贵州草海近21 ka以来有机地球化学记录反映的古环境变化<sup>*</sup>

龚晓飞, 陈聪, 汤永杰, 黄康有, 乐远福, 梁凯璇, 郑卓. (2019)贵州草海近21 ka以来有机地球化学记录反映的古环境变化^* [J]. 古地理学报, 21(6): 1025-1034
Gong Xiao-Fei, Chen Cong, Tang Yong-Jie, Huang Kang-You, Yue Yuan-Fu, Liang Kai-Xuan, Zheng Zhuo. (2019)Palaeoenvironment changes during the past 21 ka inferred from organic geochemical records of Caohai Lake,Guizhou Province[J]. Journal Of Palaeogeography, 21(6): 1025-1034. 复制到剪切板

Doi: 10.7605/gdlxb.2019.06.070
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贵州草海近21 ka以来有机地球化学记录反映的古环境变化^*

龚晓飞¹, 陈聪¹, 汤永杰¹, 黄康有¹, 乐远福², 梁凯璇¹, 郑卓¹

1 中山大学地球科学与工程学院,广东广州 510275

2 广西大学海洋学院,广西南宁 530004

通讯作者简介郑卓,男,1956年生,教授,博士生导师,主要研究方向为第四纪古环境和全球气候变化研究。E-mail: eeszzhuo@mail.sysu.edu.cn。

第一作者简介龚晓飞,男,1993年生,硕士研究生,第四纪地质学专业。E-mail: gongxf5@mail2.sysu.edu.cn。

收稿日期:2018-08-04

基金资助:* 国家自然科学基金项目(编号: 41472143,41630753)资助

摘要

草海位于黔滇交界,主要受印度夏季风的影响,其湖沼沉积物记录了中—晚第四纪的环境变化历史,是研究第四纪环境和季风演变的良好载体。本研究选取的南屯 NT03钻孔,岩心长 405 cm,在放射性碳同位素( AMS¹⁴C)测年基础上建立了年代序列,并进行了沉积物的色差值( L^*)、烧失量( LOI550)、总有机碳( TOC)、碳氮比( C/N)和有机稳定碳同位素(δ13Corg)等古环境替代指标的测试。实验结果显示, L^*、 LOI550和 TOC等 3个有机碳含量指标同步变化,共同指示该钻孔序列经历了 3个沉积环境演变阶段,即末次盛冰期晚期( 21— 15 cal ka BP)河流—冲积相沉积阶段、冰消期至早中全新世( 15— 4 cal ka BP)高湖面湖泊—沼泽相沉积阶段和晚全新世( 4 cal ka BP以来)洪冲积相沉积阶段。近 2万年以来草海湖沼面积经历的收缩→扩张→收缩演变过程与石笋氧同位素变化基本吻合,表明季风降雨是引起草海湖泊水体和周边生态系统变化的主要因素。δ13Corg指标变化范围为- 29.28‰~- 24.19‰,表明草海盆地周围植被组成在末次盛冰期以来 C4草本虽然略有增加,但均以 C3植物为主。同时, TOC和δ13Corg指标证明了 B/A冰消期暖事件对盆地边缘区的湿地泥炭富集起到关键作用,而多指标揭示了近 4 ka以来水域变浅并发展成为冲积环境的过程,也可能与石笋记录的夏季风减弱所带来的降水量减少有关。

关键词: 贵州省; 草海; 印度夏季风; 沉积环境; 稳定碳同位素

中图分类号:P534.63 文献标志码:A 文章编号:1671-1505(2019)06-1025-10

Palaeoenvironment changes during the past 21 ka inferred from organic geochemical records of Caohai Lake,Guizhou Province

Gong Xiao-Fei¹, Chen Cong¹, Tang Yong-Jie¹, Huang Kang-You¹, Yue Yuan-Fu², Liang Kai-Xuan¹, Zheng Zhuo¹

1 School of Earth Sciences and Engineering,Sun Yat-sen University,Guangzhou 510275,China

2 School of Marine Sciences, Guangxi University,Nanning 530004,China

About the corresponding author Zheng Zhuo,born in 1956,is a professor at School of Earth Sciences and Engineering,Sun Yat-sen University. Now his research interests are Quaternary palaeoenvironmental evolution and global climate change. E-mail: eeszzhuo@mail.sysu.edu.cn.

About the first author Gong Xiao-Fei,born in 1993,is a master degree candidate. He majors in Quaternary geology in School of Earth Sciences and Engineering,Sun Yat-sen University. E-mail: gongxf5@mail2.sysu.edu.cn.

Fund:Financially supported by National Natural Science Foundation of China(Nos. 41472143,41630753)

Abstract

Caohai Lake is located in the boundary area between Guizhou and Yunnan provinces where the climate is dominated by Indian summer monsoon(ISM). The continuous lacustrine bog sediments provide ideal material for revealing middle and late Quaternary environmental changes. In this paper,a core of 405 cm length(NT03)was studied. The age model was established based on 7 AMS¹⁴C ages covering the last 21 ka. Here we present the results of sediment chromatic aberration value(CIE-L^*),loss on ignition at 550 ℃(LOI550),total organic carbon(TOC),C/N ratio and stable carbon isotope(δ13Corg). The environment proxies(L^*、TOC and LOI550)varied synchronously,indicating three distinct intervals of lake level since the Last Glacial Maximum(LGM),i.e. riverine alluvial facies,lake-wetland facies and shallow water alluvial facies respectively from 21~15 ka BP,15~4 cal ka BP and after 4 cal ka BP. This change pattern is similar to the variation of speleothem δ¹⁸O records from the south China. Theδ13Corg values,varying between-29.28‰ and-24.19‰,suggest C3 plant domination in regional vegetation,despite a possible moderate C4 plant increase during the LGM. The TOC andδ13Corg records show an important change at B/A event implying the local ecosystem and lake level are sensitive to the deglacial warming. There was an abrupt change in all proxy records at around 4 ka BP which may indicate a weakening summer monsoon indicated by the speleothem δ¹⁸O records.

Key words: Guizhou Province; Caohai Lake; Indian summer monsoon; depositional environment; stable carbon isotope

文章图片

印度季风作为亚洲季风的重要组成部分, 从热带印度洋携带大量水汽输送至南亚内陆形成季风降水, 对区域水文循环和生态系统产生重要影响(Zhang et al., 2017), 前人对印度季风在不同时间尺度上的演化历史、驱动机制及其生态响应进行了研究(An et al., 2011; Chen et al., 2014; Deplazes et al., 2014; Cai et al., 2015; Zhang et al., 2017; 沈吉和肖霞云, 2018)。研究认为南北半球共同影响印度季风(An et al., 2011)。印度季风带来的降水与西印度洋海表温度关系密切, 并与海陆水文循环存在重要联系(Zhang et al., 2017)。前人丰富的湖泊多指标古环境研究成果为西南地区的环境变化研究提供了重要认识, 但由于受印度季风影响的亚热带地区地形复杂, 地势起伏较大, 且生物多样性丰富(韩冰等, 2008), 不同地区的生态系统对于气候变化的响应机制和过程是否一致, 需要空间覆盖更密集的古环境记录进行对比研究。地处中国贵州的草海湿地属于高原湖沼沉积体系, 其沉积序列记录了丰富的自晚更新世以来的环境演变信息(陈佩英等, 1993; 朱正杰等, 2010; 孔凡翠等, 2013)。但之前关于有机碳同位素的研究存在年代框架精度较低(陈佩英等, 1993)或时间跨度较短(朱正杰等, 2010)等问题。本研究在草海盆地东南边缘的南屯湖沼沉积中获取了钻孔岩心, 在加速器质谱放射性碳同位素(AMS¹⁴C)测年的框架下, 根据沉积物色差值(L^*)、烧失量(LOI)、总有机碳(TOC)和有机稳定碳同位素( $δ^{13} C_{org}$ )等多种手段和指标, 深入探讨末次冰盛期(LGM)以来草海地区的环境演化及气候变化历史, 为西南地区的古环境研究提供新的佐证。

