晚新生代亚洲干旱气候发展与全球变冷联系的风尘沉积证据

AEOLIAN DUST RECORDS INDICATE THE LINKAGE OF GLOBAL COOLING AND ASIAN DRYING IN LATE CENOZOIC

在干旱气候背景下常常有风尘物质的释放和传输,风尘沉积被认为是干旱环境变化良好的地质记录。在亚洲中部和中国北方,大面积的干旱区被沙漠戈壁覆盖,这些地区是粉尘物质的重要源地,释放的风尘物质影响局地和区域环境,并通过参与生物地球化学循环等影响更大空间尺度的气候变化。因此,亚洲中部干旱气候的形成和演化以及发展趋势一直受到重视。长期以来,关于晚新生代亚洲中部干旱气候发展的驱动机制至少有两种解释:一是青藏高原的隆升控制着亚洲中部的干旱化过程,随着高原的阶段性隆升亚洲干旱气候逐步增强;二是晚新生代全球变冷直接驱动着亚洲变干,全球变冷是主导因素。中国黄土高原及其周边地区堆积的黄土-红粘土序列是指示亚洲干旱化过程良好的地质记录,通过对新获得的风尘堆积记录的分析,发现在晚新生代中国风尘堆积的时空演化与全球变冷有较好的对应,全球变冷可以促使亚洲中部干旱气候发展并加强粉尘活动,而青藏高原隆升的幅度和时间还不清楚,进而认为是全球变冷而不是青藏高原隆升直接驱动亚洲内陆的阶段性变干。基于这些结果,我们认为以前关于青藏高原隆升影响全球气候的结论可能高估了青藏高原在地球环境演化中的作用,关于高原隆升直接驱动亚洲干旱化的结论还需要检验。

It is suggested that the uplift of the Qinghai-Xizang（Tibetan）Plateau has been a dominant driver of climate drying in Central Asia during Late Cenozoic. Global cooling has also been considered to have forced the stepwise drying and the development of aeolian deposit system in central and Eastern Asia. Which one, the Tibetan tectonic uplift or the global cooling, is the first-order driver to control Asian drying and the consequent aeolian silt expansion is still in controversy. In this paper,we examined new data of the aeolian silt deposit,which is a good indicator of Asian drying during Late Cenozoic, to qualitatively reconstruct Asian drying history. We compared the time series of Asian drying with the time series of global cooling and the possible model of Tibetan uplift in the past 24 ~ 22 million years. Our analysis presents a strong linkage of the global cooling and the Asian drying at tectonic-orbital time scale. In addition, as the timing and amplitude of Tibetan growth during the Late Cenozoic have not been precisely understood, most previous conclusions on the relationship between Tibetan uplift and the Asian drying in Late Cenozoic should be reexamined. The good correlation of the increasing and expansion of the Asian dust, which are indicators of aridification in Central and Eastern Asia, and the global cooling indicates that the global cooling is probably the main driver of the drying in interior Asia in Late Cenozoic, through reorganization of atmospheric circulation and ocean current flow.