宁波-姚江平原新石器遗址记录的全新世中期水涝灾害及古人类响应与适应对策

The risk of catastrophic floods in the densely populated coastal lowlands of eastern China, where 144 m people live within 10 m above current sea level in an area of 182,000 km2, is increasing due to global warming. Major flooding in this region would have potentially devastating consequences for loss of life, property, infrastructure and land. Heating of the west Pacific Ocean is increasing storm surge frequency and intensity, while the rate of sea level rise is accelerating, outpacing deposition rates and leading to long-term vulnerability. The Ningbo-Yaojiang plain has a rich archaeological record of Neolithic cultural development, where catastrophic coastal floods during the middle Holocene are recorded as abrupt cultural transitions or even complete interruptions. This project plans to use both archaeological profiles and palaeo-estuarine sediment cores from a range of locations close to known Neolithic sites to infer linkages between past environmental and cultural change by inferring past coastal salinity, relative sea level change and geomorphologic evolution from 8,000 - 3,000 cal yr BP, and relating these to regional records of archaeological change. We will assess the response of coastal geomorphology to sea level change, including river channel avulsion caused by coastal accretion. We also plan to model the tidal and storm surge extent at different sea levels during the middle Holocene and to estimate the area drowned during short-term periods of extreme high sea level caused by typhoons and astronomical spring tides. We can then interpret the impact of marine transgressions and catastrophic flooding caused by storm surges, extreme high tides or channel avulsion on Neolithic cultures, including partial or complete interruptions in the archaeological record, and apply landscape archaeology (e.g. evidence of drainage systems and flood defences) to examine societal strategies for adapting to past environmental change. Results of this project can help prepare the Shanghai region for future challenges of predicted increases in coastal flooding frequency and extent from both long-term sea level rise and short-term extreme flood events. Knowledge of past societal vulnerability and cultural response can be used to improve future resilience by developing effective strategies for mitigation, management and adaption in an uncertain, but dangerous, future.

全球变暖、海平面加速上升正在加大中国东部沿海平原发生涝灾的风险，尤其是西太平洋的显著升温可能改变台风的频率和强度、海平面上升速率可能超过海岸带沉积速率等。浙江宁波-姚江平原众多新石器遗址的文化间歇层极有可能记录了发生于中全新世的类似灾害。我们计划以宁波鱼山-乌龟山遗址的文化间歇层为切入点，充分结合考古发掘剖面和地质钻孔，重建相对海平面曲线和详细恢复距今约8000-3000年前各典型阶段古地形地貌。揭示研究区地貌对海平面波动的敏感性以及河流改道事件与滨海地貌演变的内在联系，并进行各典型阶段风暴潮模拟，揭示风暴潮可达到的有效海平面高度及淹没范围，重现研究区中全新世海侵、涝灾发生过程与机制。我们还将梳理区内众多遗址文化层与生活遗迹的成因和分布变化，分析其与自然环境演变间的关系，揭示古人的适应手段。上述成果将为中国东部沿海地区应对未来极有可能增加的极端气候/气象事件和海平面上升做出准备。

本项目针对姚江-宁波平原新石器遗址地层中普遍出现的文化间歇层，进行其形成机制分析，以探讨滨海低地平原对气候-海平面波动的敏感性以及新石器古人的响应与适应。研究结果显示，在大约6.3和4.5ka，发生两次快速海平面上升事件，对应了研究区两次大范围的海水入侵和文化层堆积中断的现象。在大约5.8ka也发生小尺度海水入侵，可能对应河姆渡早期和晚期文化层堆积的中断。此外，在多个遗址地层中发现6.0、5.3和4.5ka的极端事件。古地形重建显示中全新世杭州湾的几何形态发生显著变化，其中5.6ka古太湖湾的成陆为良渚文化的高度发展提供了充足的土地和淡水资源。但是古太湖湾的充填也导致杭州湾喇叭口形状的基本形成。据此古地形变化所进行的数值模拟进一步显示，新石器晚期杭州湾湾顶地区的天文潮和风暴潮高潮位显著升高。姚江-宁波平原在中全新世的充填，则导致该区域潮差的减小，因此证实了4.5ka以后的长时间海侵事件由区域、甚至全球海平面上升所致。在海平面上升、潮差增大以及极端事件的共同作用下，良渚文化末期水涝灾害风险明显增大，从而触发了良渚文化的衰变。此外，尽管6.3-6.0ka为海侵期，但是宁波平原部分小山丘前缘形成了盐沼环境，因此吸引了河姆渡古人的定居。河姆渡古人通过改变食物结构（即增加海洋食物来源）以及铺垫盐沼的方式作为他们的生存策略。在良渚文化末期，大榭遗址的先民发展了制盐手工业，以适应海平面上升导致的生存环境改变。