摘要
桂林地区３个石笋分辨率达１０～１００ａ级的δ１３Ｃ记录表明，全新世时期的古生态可以划分为森林植被由兴盛至退化（气候由暖湿至干凉）的３个旋回。早中期旋回人类活动影响较小，晚期旋回影响大，由于人类持续地对森林的破坏，草类植被得以生长，石漠化增强，石笋的δ１３Ｃ值急速上升以后，很难再回复到全新世中期的水平。δ１３Ｃ值大幅度跳跃式的下降，可以确定末次冰期旋回冰消期的终止点，其时限为１０ ７００ａＢ．Ｐ，与δ１８Ｏ记录完全吻合，也可以与海洋氧同位素以及其它记录进行对比。
In order to obtain high resolution paleoecology information in karst areas, 3 stalagmites were taken from the inner part of the caves in Gtulin area. Their serial number was P11, X1 and F4 with the height of 122cm, 188cm, and 14cm respectively. After the stalagmites were cut open along the axis, the radiocarbon dating samples and the stable carbon isotope samples were taken on the sections from the bottom to the top. The dating approaches AMS14C, β-count 14C, α U-series and TIMS U-series and 210Pb were used. Based on the analysis of oxygen and carbon isotopes, the average resolution of P11, X1 and F4 stalagmite reached 85a, 155a and 11a respectively. Additionally, the formation time of F4 stalagmite was only 500a. The changes of oxygen isotope curves basically kept the same pace with those of carbon isotope curves (except of F4 stalagmite). Moreover, δ-values have a negative relahonship with the annual mean temperature. But only the relation between δ13C values and paleoclimate and paleoecology are discussed in this paper. The results indicate that the Holocene paleoecology in Guilin area might be divided into 3 cycles with the epoches of 10 700- 6 100aB. P., 6 100 - 3 200aB. P. and 3 200a B. P. to the present. The cycles were characterized by the forest ecology changes from flourish to decline and the climate changes from warm-wet to cool-dry. In the early cycle, the paleoecology was intensely impacted by the desertification formed in glacial period. Therefore, the soil and vegetation development should take a long bine. The δ13C values fluctuated around the average value of Holocene Epoch. In the middle cycle, the δ13C value reached the minimum and fluctuated below the average value of Holocene Epoch. This period was an optimum epoch with rich rainfall and warm climate, and the forest developed very well. In the last cycle, human activity was intensified, which became the main cause for the continuous decline of the forest ecology. As a result, the grass vegetation gradually expanded and the rock desertification increasingly spreaded. According to the δ13C values from F4 stalagmite, the δ13C value slowly rose in the early stage of the little ice age (1530- 1790A.D.). During the 95 years, the δ13C quicldy increased by 5.8‰ (PDB). Two causes could be taken into account. On the one hand, the population expanded in the later Qianlong age of the Qing Dynasty and the human activity was violent. On the other hand, because of the little ice age, the C3 plant (forest) was cut for warming and C4 plant (various grasses) spreaded. Until the early of 20th century, the ratio of C3 / C4 rose to some extent at the beginning of the recent warm epoch. Nevertheless, the ratio was difficult to go up furthermore. Even in the global warming period from 1970's to the present, the δ13C values of the stalagmite did not decrease, but increased by about 2%. (PDB). On the basis of the abrupt change of the δ13C values, the end I of the Last Glacial period was at 10 700a B. P., which coincided with the record of δ18O. And the record could be correlated with the isotopic records of the deep sea.
出处
《第四纪研究》
CAS
CSCD
北大核心
2000年第4期351-358,共8页
Quaternary Sciences
基金
国家自然科学基金!(批准号:49632100)
国土资源部重点科技项目!(批准号
9501104)
