large salt lake which is the terminal lake of Manas River. The lake dried up after 1960 because of agricultural use of water resource and build of dam. Modern climate of Manas Lake is mainly controlled by westerlies with mean annual temperature 7~8℃. The annual precipitation is only about 100~200mm/a while the annual evaporation 3110mm/a far exceeds the precipitation. The water source of precipitation is mainly from the west, the Atlantic Ocean and the Arctic. U_(37)~(K’) records from the three Late Holocene cores display different ranges of value changes(0.14~0.59 for core ML11-C,0. 13~0.38 for core ML11-I, 0.08~0.35 for core. ML11-M) and thus, different estimated temperature changes. High U_(37)~(K’) values are always concurrent with relatively low C37 alkenone contents (C37 < 100ng/g dry sample). As C37 contents vary in magnitude(from near 0 to tens of thousands ng/g dry sample), we interpret that relatively low C37 contents or no alkenones detected correspond to relatively low lake level or even dried-up conditions. Higher-than-normal U_(37)~(K’) values thus appear to be related to lake shore environments when lake level was extremely shallow or lake water only occasionally reached to the coring site. Further comparisons of Late Holocene U_(37)~(K’) records from Manas Lake, Hurleg Lake, Gahai Lake, Sugan Lake and Qinghai Lake,indicates that the high U_(37)~(K’) values were highly exaggerated when lake level was low, thus could not be used to estimate temperatures quantitatively. Two factors might explain the extremely high U_(37)~(K’) values. First, when the lake was shallow, the environment became inappropriate for the preservation of alkenones and the U_(37)~(K’) value was exaggerated as a result of preferential degradation. Further, shallow waters were easier to be heated than deep waters and U_(37)~(K’) actually recorded the warm temperature of shallow waters. Thus we suggest that when the lake is stable with a relatively high lake level, U_(37)~(K’) values could be quantitatively used in temperature reconstruction, while the high values recorded in a shallow unstable lake could only be used qualitatively in Westerly-controlled arid regions.
中文关键词	干旱区 ; 湖泊沉积物 ; 长链烯酮 ; 湖水位 ; 古温度重建
英文关键词	arid region lacustrine sediment long chain alkenones lake level paleotemperature reconstruction
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:4988785
资源类型	期刊论文
条目标识符	http://119.78.100.177/qdio/handle/2XILL650/229433
作者单位	1.香港大学地球科学系, 香港; 2.中国科学院地球环境研究所, 黄土与第四纪地质国家重点实验室, 西安, 陕西 710075, 中国; 3.中山大学地球科学系, 广州, 广东 510275, 中国
推荐引用方式 GB/T 7714	宋木,刘卫国,郑卓,等. 西北干旱区湖泊沉积物中长链烯酮的古环境意义[J],2013,33(6):1199-1210.
APA	宋木,刘卫国,郑卓,&柳中晖.(2013).西北干旱区湖泊沉积物中长链烯酮的古环境意义.第四纪研究,33(6),1199-1210.
MLA	宋木,et al."西北干旱区湖泊沉积物中长链烯酮的古环境意义".第四纪研究 33.6(2013):1199-1210.