1 区域概况与钻孔特征

1.1 区域概况

草海盆地位于贵州省威宁彝族回族苗族自治县境内, 地处云贵高原, 该盆地受威宁弧形背斜控制, 为一山间盆地, 处于长江水系和珠江水系分水岭的古老夷平面之上(林树基和郑洪汉, 1987)。盆地内主要分布石炭系碳酸盐岩地层, 盆地周围主要为下二叠统。草海周围不发育地表河流, 也无远源河流汇入, 因此主要的水分来源是大气降水及其汇集形成的季节性溪流, 故湖泊水位主要受到降水影响。该地区主要受印度夏季风的影响, 属暖温带温凉气候类型, 年均降水量约为1000 mm, 主要集中在夏季, 冬、春季干旱少雨, 年均温10.5~11.3° C(Zhu et al., 2014)。盆地内第四系以湖沼相沉积为主, 其次也存在冲、洪积相和坡积相。湖沼相沉积主要分布于盆地中部草海湖区及附近谷地中, 主要由黏土和富有机质泥炭组成, 最大厚度可达85 m(林树基和郑洪汉, 1987)。文中所研究的NT03钻孔(26.8140° N, 104.3405° E, 2165 m)位于草海盆地的东南侧边缘(图1), 属于草海与簸箕湾之间的低洼地带。

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	图 1 贵州草海NT03钻孔位置 A— 区域地形及研究钻孔地理位置; 虚线代表夏季风边界; 数字1代表三星洞; 2代表泸沽湖; 3代表洱海; 4代表董哥洞; 5代表大湖。B— 草海湖盆沉积分布和NT03钻孔位置(据林树基和郑洪汉, 1987; 修改)Fig.1 Geographical location of Borehole NT03 from Caohai Lake, Guizhou Province

现今草海盆地及其周边的植被面貌以半湿润常绿落叶阔叶植物为主, 其中最为主要的是以华山松(Pinus armandii)、云南松(P. yunnanensis)为代表的针叶林, 以及以常绿、落叶栎为代表的常绿落叶阔叶林, 海拔较高处分布有中旱生山地草坡(Zhu et al., 2011)。根据《贵州植被》(黄威廉等, 1988)中的划分, 草海地区的植被垂直分带如下: 海拔小于 2400 m为黄棕壤分布区, 是常绿阔叶和少量针叶树种分布带, 主要的树种有马尾松(Pinus massoniana)、滇黄栎(Cyclobalanopsis delavayi)、滇青冈(Cyclobalanopsis glaucoides)、云南樟(Cinnamomum glanduliferum)、红木荷(Schima wallichii)等; 2400~2700 m为黄壤分布区, 是落叶阔叶和部分针叶树种分布带, 主要的树种有刺柏(Juniperus formosana)、华山松、云南松等针叶树种, 白栎(Quercus fabri)、槲栎(Quercus aliena)、滇榛(Corylus yunnanensis)、滇杨(Populus yunnanensis)、云南柳(Salix cavaleriei)和蒙自桤木(Alnus mengtze)等落叶阔叶树种; 大于2700 m为草甸土分布区, 植被类型为高山灌丛和草甸, 灌丛植物主要有杜鹃花科和蔷薇科等, 草甸主要由禾草类、蒿草(Artemisia)和莎草科(Cyperaceae)等草本植物组成, 夹杂生长针叶树如冷杉(Abies spp.)和云杉(Picea spp.)。

1.2 钻孔特征

本次采样使用俄罗斯手摇钻取得钻孔岩心长度为405 cm, 按 1 cm 间隔分样, 共获得405个样品。岩性描述如下(图 2-A):

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	图 2 贵州草海NT03钻孔岩性柱状图(A)和年代深度框架(B)Fig.2 Lithologic column (A)and age-depth model (B) of Borehole NT03 from Caohai Lake, Guizhou Province

0~50 cm为浅灰色耕作土, 含大量的植物根茎, 受到较多的人类扰动; 50~150 cm为灰黑色黏土, 夹薄层泥炭; 150~220 cm为黑色泥炭, 含腐木和植物碎屑; 220~310 cm为互层的灰色黏土和灰白色黏土, 同样含腐木和植物碎屑; 310~350 cm为黑色黏土, 夹薄层泥炭; 350~380 cm为灰色粉砂质黏土; 380~405 cm为含砾石的浅灰色粉砂质黏土, 砾石大小约为1 cm× 1 cm。

基于钻孔岩性, 在不同深度选取了7个测年样品, 材料主要为含有机质较多的黏土和植物碎屑(表 1), 分别寄送往美国Beta 实验室和西安加速器质谱中心进行加速器质谱放射性碳同位素(AMS ¹⁴C)测年, 并利用IntCal 13数据库(Reimer et al., 2013)将测年结果校正为日历年龄(表 1)。随后, 使用Bacon 2.2软件中内置的Bayesian模型建立钻孔的年龄— 深度模型(Blaauw and Christen, 2011)。

表 1 贵州草海NT03钻孔AMS¹⁴C测年结果 Table1 AMS¹⁴C dating results of Borehole NT03from Caohai Lake, Guizhou Province

结果显示, 钻孔测年结果随深度变老, 未出现倒序现象, NT03钻孔底部年龄为20 915 cal a BP, 平均沉积速率约为1.94 cm/100 yr(图 2-B)。

2 研究方法

本研究涉及的主要代用指标包括色差值(L^*)、烧失量(LOI)、总有机碳(TOC)和全岩有机稳定碳同位素(δ ¹³C_org)等。沉积物颜色是最直观的视觉特征之一, 它包含着丰富的信息, 可在一定程度上反映沉积时的氧化— 还原条件, 是一种重塑古环境的有效参考指标(Nagao and Nakashima, 1992; 吴艳宏和李世杰, 2004; 曾砺锋等, 2018)。色差值测试选用日本Konica Minolta CR400/410型手持色度色差仪, 在中山大学地球科学与工程学院古环境实验室内对岩心表面以1 cm间隔(51.6 yr/样)进行测试, 3次测试取均值, 结果以CIE-L^*a^*b^*色彩空间表示。其中L^*代表明亮度, 变化于黑(0)和白(100)之间, 值越小表示沉积物中有机质含量越高, 沉积物颜色越深; 值越大表示碳酸盐含量越高, 颜色偏亮(吴艳宏和李世杰, 2004)。

