Mid-Late Holocene climate change and its impact on the agriculture-pastoralism evolution in the West Liaohe Basin
HE Jin,1, LIU Yan1, TIAN Yanguo2, WANG Ze2, XIAO Xin3, JIANG Feng1, LIU Tao4, SUN Qianli1, CHEN Jing1, LI Maotian1, CHEN Zhongyuan,11. State Key Laboratory of Estuarine and Coastal Research, East China Normal University, Shanghai 200241, China 2. Inner Mongolia Prehistoric Culture Museum, Aohan Banner 024300, Inner Mongolia, China 3. Shanghai Broadband Technology and Application Engineering Research Center, Shanghai 200436, China 4. Faculty of Resources and Environmental Science, Hubei University, Wuhan 430000, China
National Natural Science Foundation of China.41620104004 National Natural Science Foundation of China.41971007
作者简介 About authors 何瑾(1996-), 女, 浙江东阳人, 硕士生, 主要从事古气候变化与人类响应研究。E-mail: hejin_pro@163.com
摘要 气候变化是人类文明演化的重要驱动力之一,中国东北西辽河流域地处季风气候敏感带,早中全新世以来古文化演替频繁,具有研究气候变化与早期农业文明响应的重要价值。本文基于西辽河流域兴隆洼(XLW)剖面高精度年代学框架开展多种气候代用指标分析,重建了中晚全新世以来西辽河流域的气候环境演变历史。结果显示,距今5.0 ka以来研究区经历了冷干—暖湿—冷干的气候演变过程。5.0—3.7 cal. ka BP期间,磁化率、烧失量等指标的低值反映了气候由全新世大暖期向冷干环境的转变,可能与东亚夏季风的衰退有关。该时期红山文化衰退,逐渐被以渔猎和农业并重的小河沿文化所取代,东北地区遗址数量有所减少并出现明显南偏。3.7 cal. ka BP后,磁化率、烧失量等指标的高值指示了夏季风的增强,水热条件的改善促进了旱作农业的发展,为夏家店下层文化的发展提供了有利条件。这一阶段东北地区出现人口大爆发,遗址数量达到峰值。2.8 cal. ka BP后,磁化率与烧失量波动降低,表明夏季风波动频繁,气候逐渐转冷干,水热条件的衰退可能导致了夏家店上层文化时期旱作农业的退化与游牧业的发展,且遗址分布出现南偏。 关键词:夏家店文化;西辽河流域;气候演变;农牧交替;文化演替
Abstract Climate change plays a significant role in the evolution of human civilization. The West Liaohe Basin of northeast (NE) China, an area sensitive to monsoon climate change, has a prolonged history of agriculture-based civilizations, making it an ideal place to study human-landscape interactions in the Holocene. Here, analyses of multi-proxies were applied to a sediment profile (XLW) obtained near the Xinglongwa archaeological site, with a reliable chronology that covered mainly the past 5000 years. The result showed that from 5.0 to 3.7 cal. ka BP, the climate turned cooler/drier as indicated by the low magnetic susceptibility and loss on ignition (LOI), coeval with the decline of the East Asian summer monsoon (EASM). This change in climate condition coincided with the demise of agriculture-based Hongshan Culture, which was later replaced by the Xiaoheyan Culture featured by fishing and gathering livelihood. During this period, the number of Neolithic sites in NE China