西北干旱区湖泊沉积物中长链烯酮的古环境意义  

PALEOENVIRONMENTAL IMPLICATIONS OF LONG CHAIN ALKENONES IN ARID REGIONS,NORTHWESTERN CHINA

作　　者：宋木[1] 刘卫国[2] 郑卓[3] 柳中晖[1] 

机构地区：[1]香港大学地球科学系 [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710075 [3]中山大学地球科学系,广州510275

出　　处：《第四纪研究》2013年第6期1199-1210,共12页Quaternary Sciences

基　　金：香港研究资助局项目(批准号:HKU703809P);香港特别行政区大学教育资助委员会特别设备补助金项目(批准号:SEG_HKU01)共同资助

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℃,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。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 sho

关 键 词：干旱区 湖泊沉积物 长链烯酮 湖水位 古温度重建 

分 类 号：P593[天文地球—地球化学] P941.78[天文地球—地质学]