沉积物中的有机质和碳酸盐是湖泊沼泽古生产力和区域气候环境特征的地质纪录, 与流域内岩石、气候、水文和生物等要素关系密切, 可指示湖泊沼泽沉积环境的演变历史(刘子亭等, 2006)。烧失量(Loss on Ignition, LOI)是指沉积物中有机质和无机质在一定高温条件下分解后损失的质量百分比, 实验证明550 ℃条件下的烧失量(表示为LOI550)与湖泊沉积物中的有机碳含量关系密切, 因此可用简便高效易得的烧失量值指示沉积物中的有机碳含量(Dean, 1974)。

在NT03钻孔以2 cm间隔(103 yr/样)连续取样, 每个样品重约1.5 g, 共获取207个样品进行烧失量(LOI550)分析, 实验在广东省地质过程与矿产资源探查重点实验室进行, 利用马弗炉对样品进行焚烧, 焚烧时长为4 h(焚烧最佳时长据Heiri et al., 2001)。

沉积物中有机质及其稳定碳同位素的组成受物质来源的影响, 是区域气候环境和水体生产力等因素的综合反应。在NT03钻孔中共获取207个样品进行分析, 取样间隔为2 cm, 平均时间分辨率为103 yr/样。样品经过冻干、挑除明显植物碎屑和研磨后, 加入10% HCl静置反应24 h以去除碳酸盐等无机碳的影响, 随后洗酸至中性, 并冻干。预处理后的样品送至中山大学测试中心进行总有机碳(TOC)和总氮(TN)测试, 使用仪器为Elementar公司生产的Vario EL cube元素分析仪, 分析精度为0.1%; 而稳定碳同位素( $δ^{13} C_{org}$ )测试则在中山大学地球科学与工程学院进行, 使用仪器为Thermo Scientific公司生产的Delta V Advantae 稳定同位素质谱仪, 测试过程中分别加入IAEA-600和GBW04407标样检测, 仪器测量精度优于0.15‰ (VPDB)。

3 测试结果

基于NT03孔的年代框架、岩性和各个指标(色差值L^*、LOI550、TOC、C/N、 $δ^{13} C_{org}$ )的变化特征, 可以把末次冰盛期以来草海地区的沉积环境划分为3个阶段, 各个阶段的指标变化特征如下(图 3, 表2)。

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	图 3 贵州草海NT03钻孔色差值L^、LOI550、TOC、TN、C/N和稳定碳同位素( $δ^{13} C_{org}$ )测试结果Fig.3* Vertical curves of CIE-L^*, LOI550, TOC, TN, C/N ratio and $δ^{13} C_{org}$ of Borehole NT03 from Caohai Lake, Guizhou Province

表 2 贵州草海NT03钻孔环境代用指标数据 Table2 Data of environmental substitute indexes of Borehole NT03 from Caohai Lake, Guizhou Province

沉积环境阶段		L^*	LOI550/%	TOC/%	C/N	$δ^{13} C_{org}$ /‰ , VPDB
Ⅰ		$\frac{20.62 ~ 32.96}{28.47}$	$\frac{3.34 ~ 7.47}{5.31}$	$\frac{3.10 ~ 1.20}{2.08}$	$\frac{18.33 ~ 30.80}{24.96}$	$\frac{- 27.63 ~ - 26.10}{- 26.76}$
Ⅱ	Ⅱ a	$\frac{1.54 ~ 23.83}{17.26}$	$\frac{13.11 ~ 49.50}{27.49}$	$\frac{4.93 ~ 35.51}{14.40}$	$\frac{20.41 ~ 31.86}{25.07}$	$\frac{- 28.35 ~ - 26.22}{- 27.27}$
	Ⅱ b	$\frac{9.02 ~ 37.86}{24.46}$	$\frac{5.89 ~ 27.56}{16.09}$	$\frac{2.42 ~ 26.28}{8.28}$	$\frac{14.23 ~ 30.76}{21.96}$	$\frac{- 28.18 ~ - 26.11}{- 27.26}$
	Ⅱ c	$\frac{6.96 ~ 33.06}{17.73}$	$\frac{30.03 ~ 60.18}{43.64}$	$\frac{6.41 ~ 30.23}{19.86}$	$\frac{16.97 ~ 23.67}{19.21}$	$\frac{- 29.28 ~ - 27.05}{- 27.78}$
Ⅲ		$\frac{5.12 ~ 46.51}{36.19}$	$\frac{5.87 ~ 29.35}{9.58}$	$\frac{0.91 ~ 16.65}{3.12}$	$\frac{5.94 ~ 24.85}{12.90}$	$\frac{- 28.48 ~ - 24.95}{- 26.44}$

注: $\frac{20.62 ~ 32.96}{28.47}$ 表示: $\frac{最小值 ~ 最大值}{平均值}$ 。

表 2 贵州草海NT03钻孔环境代用指标数据 Table2 Data of environmental substitute indexes of Borehole NT03 from Caohai Lake, Guizhou Province

阶段Ⅰ : 405~355 cm(20.9— 15.2 cal ka BP)。此段为钻孔底部沉积, 岩性为灰色粉砂质黏土, 含有磨圆度很差的砾石。在该阶段中, 色差值L^*较高, 平均值约为28.47, 波动区间为20.62~32.96。LOI550的波动区间为3.34%~7.47%(平均值为5.31%)。TOC的平均值较小, 为2.08%, 波动区间为1.20%~3.10%。C/N在18.33~30.80之间波动, 平均值为24.96, 基本大于20。该段内 $δ^{13} C_{org}$ 的值波动幅度较小, 在-27.63‰ ~-26.10‰ 之间波动(平均值为-26.76‰ )。总体来看该阶段除L^*和C/N之外均处于较低水平。

阶段Ⅱ : 355~150 cm(15.2— 4.1 cal ka BP)。此段岩性为灰— 黑色黏土或黑色泥炭。根据各曲线的变化, 可将阶段Ⅱ 进一步划分为IIa、IIb和IIc等3个亚阶段。阶段IIa, 即355~315 cm(15.2~12.0 cal ka BP), 色差值L^*在1.54~23.83之间变化, 且逐步减小, 平均值为17.26, 并在319 cm(12.5 cal ka BP)处出现钻孔最小值1.54; LOI550的值在该亚阶段内稳步增大, 波动范围为13.11%~49.50%, 平均值为27.49%; TOC在330 cm(13.7 cal ka BP)达到全剖面最大值35.51%, 该亚段内的最小值和平均值分别为4.93%和14.40%; C/N的平均值为25.07, 波动区间为20.41~31.86, 在340 cm(14.3 cal ka BP)出现全剖面最大值; $δ^{13} C_{org}$ 的值在-28.35‰ ~-26.22‰ 之间波动, 平均值为-27.27‰ , 自下而上负偏。阶段IIb, 即300~215 cm(10.5— 5.3 cal ka BP)内, 色差值L^*的平均值为24.46, 在9.02~37.86之间变化; LOI550在该亚段内具有先增大后减小的趋势, 在5.89%~27.56%(平均值16.09%)之间波动; TOC在该亚段内也同样呈现先增大后减小的趋势, 平均值为8.28%, 波动区间为2.42%~26.28%; C/N变化幅度较小, 波动区间为14.23~30.76, 自下而上其值逐渐减小, 平均值为21.96; $δ^{13} C_{org}$ 在该亚段内的平均值为-27.26‰ , 波动区间为-28.18‰ ~-26.11‰ , 在280~260 cm(8.2— 7.1 cal ka BP)负偏至最小。阶段IIc, 即215~150 cm(5.3— 4.1 cal ka BP)内, 色差值L^*的平均值显著下降至17.73, 波动区间为6.96~33.06, 该亚段内其值总体处于较低水平; LOI550的平均值在该亚段内迅速上升至43.64%, 且于213 cm(5.3 cal ka BP)处出现全剖面最大值60.18%, 最小值为30.03%; TOC在该亚段内再次上升到高值水平, 平均值为19.86%, 在6.41%~30.23%之间波动; C/N的波动幅度较小, 在16.97~23.67之间波动, 平均值为19.21; $δ^{13} C_{org}$ 的值在该亚段内持续负偏, 波动区间为-29.28‰ ~-27.05‰ (平均值-27.78‰ )。