decreased, with a significant southward migration, possibly related to climate deterioration. After 3.7 cal. ka BP, high values of magnetic susceptibility and LOI indicated enhanced terrestrial input, which may result from the strengthening of EASM under a warming climate condition. This could have promoted the recovery of agriculture and boosted the development of the Lower Xiajiadian Culture, during which a demographic expansion was indicated by a significant increase in site numbers. After 2.8 cal. ka BP, a decreasing trend in magnetic susceptibility and LOI hinted the deterioration of EASM with a cool/dry setting, which might have caused a southward shift of settlements in the Upper Xiajiadian Culture when farming was partially replaced by pastoralism. Keywords:Xiajiadian Culture;West Liaohe Basin;climate change;agriculture-pastoralism alternation;culture evolution
PDF (3861KB)元数据多维度评价相关文章导出EndNote|Ris|Bibtex收藏本文 本文引用格式 何瑾, 刘演, 田彦国, 王泽, 肖鑫, 姜锋, 刘韬, 孙千里, 陈静, 李茂田, 陈中原. 西辽河流域中晚全新世气候环境演变及其对农牧业演替的影响. 地理学报[J], 2021, 76(7): 1618-1633 doi:10.11821/dlxb202107004 HE Jin, LIU Yan, TIAN Yanguo, WANG Ze, XIAO Xin, JIANG Feng, LIU Tao, SUN Qianli, CHEN Jing, LI Maotian, CHEN Zhongyuan. Mid-Late Holocene climate change and its impact on the agriculture-pastoralism evolution in the West Liaohe Basin. Acta Geographica Sinice[J], 2021, 76(7): 1618-1633 doi:10.11821/dlxb202107004
1 引言
气候环境演变与古文化发展的关系是过去全球变化(Past Global Change, PAGES)的重要研究内容,也是国内外研究者关注的热点问题[1,2]。已有研究表明,全新世存在着多种尺度的气候波动[3,4,5];气候变化的不稳定性及其对古文化发展与早期农业活动的影响一直被视为研究的重点。位于中国东北的西辽河流域地处东亚夏季风北缘,是暖温带半湿润气候向中温带半干旱气候的过渡地带,对气候环境的变化十分敏感。相关研究认为,自早全新世以来东亚夏季风显著增强,气候带北移[6,7],东北地区进入全新世大暖期。但不同****对东北地区东亚夏季风强盛时期及其气候特征还存在一些争议[8,9,10,11,12]。部分研究表明在东北地区,早全新世夏季风强度大,降水增加,而到了中全新世夏季风则逐渐减弱,降水减少[8, 13],也有****认为东北地区早全新世夏季风弱,中全新世夏季风强,降水较前期增加[9,10,11]。另有研究表明全新世东亚夏季风存在几次极端减弱事件,例如,Liu等[14]认为8.2 cal. ka BP的冷干事件与季风减弱相关,且持续150 a之久;Donges等[15]基于非线性数据网络分析法研究东亚夏季风变化情况,认为东亚夏季风存在4次极端减弱事件(8.5—8.0 ka BP、5.7—5.4 ka BP、4.1—3.6 ka BP、2.8—2.2 ka BP),且与北半球Bond事件相对应。
西辽河流域是中国史前时期重要的文化区块之一——燕辽文化区,过去众多研究已勾画出其总体文化框架[16,17],按时间序列可以概括为新石器时代的小河西文化(9.0—8.5 ka BP)、兴隆洼文化(8.2—7.2 ka BP)、赵宝沟文化(7.2—6.4 ka BP)、红山文化(6.4—5.0 ka BP),铜石并用时代的小河沿文化(5.0—4.2 ka BP)以及青铜时代的夏家店下层文化(4.0—3.3 ka BP)和夏家店上层文化(3.0—2.5 ka BP)。全新世大暖期优越的水热条件促进了兴隆洼—赵宝沟—红山文化时早期农业的快速发展[18,19],而随后的小河沿文化则表现出相对的衰退迹象。晚全新世以来,由于东亚夏季风逐渐衰退,东北地区气候波动频繁[6],这是否在一定程度上与当时的文化更迭有关?
