2000年来华南沿海气候与环境变化

CLIMATIC AND ENVIRONMENTAL CHANGES ALONG THE SOUTH CHINA COAST OVER THE PAST 2000 YEARS

通过华南沿海两个钻孔剖面的孢粉分析，并用14种热带、南亚热带木本植物花粉含量之和与5种中、北亚热带和暖温带木本植物花粉含量之和的比值作为冷热变化的温度半定量曲线；利用2000年来古籍、地方志记载的典型热带动、植物分布、兴衰的变化作冷暖变化事件；以华南沿海罕见的降雪记载，特别是对15世纪以来的降雪现象分纬度统计其出现频率，探讨华南的小冰期。据此分析华南沿海2000年来的气候和环境变化。

The South China coast is located in south--subtropical and tropical zone, with small variations in temperature' The objectives of this paper are (1) to establish a semiquantitative curve of temperature variations by using the ratio of hot--favourable and cool--favourable pollens in sediment samples densely collected from the cores;(2) to reconstruct climate events based on historic records of animal and plant migrations and snowfalls in ancient books and local chronicles of the past 2000 years; (3) to discuss The Little Ice Age of South China by statistical analysis on latitudinal distribution of the snowfalls frequency since the 15th century. A general picture of the climatic and environmental changes along the South China coast over the past 2 000 years is given.The sporo--pollen analysis of 34 samples reveals 7 types of pollen assemblages for the core P30 in Jiaotang, Panyu (Fig.1) and 6 types for the core H24 in Huangsha,GuangZhou(Fig.2). In addition to sporo --pollen assemblages and dating--data, the ratio of contents of 14 kinds of tropical and south--subtropical woody plant --pollens to that of 5 kinds of north --subtropical and warm temperate woody plant --pollens is used as a semiquantitative index of temperature variations. A time sequence is established by used 14C --age, the geological boundaries of strata and average sedimentationrate (Fig.3). Fig.3shows that the semiquantitative curves of core P30 and core H24 are rather similar,watch coincide with the sea--level changes renected by the curve of diatom--fossils in core P30' This indicates that high sea--level corresponds to high temperature' These two temperature curves can be compared with the temperature curve of China of the past 5000 years established by Prof. Zhu Kezhen' These comparisons show that such semiquantitative curves are useful for environmental interpretation, and reflect 22stages of climatic fluctuations.The occurrence of tropical animal and plant fossils, such as elephant, peacock,crocodile, coconut, betel palm, gomuti palm, tropical hardwood and jack fruit,which can be only found in south--east Asia and Hainan island now, indicates that some climate stages were hotter than for the present in the South China coastal area.For example, a dark mud layer at a depth of 3 m in Minglo, Nanhai, Guangdong,overlaid by a layer of China Cypress, contains elephant skull and thighbones. According to our study on the Quaternary deposits in the Pearl River Delta (PRD), this dark mud layer was generally formed at 2400 -- 2 100 years B. P., and contains cultural relics of the Western Han dynasty' Accordingly, we may infer that the elephant lived in the 2nd--4th century B.C. Crocodile--bone and pottery were also unearthed from this dark mud layer in Shunde. That reflects a hotter climate in the PRD in the Western Han dynasty than for the present. A sample from core E2 in Gull,Chaozhou, Guangdong with a 14C--age of 2 120I90 years B.P. contains 48.8% of warm --favourable castanopsis --pollens and 12.9% of oak --pollens, the highest value in the core. This reflects a warmer climate in the 2nd century B.C. than for the present.The PRD contains many rotten wood. The accumulation of china Cypress in Hetang,Xinhul with a 14C--age of 2 050±100 years B.P. reflects a colder,weather for the lst century B. C., causing many China Cypress died of frost and were bumed underground. There were snowfall records in Guangdong in A.D. lst century. In the early of the 3rd century, it became hotter, crocodile was found in Guangdong' From the 4th to the 12th century, elephant, peacock, crocodile, parror were found in several sites in South China, and a lot of tropical hardwood and jack frint grew and bore fruit in GuangZhou' In the late of the Song dynasty (13th century) it became cold again.GuangZhou had snowed for three days, with snow thickness of 40cm or so. There was not cold record for the 14 ~ 15th century, coconut fruits were numerous and the climate was rather good in Yulin city (Guangxi). Crocodiles were found in Chaozhou city. That means it was quite hot in this period.