阶段Ⅲ : 150~6 cm(4.1 cal ka BP以来)。此段岩性主要为灰色黏土, 偶见黑色泥炭夹层。在该段内各项指标均发生明显的增大或减小, 且变化频率和幅度均较大。色差值L^*的平均值为36.19, 波动区间为5.12~46.51, 于84 cm(0.9 cal ka BP)处出现全钻孔最大值46.51。LOI550在该阶段内始终处于低值(平均值为9.58%), 仅在85 cm(1.0 cal ka BP)处出现唯一高值29.35%, 最小值为5.87%。TOC在该段内同样处于低值, 仅在86~82 cm(1.1— 0.9 cal ka BP)之间出现3个相对较大值16.65%、15.35%和13.34%, 其平均值为3.12%, 最小值为0.91%。该段内C/N的平均值显著减小至12.90, 在5.94~24.85之间波动, 于130 cm(3.2 cal ka BP)处出现全钻孔最小值5.94。 $δ^{13} C_{org}$ 的平均值正偏至-26.44‰ 左右, 波动区间为-28.48‰ ~-24.95‰ , 在86 cm(1.1 cal ka BP)处出现全钻孔最大值-24.95‰ 。

总体来看, 在阶段Ⅰ 内, LOI550(有机碳)的值(含量)均接近或达到钻孔最低值, C/N值整体处于较高水平, $δ^{13} C_{org}$ 的值在-26‰ 左右且波动不明显。在阶段Ⅱ 内, 各项指标均出现较大幅度的波动, 同时, 与阶段Ⅰ 相比, 阶段Ⅱ 的 $δ^{13} C_{org}$ 值具有整体负偏的趋势。阶段Ⅲ 内, 各项指标的总体波动趋势仍较一致, 但波动频繁, 显示该阶段沉积环境不稳定。

4 讨论

4.1 有机碳富集与沉积环境

湖泊— 沼泽相沉积物中的有机质含量是反映沉积环境初级生产力的基本指标(Meyers and Lallier-vergé s, 1999)。草海属于流域面积相对较小的湖沼体系, 泥炭沉积的有机质来源主要是生长于湖泊周边浅水湿地及湖泊中的生物。由于草海处于印度季风区, 夏季风增强带来的大气降水可使草海水位上升, 湖沼面积增大。NT03钻孔位于湖沼的边缘区, 根据钻孔分析可以了解草海的水面变化。结果发现, NT03钻孔色差值L^*、LOI550和TOC等的变化趋势一致(图 3), 说明这些指标均能同时反映沉积物中的有机质含量, 从而指示湖泊边缘区的沉积环境, 进而反映区域气候条件。

研究发现, 末次盛冰期阶段(21— 15 cal ka BP), 沉积物中的有机质含量较低, TOC处于低值(< 5%), 沉积物岩性为粉砂质黏土, 含有磨圆度较差的砾石, 推测为冲积相沉积, 可能指示该时期草海水体面积较小, 湖水未淹没到钻孔位置, 与冰期阶段印度季风降雨减弱相吻合。有机碳含量变化曲线清晰显示, 有机碳含量的快速升高始于冰消期的15 ka BP, 其中在对应于B/A事件期的14.8— 12.5 cal ka BP达到峰值, 证明该变化与冰消期冰盖消融和全球回暖有关。西南地区的洞穴石笋(Yuan et al., 2004; Dykoski et al., 2005; Jiang et al., 2014)和湖泊(Yan and Wü nnemann, 2014; 郑茜等, 2014)记录均显示, 印度季风在B/A时期开始显著增强。季风降水增强的结果直接影响草海的湖面高度和水体面积, 使草海湖沼面积快速扩张。由于本钻孔位于草海边缘区, 该地点冰消期沉积物中的有机碳含量增加是湖泊边缘水域扩大导致湿地泥炭堆积和埋藏的结果。此外, 本研究还发现, 晚全新世在5.3~4.1 cal ka BP 是泥炭堆积的第2个峰值, 但在4.1 cal ka BP后, 有机质含量突然快速降低, 沉积物岩性由黑色泥炭变为灰色— 黄色黏土, 指示沉积环境转变为洪冲积相, 该变化的起始点在时间上与4.2 cal ka BP快速变冷事件十分接近, 随后的沉积环境与石笋指示的印度季风减弱有很大的相关性(Dykoski et al., 2005)。

因此, 草海边缘区NT03钻孔中有机碳的富集不仅指示不同时期沉积环境的演变, 同时也反映了印度季风强度变化对水体面积和生态系统的影响。沉积物有机碳在湖泊变浅过程中的湿地沉积泥炭化(沼泽泥炭沉积— 浅湖淤泥沉积— 沼泽泥炭沉积)也存在于亚热带地区其他沉积记录中, 如南岭地区的大湖湿地记录(Zhou et al., 2004; Zhong et al., 2010)也呈现与本钻孔相同的变化模式(图 4-A)。

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图 4 末次盛冰期以来贵州草海NT03钻孔TOC(B. 虚线)、LOI550(B. 实线)、

δ^{13} C_{org}

记录(C)与大湖OM(A. Zhong et al., 2010)、洞穴石笋δ ¹⁸O(D. 实线, 董哥洞, Dykoski et al., 2005; 虚线, 三星洞, Jiang et al., 2014)和区域内其他δ ¹³C 记录(E. 泸沽湖, Zhang et al., 2018; F. 洱海, 张恩楼等, 2017)对比(钻孔NT03位置以及采样位置见图 1-A)Fig.4 Comparison of TOC(B. broken line)、LOI550(B. solid line)、δ ¹³C records(C) of Borehole NT30 from Caohai Lake, Guizhou Province, with Dahu swamp(A. Zhong et al., 2010), speleothem δ ¹⁸O records, (D. solid line, Cave Dongge, Dykoski et al., 2005; D. broken line, Cave Sanxing, Jiang et al., 2014)and other δ ¹³C records(E. Lake Lugu, Zhang et al., 2018; F. Lake Erhai, Zhang et al., 2017)(locations of Borehole NT03 and other samples in Fig.1-A)

