深海氧同位素第3阶段时期东亚季风区大气湍流特征

CHARACTERISTICS OF ATMOSPHERIC TURBULENCE IN THE EASTERN ASIAN MONSOON AREA DURING MIS 3

深海氧同位素第 3阶段是末次冰期中的一段特殊时期 ,与全新世存在一定的相似性。为了深入分析深海氧同位素第 3阶段时期的大气环境特征 ,本文利用黄土粒度的多组分特征 ,根据流体力学原理 ,指出其动力学原因是粉尘在搬运过程中风力、湍流和颗粒重力共同作用下形成的分选结果 ;黄土 -古土壤粒度分布中的粗、中粒组分中值粒径近似反映了源区起尘时和沉降区降尘时近地表大气湍流强度的变化。对渭南地区黄土剖面的分析发现 ,末次冰期深海氧同位素第 3阶段以来在中国黄土区存在大致以 4千年为周期交替出现的强湍流期与弱湍流期 ,强湍流期对应于降温事件 ,如Heinrich事件 ,并存在着 3种源区环境控制的不同大气湍流类型 ;在深海氧同位素第 3阶段粉尘源区和沉降区都存在两种不同大气环境类型在时间上的频繁同步交替 ,具有高度的不稳定性和周期性波动特点 ,与末次冰盛期的大气环流模式可能相似 ,而与全新世不同 ;同时在该时期的强湍流降温期源区进退较明显、沉降区环境稳定 ,而弱湍流期源区较稳定、沉降区大气环境变化较大。

The MIS 3 is a special period of the last glacial period and similar to the environment of Holocene on some ways. The multimodal analysis of the grain size distribution of loess can be used to reveal the atmospheric environment during the MIS 3. The multimodal grain size distribution of suspended dust has resulted from the interaction among wind, atmospheric turbulence and the gravity of dust grains along the dust transportation path. The median grain size of the coarse grained composition and the moderate grained composition approximately represents the atmospheric turbulence strength during the dust entrainment period in dust source areas and during the dust deposition period in the dust deposition area. According to the study of the Yangguo loess-paleosol section of Weinan, Shaanxi Province, it has been found that there was an about 4ka cycle alternation of strong turbulence and weak turbulence in China's loess area during MIS 3. Strong turbulence periods are corresponding to cooling events, such as Heinrich event. There are also three patterns of atmospheric turbulence dominated by the environment of dust source areas to be found. During MIS 3, the strong turbulence period and the weak turbulence period occur alternatively in dust deposition area and dust source areas, meaning the instability and periodicity of climatic change, a atmospheric circulation pattern similar to that of LGM but different from that of Holocene. In the strong turbulence periods of MIS 3, the dust source areas varied obviously and the environment of the dust deposition areas was stable. In the weak turbulence periods of MIS 3, the dust source areas varied slightly and the environment of the dust deposition areas was much varying.