前人研究认为全新世气候波动和极端气候事件的出现与史前文化的发生、扩张和衰退存在一定的对应关系。例如,夏正楷等研究西拉木伦河阶地发育与史前文化的迁移发现,随着河流的下切与摆动,黄土平原被不断切割,河漫滩与河流阶地逐渐形成,人类活动范围由兴隆洼—赵宝沟时期的黄土平原向红山—小河沿文化时期的黄土台塬、河漫滩地区,再到夏家店文化时期的河流二级阶地转移[20]。索秀芬研究内蒙古文化经济形态的转变发现,全新世晚期(3.5 ka BP)以来内蒙古南部曾多次出现农牧业交替的现象,并认为其交替模式与气候的更迭相一致[21]。Xu等提出东北地区史前人类活动可能受周期性气候变化的影响,约0.5 ka的季风旋回与人类活动的强弱密切相关[22]。然而,过去的部分环境考古学研究仅探究西辽河流域文化景观与生业模式的转变,却缺乏高分辨率的气候学证据。因此,本文选取西辽河上游兴隆洼文化遗址附近自然剖面(XLW)为研究对象,通过高精度年代测定以及磁化率、粒度、烧失量等多种沉积学指标的综合分析,拟建立该地区高分辨率气候环境演变序列,并试图探讨不同的气候条件与人类生业模式转变及古文化兴衰的可能关联。
注:深灰色条带对应暖湿期,浅灰色条带对应冷干期,图8同。 Fig. 5Vertical changes of grain size, magnetic susceptibility, LOI, EM1 and EM2 of XLW profile
对EMA粒度端元分析所得的2个端元作自然频率曲线(图6),结果表明EM1呈双峰模式,峰值粒径分别为8.15 μm和57.77 μm;EM2呈单峰模式,峰值粒径为76.43 μm。2个端元随剖面深度的变化曲线表明,剖面底部315~390 cm段(5.07—3.71 cal. ka BP)EM1总体呈低值,范围在24.3%~82.7%之间;在272~315 cm(3.71—3.27 cal. ka BP)EM1达到剖面峰值,并在295 cm处(3.45 cal. ka BP)达到100%;177~272 cm段(3.27—2.82 cal. ka BP)EM1呈上升趋势,并在177 cm处出现高值(70.1%),此后快速下降;110~177 cm段(2.82—2.51 cal. ka BP)EM1出现低值(18.6%~70.1%)。EM2则呈现出与EM1相反的变化趋势。
Fig. 6Frequency distribution curves of EM1 and EM2 of XLW profile
4.3 磁化率分析
根据低频磁化率的变化趋势可以看出,在350~390 cm段(5.07—4.27 cal. ka BP)低频磁化率呈波动下降趋势(图5);272~350 cm段(4.27—3.27 cal. ka BP)低频磁化率明显增加,其中在272~315 cm段低频磁化率逐渐增大并达到整个剖面的最大峰值(155.17× 10-8 m3/kg);235~272 cm段(3.27—3.11 cal. ka BP)低频磁化率波动平稳;177~235 cm段(3.11—2.82 cal. ka BP)低频磁化率呈现较高值,范围在89.84~117.71×10-8 m3/kg之间;此后在177~110 cm段(2.82—2.51 cal. ka BP)低频磁化率呈降低趋势,并在110~152 cm段(2.68—2.51 cal. ka BP)出现最低值(55.62×10-8 m3/kg),之后逐渐恢复。频率磁化率与低频磁化率曲线的变化趋势具有良好的一致性,波动范围在1.64%~13.38%之间。在300~350 cm段(4.27—3.51 cal. ka BP)频率磁化率波动上升,并在295 cm左右(3.45 cal. ka BP)达到最大值,此后波动下降。140~162 cm段(2.73—2.64 cal. ka BP)频率磁化率出现较大波动,与低频磁化率的小幅上升所不同,该段频率磁化率变幅较大并出现高值(9.61%)。
4.4 烧失量分析