上述研究结合岩性变化共同指示该钻孔序列包含了3个沉积环境演变阶段: (1)末次盛冰期晚期(21— 15 cal ka BP)的河流— 冲积相沉积阶段; (2)冰消期至早中全新世(15— 4 cal ka BP)沼泽— 湖泊— 沼泽相沉积阶段; (3)晚全新世(4 cal ka BP至今)洪、冲积相沉积阶段。由于钻孔位置位于草海古湖沼的边缘区, 可以总体反映近2万年以来草海湖沼面积经历的收缩→ 扩张→ 收缩的演变过程, 整个剖面的2个有机碳富集时期对应了全新世大湖期的开始和结束的浅水泥炭沼泽堆积时期。

4.2 有机碳同位素

δ^{13} C_{org}

反映的古环境变化

C/N可用来判断有机质的来源, 一般认为水生浮游藻类的C/N值在4~10之间, 而纤维素含量较高的陆生高等植物的C/N值大于20(Meyers and Lallier-vergé s, 1999)。在草海NT03钻孔中, TOC和T/N变化趋势基本一致, 且C/N值在4 cal ka BP之前大于20(图 3), 指示沉积物中的有机质主要来源于陆生高等植物; 而在4 cal ka BP之后, C/N值一般在10~20之间(图 3), 指示混合的有机质来源。在有机碳同位素 $δ^{13} C_{org}$ 的变化方面, 整个钻孔的 $δ^{13} C_{org}$ 值总体在-30‰ ~-24‰ 之间变化(图 4-C), 与过去在草海东北缘赵家院子剖面的测试值范围基本一致(林瑞芬和卫克勤, 2000)。该数值范围指示本区域自末次盛冰期以来的植被可能均以C3植物(光合作用中同化CO₂的最初产物是三碳化合物— 3-磷酸甘油酸的植物)为主, 即便在LGM变冷气候条件下, C4草本植物(生长过程中从空气中吸收CO₂首先合成苹果酸或天门冬氨酸等含4个碳原子化合物的植物)也无明显扩张。本研究结果与季风区内的其他记录对比发现, 云南泸沽湖(Zhang et al., 2018)最近3万年的同位素值( $δ^{13} C_{PyC}$ )也是在-31‰ ~-24‰ 之间变化, 虽然在末次盛冰期 $δ^{13} C_{PyC}$ 值比草海略为偏正(图 4-E), 但植被面貌均以C3植物为主。此外, 华南亚热带山地的δ ¹³C记录也显示相似的结果(马春梅等, 2008; Li et al., 2013)。本研究认为, 由于C4植物主要分布于太阳辐射量较大的干热地区, 因此在末次冰期寒冷气候条件下, 尽管亚热带山地降雨量有所减少, 但较低的温度和相对充足的湿度等条件限制了C4植物的扩张。

大约始于15 cal ka BP 的冰消期过程中, $δ^{13} C_{org}$ 有负偏的趋势, 该负偏的变化在年代上与邻近的泸沽湖和洱海的碳同位素纪录(张恩楼等, 2017; Zhang et al., 2018)基本一致, 证明了不论是有机碳含量, 还是碳同位素都受到冰消期气候转暖的影响。但YD快速变冷事件虽然在石笋记录(Dykoski et al., 2005; Jiang et al., 2014)中有明显的表现, 但本研究的稳定碳同位素 $δ^{13} C_{org}$ 表现微弱。需要注意的是, 本钻孔的C/N值在4 cal ka BP后快速减小(图 3), 指示有机质来源和沉积环境发生了较大变化, 晚全新世 $δ^{13} C_{org}$ 值快速正偏的现象在其他研究中也有发现(张恩楼等, 2017)。

5 结论

位于贵州草海湿地边缘的南屯NT03钻孔的多指标结果显示, 色度、总有机碳和有机碳同位素等指标反映出草海湿地水体面积和生态系统变化过程, 且与印度季风强弱变化有密切关系。末次盛冰期草海湖沼面积相对较小, 沉积物有机碳含量最低, 此时的 $δ^{13} C_{org}$ 同位素值略微正偏, 说明虽然在一定程度上C4植物有所增加, 但仍指示C3植物为优势植被, 反映了印度季风区在冰期仍保持一定的降雨量, 有利于C3植物的生存。自14.8 calikaiBP开始沉积物有机碳含量快速增大, 反映了草海湖沼的边缘泥炭湿地沼泽相扩大至钻孔位置, 指示了湖泊扩大和降雨量的升高, 在时间上与B/A冰消期暖事件吻合。同时, 冰消期至早全新世 $δ^{13} C_{org}$ 存在负偏现象, 与泸沽湖等邻近地区的碳同位素在冰消期内的变化趋势一致。全新世湖水位最高出现在10.5— 5.3 cal ka BP, 指示了区域全新世最温暖期的年代范围, 这与石笋氧同位素纪录指示的季风增强时段也大体一致。晚全新世大约4 cal ka BP的多指标记录显示本地区沉积环境发生突变, 指示气候条件迅速转为干冷, 时间上与晚全新世季风减弱存在明显对应关系。

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[13]	郑茜, 张虎才, 明庆忠, 常凤琴, 蒙红卫, 张文翔, 刘梦竹, 沈才明. 2014. 泸沽湖记录的西南季风区15000 a BP以来植被与气候变化. 第四纪研究, 34(6): 1314-1326. [Zheng Q, Zhang H C, Ming Q Z, Chang F Q, Meng H W, Zhang W X, Liu M Z, Shen C M. 2014. Vegetational and environmental changes since 15 ka B. P. recorded by Lake Lugu in the Southwest monsoon domain region. Quanternary Sciences, 34(6): 1314-1326] [文内引用:1]
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[18]	Chen F H, Chen X M, Chen J H, Zhou A F, Wu D, Tang L Y, Zhang X J, Huang X Z, Yu J Q. 2014. Holocene vegetation history, precipitation changes and Indian Summer Monsoon evolution documented from sediments of Xingyun Lake, south-west China. Journal of Quaternary Science, 29(7): 661-674. [文内引用:1]
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[21]	Dykoski C A, Edwards R L, Cheng H, Yuan D X, Cai Y J, Zhang M L, Lin Y S, Qing J M, An Z S, Revenaugh J. 2005. A high-resolution, absolute-dated Holocene and Deglacial Asian Monsoon record from Dongge Cave, China. Earth and Planetary Science Letters, 233(1-2): 71-86. [文内引用:3]
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1993

0.0

... 地处中国贵州的草海湿地属于高原湖沼沉积体系,其沉积序列记录了丰富的自晚更新世以来的环境演变信息(陈佩英等,1993 ...

... 但之前关于有机碳同位素的研究存在年代框架精度较低(陈佩英等,1993)或时间跨度较短(朱正杰等,2010)等问题 ...

2008

0.0

韩冰, 欧阳志云, 徐卫华, 肖静, 蒋明康, 王智, 秦卫华. 2008. 中国西南地区物种多样性保护效果. 生态学报, 28(9): 4589-4593.

