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

Mid-Late Holocene climate change and its impact on the agriculture-pastoralism evolution in the West Liaohe Basin

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。

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 humanlandscape 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.