青藏高原中部色林错湖泊沉积物色度反映末次冰盛期以来区域古气候演化
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摘要
色林错湖位于青藏高原内部,是西藏第一大咸水内陆湖。研究区剖面选自色林错第三湖泊阶地,利用常用气候替代指标色度,结合粒度、碳酸盐含量[CaCO_3(%)]、矿物分析和全有机质(TOC)等进行对比分析,同时采用~(14)C测年方法对剖面进行准确的年代划分,初步探讨了末次冰盛期以来色林错湖泊沉积物色度增强机制的差异性。研究表明:a~*、b~*与中粗粒砂、磁化率具有较好的相关性;亮度L~*与CaCO_3(%)具较好相关性;因而沉积物色度变化可反应区域古气候变化。同时对湖泊沉积物矿物分析发现,影响色度变化的制色矿物主要是针铁矿,且以还原环境为主。红度a~*高值与亮度L~*低值对应气候暖湿气候环境,沉积物粒度较粗,碳酸盐含量低,有机质含量高,磁化率较高值;反之,红度a~*低值,L~*高值,粒度较细,碳酸盐含量高,有机质含量低,磁化率低值,对应干冷气候。在17.4～15.5 cal ka BP阶段,对应干冷的气候特点;在15.5～10.4 cal ka BP阶段,对应温暖湿润的气候;在10.4～5.2 cal ka BP阶段,整体属于温暖湿润的气候特点;其中,在9.7～9.4 cal ka BP和8.75～8.5 cal ka BP为两个重要的冷事件,属于干湿的气候特点;在5.2～1.2 cal ka BP阶段,反映了干冷的气候特征;在4.3～4.0 cal ka BP,3.3～3.0 cal ka BP和2.4～1.75 cal ka BP,反映了干旱温暖的气候特点;在1.2 cal ka BP以后,色林错湖湖水迅速下降。
The Selin Co Lake is located in the central Qinghai-Tibetan Plateau,China,which is a sensitive region to climate. Meanwhile,the area is less influenced by human activities.In recent years,the region became a hotspot for the paleoenvironmental research community.In this paper,the profile is selected in the third terrace of the lakeshore and 122 samples were collected there.By using ~(14)C dating method,we get the exact age of the profile.The combination of many different methods,such as TOC,X-ray diffraction(XRD),CaCO_3(%),magnetic susceptibility and grain size,were used to investigate the paleo-environment.Three components were considered in this investigation including red(a~*),yellow(b~*) and brightness(L~*).The a~* and b~* are mainly related to the value of goethite and the a~* in sediment is primarily related to wet-warm climate,which can be used to monitor paleoclimatic changes in the area.The L~* has a good correlation with TOC and CaCO_3(%); and almost has correlation with magnetic susceptibility and grain size.If the grain size of the lake sediment became coarser,magnetic susceptibility was bigger,the organic content went higher,and the CaCO_3(%) got decreased,all these indicated the climate was in the warm-wet condition which was reflected by a higher a~* value and a lower L~* value; otherwise,the climate was in the cold-dry condition which was reflected by a lower a~* value and a higher L~* value.Therefore,the paleoclimatic changes were divided into 5 stages: The cold-dry climatic period from 13.33 to 12.23 ka BP,the significant cold-dry climatic period from 12.23 to 10.07 ka BP when the Younger Dryas event occurred,the Holocene Megathermal period from 10.68 to 8.70 ka BP when the values of a~* and b~* kept higher and the value of L~* sustained a dropping trend,the warm-wet climatic period from 8.70 to 3.93 ka BP and the cold-dry climatic period from 3.93 to 0 ka BP.The result was very similar to the monsoon changes in Qinghai-Tibetan Plateau.