XLW剖面烧失量随深度的变化特征表现为:底部与顶部的烧失量相对较低,中部相对较高,其中烧失量最高值出现在295 cm(3.45 cal. ka BP,5.48%),最低值出现在剖面底部(图5)。在350~390 cm(5.07—4.27 cal. ka BP)烧失量总体低于3%并存在持续波动;272~350 cm 段(4.27—3.27 cal. ka BP)烧失量逐渐增加,并在295 cm达到剖面最大值;177~272 cm段(3.27—2.82 cal. ka BP)烧失量呈现小幅波动增加趋势,变化范围为2.24%~4.10%;此后出现波动下降,烧失量逐渐减小并在162 cm处(2.73 cal. ka BP)出现低值(2.04%);在100~140 cm段(2.64—2.32 cal. ka BP)烧失量平稳增加,峰值达到3.71%,此后逐渐下降。
研究区地处东亚夏季风影响范围的北缘,夏季风的强弱变化会影响季风雨带北进的范围,进而对研究区的气候环境变化产生至关重要的影响。5.0—4.3 cal. ka BP期间,XLW剖面沉积物粒度组分以较粗颗粒、以及低频磁化率与LOI逐渐降低为特征,表明磁性矿物与有机质含量减少,生物初级生产力下降,反映气候环境整体处于大暖期最强盛时期向较为冷干气候的过渡阶段,夏季风逐渐减弱。4.3—3.7 cal. ka BP期间,各指标波动较小且保持相对低值,表明气候趋于冷干。自3.7 cal. ka BP后,沉积物粒径减小,低频磁化率与LOI快速上升,表明该时期生物成壤作用强烈,有机质明显增加,气候温暖湿润,降水较为丰富,处于增温增湿阶段。沉积物粒度端元结果显示,3.7—3.2 cal. ka BP期间,沉积物以水成组分EM1占主导并达到峰值,表明此时河流水动力最强,气候最为湿润。结合频率磁化率的大幅增加可知,在3.7—3.2 cal. ka BP期间气候条件处于快速增温增湿阶段。2.8 cal. ka BP以来,低频磁化率与LOI较前期小幅降低,表明该时期风化成壤作用减弱,生物初级生产力降低,相应的,指示风沙输入组分的EM2出现高值,指示该阶段风沙活动较前期增强,气候较为干旱且气候条件较前一阶段衰退。其中,在2.72—2.64 cal. ka BP阶段,频率磁化率快速上升并出现高值,可能记录了该时期一次短暂的气候突变现象,反映气候环境出现短暂的暖湿化,这一结论也在LOI变化趋势上得到印证。总体上,XLW剖面沉积物反映了研究区5000年以来气候趋冷干—回暖增湿—再趋冷干的变化特征[46]。
前人对东北地区的孢粉研究结果表明[26, 47-48],4.5 cal. ka BP前后喜暖植被逐渐被喜冷植被代替,反映了气候趋冷的特征,这可能与东北地区夏季风的减弱有关(图8e)。Guo等[50]对东北沙漠地区沙丘的研究表明,约5.0—4.0 cal. ka BP时沙丘的固定性下降,流动性增加,同时沙漠地区的湖泊水位在6.0—4.0 cal. ka BP逐渐下降,在4.3 cal. ka BP时达到最低。这些现象都表明在这一时期东北地区经历了大范围的气候恶化过程。
注:a1为本文低频磁化率;a2为本文烧失量;b1为岱海地区孢粉拟合的年平均降水量;b2为岱海地区孢粉拟合的年平均气温;c1为四海龙湾玛珥湖最暖月平均温度, c2为四海龙湾玛珥湖年平均降水量;d1为公海湖木本植物孢粉;d2为公海湖磁化率;e为九仙洞δ18O[46];f为东北地区遗址数量与部分遗址出土粟黍比例。 Fig. 8Climate changes inferred from XLW profile versus other proxies from Northeast China
自4.0 cal. ka BP以来,在中国北方许多地区都出现了气候回暖现象。对岱海地区的研究表明,在4.0—3.5 cal. ka BP期间,该地区气候环境有所改善,处于暖湿环境[48,49](图8b)。对比岱海地区气候曲线与本文结果可以发现,两者在气候变化趋势上具有良好的一致性,但在同步性上存在差异,岱海地区暖期峰值出现的时间较西辽河流域更早,这可能是受到指标对气候敏感性差异的影响。Stebich等[50]根据四海龙湾玛珥湖孢粉重建气候的结果表明,在4.0 cal. ka BP出现了全新世降水量的最大值,气候条件最为湿润(图8c),但对比该地区气温降水变化过程与本文结果可知,该地区中全新世以来的气候环境波动较小,这可能与该地区自中全新世以来一直处于夏季风影响区有关,使得其对夏季风波动的敏感性较西辽河流域及岱海地区弱。
