开封市西郊地层“崇祯大旱”事件的孢粉记录

根据开封市西郊9 m岩芯样品的孢粉分析,结合AMS¹⁴C测年、粒度分析和历史文献,揭示区域植被对“崇祯大旱”事件的响应。结果表明,岩芯深度0~1.8 m为20世纪中叶的黄河灌淤层和近期堆垫层,1.8~4 m和4~7.8 m分别为1841年和1642-1644年的黄泛沉积;岩芯存在7.8~9 m、5~7.8 m、2~5 m和0~2 m等4个孢粉带,其中5~7.8 m的孢粉带记录了明末“崇祯大旱”事件。该层段下段（6.7~7.8 m）为黄泛早期沉积物,木本植物花粉减少至整个岩芯的最低值,而藜科花粉比例显著升高并占据绝对优势,同时还伴随有旱生植物白刺属和麻黄属花粉出现,蒲公英属和菊科等耐旱植物花粉含量也相对较高,指示一次干旱事件;上段（5~6.7 m）为黄泛后期沉积物,木本植物尤其是松属花粉含量较高,而藜科等旱生植物花粉相对较少,可能是由于松属等木本植物花粉悬浮能力强而被洪水携带至下游,在水流缓慢或近于滞流时沉积,再加上洪水过后黄泛地面接受当地源、区域源和区域外源花粉的缘故。

A study of the Chong Zhen Drought event from pollen records in the western suburbs of Kaifeng city,China

Close and complicated correlations between climate change and historical social events have been found in recent research, and environmental change functions as an important factor for the rise and fall of human civilization. Although it is unlikely for environmental change today to produce the same impacts as those that happened in the past because of social development, historical case studies of climate change impacts and the resulting social responses can provide analogies for better understanding the impacts of current and future climate change. A 9-m long core was obtained from the western suburbs of Kaifeng City, Henan Province. Detailed pollen analysis, along with AMS¹⁴C dating, grain size and historical documents revealed an extreme drought event in the Late Ming Dynasty (AD 1637-1643) in North China. Sediments below the surface of 0-1.8 m interval of the core are the Yellow River warping layer in the mid-20th century and the recent accumulation layer. In the years AD 1642-1644 and AD 1841, the Yellow River flood sediments deposited below the surface of 4-7.8 m interval and 1.8-4 m interval respectively. There are four pollen zones of 7.8-9 m, 5-7.8 m, 2-5 m and 0-2 m. Hence, the pollen of Kaifeng core is composed of local pollen, regional pollen and extra-regional pollen, most of which come from regional pollen. During the periods of 1440-1450 the weather became dry and during the periods of 1450-1490, the degree of drought ranked only second to the Late Ming Dynasty in North China. It turns out that the 5-7.8 m interval’s palynological assemblage proved the Chongzhen Drought event. The extreme drought event had a devastating effect not only on hydrology and agriculture, but also on society and economy. During the time when the 6.7-7.8 m interval was deposited, the percentage of arboreal pollen dramatically decreased, while Chenopodiaceae pollen increased remarkably, and the percentage of Taraxacum and Asteraceae also increased, drought indicator species such as Nitraria and Ephedra pollen appeared during this period. The percentage of arboreal pollen increased, however, particularly that of Pinus pollen when the 5-6.7 m interval was deposited. Probably because the decrease of vegetation coverage and increase of precipitation variability in the middle reaches of the Yellow River during the drought, which led to more pollen of the top soils into the Yellow River and transport with water. Large arboreal pollen were carried by the flood to the downstream due to suspension ability and deposited in the water slowly or nearly stagnation. In addition, the surface of the Yellow River flooding sedimentary would also accept local pollen, regional pollen and extra-regional pollen, especially Pinus pollen under the influence of the wind. We only have one age data in this study due to the lack of suitable dating materials for accurate radiometric dating, however, this may reduce the accuracy of the study. Moreover, we confirmed the Chongzhen Drought event based on pollen analysis but did not analyze the reasons.