The Selin Co Lake is located in the central Qinghai-Tibetan Plateau,China,which is a sensitive region to climate. Meanwhile,the area is less influenced by human activities.In recent years,the region became a hotspot for the paleoenvironmental research community.In this paper,the profile is selected in the third terrace of the lakeshore and 122 samples were collected there.By using ~(14)C dating method,we get the exact age of the profile.The combination of many different methods,such as TOC,X-ray diffraction(XRD),CaCO_3(%),magnetic susceptibility and grain size,were used to investigate the paleo-environment.Three components were considered in this investigation including red(a~*),yellow(b~*) and brightness(L~*).The a~* and b~* are mainly related to the value of goethite and the a~* in sediment is primarily related to wet-warm climate,which can be used to monitor paleoclimatic changes in the area.The L~* has a good correlation with TOC and CaCO_3(%); and almost has correlation with magnetic susceptibility and grain size.If the grain size of the lake sediment became coarser,magnetic susceptibility was bigger,the organic content went higher,and the CaCO_3(%) got decreased,all these indicated the climate was in the warm-wet condition which was reflected by a higher a~* value and a lower L~* value; otherwise,the climate was in the cold-dry condition which was reflected by a lower a~* value and a higher L~* value.Therefore,the paleoclimatic changes were divided into 5 stages: The cold-dry climatic period from 13.33 to 12.23 ka BP,the significant cold-dry climatic period from 12.23 to 10.07 ka BP when the Younger Dryas event occurred,the Holocene Megathermal period from 10.68 to 8.70 ka BP when the values of a~* and b~* kept higher and the value of L~* sustained a dropping trend,the warm-wet climatic period from 8.70 to 3.93 ka BP and the cold-dry climatic period from 3.93 to 0 ka BP.The result was very similar to the monsoon changes in Qinghai-Tibetan Plateau.
引文
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[6] VAN CAMPO E,GASSE F.Pollen-and diatom-inferred climatic and hydrological changes in Sumxi Co Basin (Western Tibet) since 13 000 yr BP[J].Quaternary Research,1993,39(3):300-313.
[7] GU Z Y,LIU J L,YUAN B Y,et al.Monsoon variations of the Qinghai-Xizang Plateau during the last 12 000 years:Geochemical evidence from the sediments in the Siling Lake[J].Science Bulletin,1993,38:577-581.
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[10] 薛蕾,张振卿,刘维明,等.西藏色林错12 ka以来的湖泊退缩过程——基于古湖岸线的OSL测年[J].地质科学,2010,45(2):428-439.[XUE Lei,ZHANG Zhenqing,LIU Weiming,et al.The shrinking process of Siling Co in the past 12 ka:Based on OSL dating of past shorelines[J].Chinese Journal of Geology,2010,45(2):428-439.]
[11] 赵希涛,赵元艺,郑绵平,等.班戈错晚第四纪湖泊发育、湖面变化与藏北高原东南部末次大湖期湖泊演化[J].地球学报,2011,32(1):13-26.[ZHAO Xitao,ZHAO Yuanyi,ZHENG Mianping,et al.Late quaternary lake development and denivellation of Bankog Co as well as lake evolution of southeastern north Tibetan Plateau during the last great lake period[J].Acta Geoscientia Sinica,2011,32(1):13-26.]
[12] 林勇杰,郑绵平,王海雷.青藏高原中部色林错矿物组合特征对晚全新世气候的响应[J].科技导报,2014,32(35):35-40.[LIN Yongjie,ZHENG Mianping,WANG Hailei.Late Holocene climatical and environmental evolutions inferred from mineralogical records in Selin Co,Central Qinghai-Tibetan Plateau[J].Science and Technology Review,2014,32(35):35-40.]
[13] 王海雷,郑绵平.青藏高原中部色林错SL-1孔粒度参数指示的5.33 ka BP以来的水位变化[J].科技导报,2014,32(35):29-34.[WANG Hailei,ZHENG Mianping.Lake level changes indicated by grain-size of core SL-1 sediments since 5.33 ka BP in Selin Co,central Qinghai-Tibetan Plateau [J].Science and Technology Review,2014,32(35):29-34.]
[14] NAGAO S,NAKASHIMA S.The factors controlling vertical color variations of North Atlantic Madeira Abyssal Plain sediments[J].Marine Geology,1992,109(1-2):83-94.
