%0 Journal Article
%T PALEOMONSOON EVOLUTION AND HEINRICH EVENTS:EVIDENCE FROM THE LOESS PLATEAU AND THE SOUTH CHINA SEA<br>黄土高原和南海陆架古季风演变的生物记录与Heinrich事件
%A 吕厚远
%A 郭正堂
%A 吴乃琴
%J 第四纪研究
%D 1996
%I 
%X In the recent paleoclimatic studies, the variations in loess magnetic susceptibility and organic contents are used as proxy indicators of Asian summer monsoon strength,and those of the grain-size as the proxy of winter monsoon. The grain size record is dominated with a 0.1Ma period. These led to the interpretation that the climate in Asian monsoon area is controlled largely by the variations in global ice volume.However,this is inconsistent with a strong 20000a period in the loess-paleosol sequences.Thus,the major factor controlling paleoenvironmental changes of the East Asian monsoon zone is still a contentious point. The difficulty arises from the fact that the proxy index previously used for summer monsoon is not the seasonal climatic indicator and it is therefore difficult to distinguish the effect of summon monsoon from that of the winter monsoon.This paper presents results of phytolith research from the Baoji loess section during the last 0.15Ma to address this problem.It has been known that since phytolith assemblage has great advantage in seasonal reconstruction of paleoclimate changes, especially in steppe area where vegetation community is dominated by herbaceous plants, phytolity is incomparably superior to pollen. In dry steppe, phytolith production consists of 60%-90% of the total dry production of vegetation community. As most of the herbaceous plants are annul or seasonal growing plants, the evolution of grassland community in steppe area is generally last for about 10 years or a little more, by which phytolith can be used as the seasonal indication of short-term climatic changes.We have established the regressive relation of phytolith assemblages from 153 surface soil samples of China with the modern climatic parameters and obtained six climatic factor transfer functions for January, July and annual mean temperature and precipitation. Fig 1 shows the reconstructed variations in January, July, annual mean precipitation and annual mean temperature in the Baoji loess section in the last 0.15Ma and the correlation with the grain-size record from the Indian Ocean and the oxygen isotope record from deep sea sediments.It is shown in Fig 1 that variations in annual mean temperature, precipitation and January precipitation are in good agreement with that of the oxygen isotopic record. In contrast, July precipitation shows similar variations to the grain-size curve from the Indian Ocean core Rc27-61, which reflects changes in strength of the indian Ocean monsoon.The essence of monsoon variation is thought to have the following two aspects: 1) astronomic effect, 2) topographical and thermal difference. We take into account that the global ice volume may influence the duration time of summer monsoon on a given area through the effect of winter monsoon at orbital scales, and as a result, controlled the annual climatic pattern of the Loess Plateau. But, it did not change the initial periodicity and amplitude of summer monsoon with the quasi-200
%K Heinrich事件
%K 古季风
%K 南海
%K 生物记录
%K 黄土高原
%U http://www.alljournals.cn/get_abstract_url.aspx?pcid=E62459D214FD64A3C8082E4ED1ABABED5711027BBBDDD35B&cid=621CF755B1A341E5&jid=EA07051745CDC8D89D5F01A3A4CFE6A9&aid=F9264019F9B7E7D78E3812D5DDC44F31&yid=8A15F8B0AA0E5323&vid=7801E6FC5AE9020C&iid=CA4FD0336C81A37A&sid=708DD6B15D2464E8&eid=A04140E723CB732E&journal_id=1001-7410&journal_name=第四纪研究&referenced_num=25&reference_num=9