3.0 cal. ka BP以来北方地区草原植被出现扩张,木本植物则减少甚至消失,在大兴安岭地区出现了暖温型植被向寒温型植被的过渡[6, 79]。Xiao等[10]对达里湖的研究结果表明,在3.45 cal. ka BP后达里湖曾出现3次明显的低湖面(3.15—2.65 cal. ka BP、1.65—1.15 cal. ka BP、0.55—0.20 cal. ka BP),指示气候环境出现变干的趋势。与之相近的公海湖也在3.3 cal. ka BP后出现木本植物孢粉含量与磁化率的减小,并在2.7 cal. ka BP前后出现低值,指示东亚夏季风的快速衰退过程[11, 52]。而该地区上述指标在5.0—3.0 cal. ka BP期间并未出现较大波动,与本文结果存在差异,这可能与这一时期夏季风的推进范围有关。
5.3 中晚全新世西辽河流域旱作农业与人类活动分布对气候环境演变的响应
已有研究表明,西辽河地区可能是中国旱作农业起源的重要区域[58]。早在8.5 ka BP的小河西文化时期,先民已开始采集和驯化粟类植物作为粮食的来源[57]。到红山文化时期(6.4—5.0 ka BP)耜耕农业达到顶峰,并出现了原始农业文化的第一次繁荣[58]。但在全新世中晚期,由于气候条件的限制及牧业文化的传播,该地区开始出现畜牧业与农业交错盛行的景观。为探究西辽河流域农牧业演替,本文整理了典型遗址中粟黍作物比例、出土农具及动物骨骼数量与类型,以此作为判别生业模式及人类生活环境的依据。黍是由野生狗尾草驯化而成的作物,喜暖抗旱,在干旱的气候和贫瘠的土壤环境下,黍较粟或其它农作物更易栽培,因此其比例上升可能指示着气候的干旱化[59,60,61]。在以农业为主导的生业模式下,出土的农具及炭化作物种子较畜牧业时期偏多,而马作为畜牧业的典型特征,其骨骼数量则较畜牧业时期偏少甚至消失。此外,本文整理了东北地区新石器至青铜时代遗址分布状况,以遗址数量反映人口数量[62],探究该时期人类活动对气候环境的响应。
从XLW剖面恢复的古气候记录可知,红山文化晚期(5.0 cal. ka BP)正处于全新世大暖期向冷干气候的过渡阶段,其衰落可能与水热条件的恶化有关。该时期用于采集收割的农具的减少指示了农业比重的下降、耜耕农业鼎盛时期的结束以及生业模式的转变,进入到以渔猎兼顾农业为生的小河沿文化时期[63,64]。而由于这一转变难以支撑众多人口的生存,就可能使得人类社会矛盾激增,导致人口的相对减少和文化的更替[65,66]。该时期西辽河流域北部受夏季风影响较小,水热条件已不再适合农业的发展,因此小河沿文化仅在南部地区保持低密度的聚落分布[20, 26, 65],且东北地区整体的聚落分布密度均有所减小,范围较前期向南移动(图9a、9b)。
本文基于对西辽河流域兴隆洼(XLW)剖面高精度年代学与高分辨率气候代用指标的分析,重建了东北西辽河流域5.0 cal. ka BP以来的高分辨率气候环境演变过程,并探讨了其对该地区农牧业交替与古文化发展的影响,主要结论如下:
(1)XLW剖面粒度、EMA、磁化率和LOI分析结果表明,5.0 cal. ka BP以来西辽河流域经历了趋冷—转暖湿—冷干的气候波动过程,这与该地区东亚夏季风的强弱变化基本吻合,反映在中晚全新世研究区主要受东亚夏季风波动的控制。
(2)与气候演变过程相对应,西辽河地区的文化演替也出现了衰退—兴盛—衰退的变化过程。5.0 cal. ka BP以来红山文化到小河沿文化时期的文化衰落过程与夏季风的衰退阶段相对应;3.7 cal. ka BP后气候条件的改善可能促进了夏家店下层文化时期旱作锄耕农业的发展,且聚落数量空前增加;2.8 cal. ka BP后随着气候趋于冷干,西辽河北部地区已不再适合单一旱作农业的发展,夏家店下层文化逐渐走向衰落,而代之以半农半牧的夏家店上层文化。
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