[15] HELMKE J P,SCHULZ M,BAUCH H A.Sediment-color record from the Northeast Atlantic reveals patterns of millennial-scale climate variability during the past 500 000 years[J].Quaternary Research,2002,57(1):49-57.
[16] BALSAM W L,DEATON B C,DAMUTH J E.Evaluating optical lightness as a proxy for carbonate content in marine sediment cores[J].Marine Geology,1999,161(2-4):141-153.
[17] 吴健,沈吉.兴凯湖沉积物磁化率和色度反映的28 ka BP以来区域古气候环境演化[J].海洋地质与第四纪地质,2009,29(3):123-131.[WU Jian,SHEN Ji.Paleoenvironmental and paleoclimatic changes reflected by diffuse reflectance spectroscopy and magnetic susceptibility from Xingkai Lake sediments[J].Marine Geology and Quaternary Geology,2009,29(3):123-131.]
[18] 林瑞芬,卫克勤.新疆玛纳斯湖沉积物氧同位素记录的古气候信息探讨——与青海湖和色林错比较[J].第四纪研究,1998,18,(4):308-318.[LIN Ruifen,WEI Keqin.Palaeoclimate implications of oxygen isotope record from lacustrine sediments of Manas Lake,Xinjiang:A comparison with those from Qinghai Lake and Siling Lake[J].Quaternary Sciences,1998,18(4):308-318.]
[19] 严永耀,安聪荣,苗运法,等.新疆青海地区现代地表沉积物颜色指标与气候参数关系[J].干旱区地理,2017,40(2),355-364.[YAN Yongyao,AN Congrong,MIAO Yunfa,et al.Relationship between color index of modern surface sediment and climate parameters in the region of Xinjiang and Qinghai[J].Arid Land Geography,2017,40(2),355-364.]
[20] 章云霞,叶玮,马春梅,等.浙江北湖桥孔色度记录的早-中全新世环境变化[J].第四纪研究,2016,36(5),1331-1342.[ZHANG Yunxia,YE Wei,MA Chunmei,et al.Environment variabilities archived by color of the drill core Beihuqiao in Hangjiahu Plain during the Early-Mid Holocene,China[J].Quarternary Sciences,2016,36(5),1331-1342.]
[21] 吴艳宏,李世杰.湖泊沉积物色度在短尺度古气候研究中的应用.地球科学进展,2004,19(5):789-792.[WU Yanhong,LI Shijie.Significance of lake sediment color for short time scale climate variation[J].Advance in Earth Sciences,2004,19(5):789-792.]
[22] 王永,姚培毅,迟振卿,等.内蒙古浩来呼热湖泊沉积物色度记录的末次冰消期以来的环境演变[C]//第十二届全国古地理学及沉积学学术会议论文摘要集,2012:1.[WANG Yong,YAO Peiyi,CHI Zhenqing,et al.Environmental variabilities archived by color of sediment in Laihure Lake of Neimonggu during MIS 3 [C]//Summary of Papers of the Twelfth National Academic Conference on Paleogeography and Sedimentology,2012:1.]
[23] 田庆春,杨太保,石培宏,等.可可西里BDQ0608钻孔沉积物色度环境意义及其影响因素[J].海洋地质与第四纪地质,2012,32(2):133-140.[TIAN Qingchun,YANG Taibao,SHI Peihong,et al.Environmental implication of color reflectance of drill hole BDQ0608,Keke Xili region and its influencing factors[J].Marine Geology and Quaternary Geology,2012,32(1):133-140.]
[24] 陈杰,杨太保,曾彪,等.中国帕米尔地区黄土磁化率特征及其影响因素[J].干旱区地理,2016,39(4),761-769.[CHEN Jie,YANG Taibao,ZENG Biao,et al.Magnetic susceptibility features and influencing factors in Pamir,China[J].Arid and Geography,2016,39(4):761-769.]
[25] 关志华,陈传友,区裕熊,等.西藏河流与湖泊[M].北京:科学出版社.1984:82-89.[GUAN Zhihua,CHEN Chuanyou,QU Yuxiong,et al.Rivers and Lakes in Tibet[M].Beijing:Sciences Press,1984:82-89.]
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