[Han

, Ouyang Z

, Xu W

, Xiao

, Jiang M

, Wang

, Qin W

. 2008. The effect of protecting species diversity in Southwest China. Acta Ecologica Sinica, 28(9): 4589-4593]

Establishment of nature reserves is one of the best ways to protect speciesbiodiversity. The effect of protecting species was analyzed in this study by selecting 40 important and typical nature reserves in Southwest Chinawith the aim of providing evidence for the management on nature reserves. Main results were as follows: (1)The number of wild animals and plants species protected in reserves increased logarithmically with the increase of nature reserves. By this way the total number of wild vertebrates protected in nature reserves of the Southwest were estimated as 2426, occupying 38.2 percent of total wild vertebrates species in China. (2) Wild higher plants species protected in nature reserves of the Southwest were 20965, which were almost 70 percent of total wild higher plants species in China. (3) It showed that the number of plant and animal species protected in reserves was positively linearly related to the area of reserves when below 1.5 million ha, and almost kept unchanged above that area. This indicates that the habitats of other endemic wild species beyond the species in the existing reserves should be considered in the establishment of new nature reserves. (4) The total number of China′s important species protected in the reserves of Southwest China was also established: wild animals protected were 119, of which 42 were in Class I and 77 were in Class II, taking 46.3% of total national important animal species in China. The wild plants protected were 138, of which 29 in Class I and 109 in Class II, occupying 54.3% of total national important plant species.

通过选取比较重要的40处自然保护区，对我国西南地区自然保护区的物种保护效果进行了研究，以期对自然保护区的规划与管理提供一些依据。研究结果如下：通过回归分析发现，随着自然保护区的增加，受保护的野生动物（植物）物种总数呈现对数增长的趋势，由此得到西南地区受保护的野生脊椎动物物种总数为2426种，为我国野生脊椎动物物种总数6347种的382％；西南地区受保护的野生高等植物物种总数为20965种，是我国野生高等植物物种总数30000多种的近70％。我国西南地区在自然保护区的总面积为150万hm2以下时，受保护的动物（植物）物种总数与自然保护区的总面积呈现显著直线正相关关系，当总面积大于150万hm2时，受保护的动物（植物）物种总数增加不明显，因此要增建扩建自然保护区，应从保护珍稀濒危野生物种的角度考虑。在我国西南地区自然保护区中，得到保护的国家重点保护动物共119种，是国家重点保护动物总数的463％，其中保护的1级保护动物42种，保护比例为43.8％，保护的2级保护动物77种，保护比例为47.8％；得到保护的国家重点保护植物共138种，为国家重点保护植物总数的54.3％，其中保护的1级保护植物29种，保护比例为56.9％，保护的2级保护植物109种，保护比例为53.7％。

... 前人丰富的湖泊多指标古环境研究成果为西南地区的环境变化研究提供了重要认识,但由于受印度季风影响的亚热带地区地形复杂,地势起伏较大,且生物多样性丰富(韩冰等,2008),不同地区的生态系统对于气候变化的响应机制和过程是否一致,需要空间覆盖更密集的古环境记录进行对比研究 ...

1988

0.0

... 根据《贵州植被》(黄威廉等,1988)中的划分,草海地区的植被垂直分带如下: 海拔小于 2400 m为黄棕壤分布区,是常绿阔叶和少量针叶树种分布带,主要的树种有马尾松(Pinus massoniana)、滇黄栎(Cyclobalanopsis delavayi)、滇青冈(Cyclobalanopsis glaucoides)、云南樟(Cinnamomum glanduliferum)、红木荷(Schima wallichii)等 ...

2013

0.0

... 孔凡翠等,2013) ...

2000

0.0

... 之间变化(图 4-C),与过去在草海东北缘赵家院子剖面的测试值范围基本一致(林瑞芬和卫克勤,2000) ...

1987

0.0

... 1 区域概况草海盆地位于贵州省威宁彝族回族苗族自治县境内,地处云贵高原,该盆地受威宁弧形背斜控制,为一山间盆地,处于长江水系和珠江水系分水岭的古老夷平面之上(林树基和郑洪汉,1987) ...

... 湖沼相沉积主要分布于盆地中部草海湖区及附近谷地中,主要由黏土和富有机质泥炭组成,最大厚度可达85 m(林树基和郑洪汉,1987) ...

2006

0.0

... 沉积物中的有机质和碳酸盐是湖泊沼泽古生产力和区域气候环境特征的地质纪录,与流域内岩石、气候、水文和生物等要素关系密切,可指示湖泊沼泽沉积环境的演变历史(刘子亭等,2006) ...

2008

0.0

... ¹³C记录也显示相似的结果(马春梅等,2008 ...

2018

0.0

... 沈吉和肖霞云,2018) ...

2004

0.0

吴艳宏, 李世杰. 2004. 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, 19(5): 789-792.

[Wu Y

, Li S

. 2004. Significance of lake sediment color for short time scale climate variation. Advances in Earth Science, 19(5): 789-792]

Deap-sea sediment-color record from Atlantic has been widely used to reconstruct climate variation on millennial time scales. Can lake sediment color be used to reflect climate change in shorter timescale? In this paper we have discussed it based on statistical correlation between L*, a*, b* (CIE/L*a*b* color system) and some geochemical proxies. L* (brightness) is positive correlated with carbonate content, and higher L* value corresponds to higher carbonate content and cold and dry climate, and vice versa. a* value (red-green color) is correlated with Mg content in sediments. Higher a* value corresponds to higher MgO content in sediments and higher Mg/Ca ratio of sediments which reflect warmer climate. b* value is positively correlated with Fe 3+ content. Higher b* value represents sediments formed in oxidation condition, and b* value can indirectly reflect lake water depth change and efficient moisture change. To sediments of Gourenco Lake, the curve of a* value is mirrored with that of b* which reflects the climatic combination of cold and dry or warm and wet in this area. Based on the significance of lake sediment color in Gourenco Lake, the climate change in this area can be deduced since 1400 AD. Since 1400 AD, climate in this area has undergone several times of fluctuations. The Little Ice Age began from 1430 AD and ended at 1890 AD. Climate change in recent 40 years is coincided with instrument record of nearby meteorological stations. 

Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing 210008, China

在ODP对大西洋海洋沉积物的研究中，色度作为最直观和简便的指标被普遍用于反映千年尺度的气候环境变化。能否用湖泊沉积物色度反映短时间尺度的气候环境变化？利用CIE／L a b表色系，通过青藏高原可可西里苟仁错湖泊沉积物的 L、a和 b值与有关地球化学指标的统计相关关系分析，对湖泊色度指标在短尺度古气候研究中的意义进行了探讨，并据此分析了 1440年以来苟仁错地区的古气候演变。研究表明，L值（亮度）与沉积物碳酸盐含量正相关，L高时，气候冷干，碳酸盐含量较高；反之，气温上升，湿度增加；a值（红-绿彩度）与沉积物中Mg含量相关，高 a值对应于沉积物中高MgO含量和高Mg／Ca比值，反映气温较高；b（黄-蓝彩度）值与三价铁的含量相关，较高的 b值代表了湖泊处于较强的氧化条件下，因此 b值可以用于反映湖水深度变化，反映有效湿度的变化，b值高，湖水浅，氧化作用增强；苟仁错沉积物 a值和 b值曲线镜像对称进一步反映了冷干-暖湿的气候组合特征。根据沉积物的色度意义，判断苟仁错地区自 1430年进入小冰期，至1890年结束。近40年来气候变化与邻近气象站的器测相吻合。

... 吴艳宏和李世杰,2004 ...

... 值越大表示碳酸盐含量越高,颜色偏亮(吴艳宏和李世杰,2004) ...

