• 责任者：Song Mu (Department of Earth Sciences ; University of Hong Kong ; Hong Kong ; China) ; Liu Weiguo
• 刊名：Quaternary Sciences
• 出版年：2013
• 卷期：33(6)
• 关键词：全新世 ; Holocene ; 湖泊沉积物 ; lake sediments ; 西北地区 ; North West China
• 页码：p.1199-1210
• 图表：5 illus., 79 refs.
• 分类号：1400
• issnNo：ISSN1001-7410
• isbnNo：CN11-2708/P

     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 （UK37）have been used to quantitatively reconstruct paleotemperature during the Holocene episode. However, UK37 values from the same climate event, especially the warm period, differ substantially in various lakes. Extremely high UK37 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 UK37 in westerlies controlled regions, organic geochemical analysis was employed on Late Holocene lacustrine sediments from 3 cores （MLll-C ll6cm, MLll-I 170cm and MLll-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.  UK37 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 ML1 l-I, 0.08 - 0.35 for core ML11-M ） and thus, different estimated temperature changes. High UK37 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 UK37 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 UK37 records from Manas Lake, Hurleg Lake, Gahai Lake,Sugan Lake and Qinghai Lake,indicates that the high UK37 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 UK37 values. First, when the lake was shallow, the environment became inappropriate for the preservation of alkenones and the UK37 value was exaggerated as a result of preferential degradation. Further, shallow waters were easier to be heated than deep waters and UK37 actually recorded the warm temperature of shallow waters. Thus we suggest that when the lake is stable with a relatively high lake level, UK37 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.