2018

0.0

曾砺锋, 陈聪, 郑卓, 肖凡, 黄康有, 满美玲, 田俐萍. 2018. 雷州半岛九斗洋干玛珥湖火山机构与第四系空间展布—基于高密度电阻率法勘测和钻孔研究. 热带地理, 38(2): 244-254.

[Zeng L

, Chen

, Zheng

, Xiao

, Huang K

, Man M

, Tian L

. 2018. Electrical resistivity tomography of volcanic crater structure and Quaternary lacustrine sediments of Jiudouyang Maar Paleolake, Leizhou Peninsula. Tropical Geography, 38(2): 244-254]

Maars, formed by phreatomagmatic eruptions, are major concern of volcanology and paleoenvironment research. There are many Quaternary maars located in Leiqiong Volcanic Field, south China, which provide excellent archives for paleoenvironmental reconstructions. To clarify the spatial distribution of Quaternary sediments and volcanic structure of Jiudouyang maar paleolake, Leizhou Peninsula, we conducted electrical resistivity tomography (ERT) imaging surveys in the crater, accompanying with core drilling that was used to verify the resistivity results. Two profiles along the major and minor axis of the crater respectively, comprised of five segments with lengths varying from 900 to 1 200 m, were collected by means of Wenner array with 10 m electrode spacing. They were inverted by using Res2dinv software, and the result allowed imaging the uppermost 150 m strata. The basalt bedrock with higher resistivity (more than 80 Ω?m) is distinct from the upper Quaternary sediments and the interface is approximately flat, revealing that the crater basin has a bowl-like shape rather than a funnel shape. Moreover, magma conduit is characterized by abnormal high resistivity (up to 300 Ω?m), which is surrounded by the underlying Quaternary sediments (e.g., the Zhanjiang Formation or the Beihai Formation). Volcanic structure as above is corresponding with universal model of soft-substrate maars but not hard-substrate maars. In contrast, the upper Quaternary lacustrine sediments are characterized by low resistivity (less than 60 Ω?m) areas where the thickness varies between 25 and 50 m. Based on variations in lithology, the sediments sequence can be divided into five units from top to bottom: Unit 1 (0-6.18 m), reddish yellow clay and fine sand with occasionally irregular gravel (1.96-3.07 m); Unit 2 (6.18-11.70 m), green-greyish clay; Unit 3 (11.70-13.37 m), organic-rich clay with wood fragments and organic detritus; Unit 4 (13.37-38.51 m), green-greyish diatomaceous clay to diatomite, with some varve-like laminae (29.23-31.86 m); Unit 5 (38.51-47.60 m), diatomite laminae with a layer of tephra and scoria (38.51-39.55 m); Unit 6 (47.60-49.49 m), tephra and pyroclastic breccia, overlying the unweathered basalt. Despite of some slight offsets in depth resulted from the limit of spatial resolution of ERT, it shows agreement between the coring stratigraphy and electrical resistivity profiles. For instance, organic-rich clay layer (Unit 3) is corresponding to the lowest values of resistivity result (<5 Ω?m), because of its lower density and higher water content. Overall, we have successfully imaged the volcanic structures and sediment spatial distributions, and testified that electrical resistivity tomography would be an ideal method to provide fundamental information for other researches.

（School of Earth Sciences and Engineering，Sun Yat-sen University，Guangzhou 510275，China）

为查明雷琼火山群中九斗洋干玛珥湖的第四纪地层空间展布,以及埋藏古火山形态,为后续研究提供地质背景资料,采用高效、便捷的高密度电阻率法对九斗洋干玛珥湖湖盆区进行勘测,并结合钻孔岩芯的研究进行验证。得出的主要结论为：1）盆地深部地层最高电阻率可达到300 Ω?m以上,盆地中央基岩以下存在高阻地质体,推测为岩浆通道位置。岩浆经过通道溢出后横向展布,覆于沉积地层上,随后在火山口内形成湖泊,堆积第四纪湖相沉积,其火山机构与玛珥湖型火山一致；2）九斗洋干玛珥湖第四纪松散沉积地层的电阻率通常<60 Ω?m,泥炭层电阻率最低；3）第四纪沉积总厚度为25~50 m,盆地松散沉积的岩浆岩基底总体平整,但尚有波状起伏。研究结果表明,高密度电阻率法结合钻孔验证是研究火山机构形态及火山口湖第四纪沉积空间展布的有效方法。

... 曾砺锋等,2018) ...

2017

0.0

... 印度季风作为亚洲季风的重要组成部分,从热带印度洋携带大量水汽输送至南亚内陆形成季风降水,对区域水文循环和生态系统产生重要影响(Zhang et al ...

... Zhang et al ...

... 印度季风带来的降水与西印度洋海表温度关系密切,并与海陆水文循环存在重要联系(Zhang et al ...

... 大约始于15 cal ka BP 的冰消期过程中, δ13Corg有负偏的趋势,该负偏的变化在年代上与邻近的泸沽湖和洱海的碳同位素纪录(张恩楼等,2017 ...

... 需要注意的是,本钻孔的C/N值在4 cal ka BP后快速减小(图 3),指示有机质来源和沉积环境发生了较大变化,晚全新世 δ13Corg值快速正偏的现象在其他研究中也有发现(张恩楼等,2017) ...

2014

0.0

郑茜, 张虎才, 明庆忠, 常凤琴, 蒙红卫, 张文翔, 刘梦竹, 沈才明. 2014. 泸沽湖记录的西南季风区15000 a BP以来植被与气候变化. 第四纪研究, 34(6): 1314-1326.

[Zheng

, Zhang H

, Ming Q

, Chang F

, Meng H

, Zhang W

, Liu M

, Shen C

. 2014. Vegetational and environmental changes since 15 ka B. P. recorded by Lake Lugu in the Southwest monsoon domain region. Quanternary Sciences, 34(6): 1314-1326]

Lake Lugu, located at the southeastern Tibetan Plateau(27°40'~27°44'N, 100°46'~100°55'E), is the second largest deep plateau-lake in Yunnan-Guizhou Plateau. A 880 cm long core(at 27°40'49″N, 100°48'00″E) taken from 44.5m water depth of the lake shows that its sediments are rich in organic matters with leaf remains but without distinguishable physical features. The age-depth model of the Lake Lugu core is established from 16 AMS 14 C dates. This paper presents pollen assemblages of its upper 474 cm, together with the measurement of the TOC and CaCO 3 to reconstruct past vegetation and environment changes during the last 15000 years. Among the 70 samples analyzed, a total of 81 pollen and spore taxa were identified. Trees were the dominant pollen in the entire profile and the average content of trees was 92.1%, and the maximum value was as high as 97.3%. On average, herb accounts for 7.9% on average. One of the typical features from the pollen diagram identified from the sediments from Lake Lugu is that the content of Pinus spp. is high all through the profile, which averagely can reach about 38.5% ~74.6%. The samples from the top 3 cm contents too much water than sediments, therefore, it's difficult to sample and they were not considered here. Based on the pollen percentages of the major taxa and CONISS results, the pollen record from the Lake Lugu was divided into six main zones:(1)From 15000a B.P. to 12300a B.P., pine forests together with alpine coniferous and broadleaved mixed forests occupied the drainage of Lake Lugu, indicating a cool and humid conditions.(2)It was followed by a warm and dry period marked with a decline of pine forests and an increase of deciduous broadleaved forests from 12300a B.P. to 10300a B.P.(3)During the Early and Middle Holocene(10300~7500a B.P. and 7500~3800a B.P.), high coverage vegetation was dominated by pine forests, together with a few alpine coniferous forests consisting of hemlock, fir and spruce, indicating warmer and wetter conditions than those in 15000~12300a B.P. However, more evergreen oaks occurred in the Middle Holocene, suggesting that climatic conditions were not as humid as in the Early Holocene. (4)Pollen spectra from 3800a B.P. to 3300a B.P. showed a marked decline of pine forests and a distinct expansion of sclerophyllous evergreen oak forests, reflecting a 500-year cool and dry climate event.(5)From 3300a B.P. to the present, pine forests recovered from its shrink of 3800~3300a B.P., but did not reach the Early and Middle Holocene level, evergreen broadleaved Cyclobalanopsis forests and coniferous hemlock-fir-spruce forests frequently occurred in the lake drainage. Past vegetation indicated that temperature and humidity in the Late Holocene were lower than those in the Early and Middle Holocene. Lake environmental changes revealed by TOC and CaCO 3 were consistent with climatic changes reflected by pollen spectra. The TOC contents vary between 3.78% ~13.80% (with average of 8.79%). Low lake levels were generally parallel with cool and dry climatic conditions. TIC content is one of the proxies for water levels. Based on this assumption, it is believed that high lake levels appeared between 13600a B.P. and 3800a B.P., during that period the water level fluctuated with a periodicity of 600~1230a. Overall, pollen, TOC, and CaCO 3 records from Lake Lugu revealed a trend of temperature rise-high temperature-temperature drop, superimposed with a series of cool and dry events.

Key Laboratory of Plateau Lake Ecology and Globe Change, Yunnan Provincial Key Laboratory of Plateau Geography Process and Environment Changes, College of Tourism and Geography Science, Yunnan Normal University, Kunming 650500

泸沽湖是云贵高原第二大深水湖。取自水深44.5m处长度880 cm的连续岩芯显示, 泸沽湖沉积岩芯物理特征变化不明显, 色调单一、物质构成均匀、植物残体(古树叶)丰富。本文对该岩芯上部474 cm进行了孢粉分析和TOC(总有机碳)、CaCO 3 (碳酸钙)百分含量的测定。在16个树叶残体 AMS 14 C 测年基础上建立了岩芯的年代序列。岩芯孢粉组合表明, 在泸沽湖流域, 15000~12300a B.P. 植被以松林为主, 伴有山地针叶阔叶混交林, 指示温凉偏湿的气候条件; 12300~10300a B.P. 的植被以松林减少而落叶阔叶林扩张为特点, 表明当时气候相对偏暖偏干; 在早全新世(10300~7500a B.P.)和中全新世(7500~3800a B.P.), 植被以松林占优势, 伴有铁杉林和云冷杉林, 植被盖度大, 反映温暖湿润的气候条件; 在中全新世常绿栎类偏多, 表明有效湿度不如早全新世; 在3800~3300a B.P., 松林明显减少而硬叶常绿栎林急剧扩张, 指示了一次持续的冷干事件; 在晚全新世(3300a B.P. 至今), 松林有所恢复但未达到早中全新世的水平, 常绿青冈林增加并出现较多的铁杉林和云杉林, 但植被盖度明显降低, 表明晚全新世的气温和湿度比早中全新世均偏低。TOC和CaCO 3 含量反映的湖泊环境和湖面变化与孢粉分析结果有较好的对应, 虽然彼此在年代上存在一定的差异。碳酸盐含量变化显示在13600~3400a B.P. 期间湖水整体较高并形成间断性外流湖。泸沽湖沉积记录不仅揭示了末次冰消期以来升温-高温-降温的变化趋势, 还记录了与Younger Dryas(YD)和约4000a B.P. 的冷事件等相关的气候异常事件。因此, 本研究对于认识我国西南地区现代气候环境变化过程、气候突变事件及植被演化具有重要意义。

... 郑茜等,2014)记录均显示,印度季风在B/A时期开始显著增强 ...

2010

0.0

... 朱正杰等,2010 ...

... 但之前关于有机碳同位素的研究存在年代框架精度较低(陈佩英等,1993)或时间跨度较短(朱正杰等,2010)等问题 ...

2011

0.0

... , 2017),前人对印度季风在不同时间尺度上的演化历史、驱动机制及其生态响应进行了研究(An et al ...

... 研究认为南北半球共同影响印度季风(An et al ...

2011

0.0

... 深度模型(Blaauw and Christen,2011) ...

2015

0.0

... Cai et al ...

2014

0.0

... Chen et al ...

1974

0.0

... 烧失量(Loss on Ignition,LOI)是指沉积物中有机质和无机质在一定高温条件下分解后损失的质量百分比,实验证明550 ℃条件下的烧失量(表示为LOI550)与湖泊沉积物中的有机碳含量关系密切,因此可用简便高效易得的烧失量值指示沉积物中的有机碳含量(Dean,1974) ...

2014

0.0

... Deplazes et al ...

2005

0.0

... Dykoski et al ...

... 2 cal ka BP快速变冷事件十分接近,随后的沉积环境与石笋指示的印度季风减弱有很大的相关性(Dykoski et al ...

... 但YD快速变冷事件虽然在石笋记录(Dykoski et al ...

2001

0.0

... 5 g,共获取207个样品进行烧失量(LOI550)分析,实验在广东省地质过程与矿产资源探查重点实验室进行,利用马弗炉对样品进行焚烧,焚烧时长为4 h(焚烧最佳时长据Heiri et al ...

2014

0.0

... Jiang et al ...

2013

0.0

... Li et al ...

1999

0.0

... 沼泽相沉积物中的有机质含量是反映沉积环境初级生产力的基本指标(Meyers and Lallier-vergé ...

... C/N可用来判断有机质的来源,一般认为水生浮游藻类的C/N值在4~10之间,而纤维素含量较高的陆生高等植物的C/N值大于20(Meyers and Lallier-vergé ...

1992

0.0

... 还原条件,是一种重塑古环境的有效参考指标(Nagao and Nakashima,1992 ...

2013

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... 基于钻孔岩性,在不同深度选取了7个测年样品,材料主要为含有机质较多的黏土和植物碎屑(表 1),分别寄送往美国Beta 实验室和西安加速器质谱中心进行加速器质谱放射性碳同位素(AMS ¹⁴C)测年,并利用IntCal 13数据库(Reimer et al ...

2014

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... , 2014)和湖泊(Yan and Wü ...

2004

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... 西南地区的洞穴石笋(Yuan et al ...

2017

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2018

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... 本研究结果与季风区内的其他记录对比发现,云南泸沽湖(Zhang et al ...

... Zhang et al ...

2010

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... Zhong et al ...

2004

0.0

... 沼泽泥炭沉积)也存在于亚热带地区其他沉积记录中,如南岭地区的大湖湿地记录(Zhou et al ...

2011

0.0

... yunnanensis)为代表的针叶林,以及以常绿、落叶栎为代表的常绿落叶阔叶林,海拔较高处分布有中旱生山地草坡(Zhu et al ...

2014

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... C(Zhu et al ...