Leaf physiognomy records the Miocene intensification of the South Asia Monsoon
Leaf physiognomy records the Miocene intensification of the South Asia Monsoon
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DOI：
10.1016/j.gloplacha.2020.103365
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发表时间：
2021-01-01
影响因子：
3.9
通讯作者：
Valdes, Paul
中科院分区：
文献类型：
--
作者：
Bhatia, Harshita;Srivastava, Gaurav;Valdes, Paul
来自新近纪陆地和海洋沉积物的气候数据表明，早在中新世就开始了近现代的东亚季风，而模拟和其他陆地代用资料表明，原始东亚季风（EAM）和原始东亚季风的起源要早得多。被子植物的叶子，特别是双叶植物的叶子，由于其叶子结构的关键适应，提供了一个很好的指示当时的气候条件。本文利用气候叶片分析多元程序（CLAMP）结合大气环流模式，解码了化石叶片地貌中固有的低（类似于13-11 Ma）和中（9.5-6.8 Ma） Siwalik气候信号。重建的气候数据表明，中西瓦里克比下西瓦里克更温暖、更湿润，特别是在一年中较冷的部分。下、中斯瓦里克组合的叶片地貌与现代叶片组合难以区分，受当今SAM气候的影响。这表明，在中新世晚期（类似于13-11 Ma）， SAM已经作为一个独立的区域建立起来，并且从叶片适应的角度来看，SAM在此后几乎保持不变。定量季风强度指数表明，中新世晚期（9.5-6.8 Ma）季风强度增强，这一发现被气候模拟所复制。
Our understanding regarding the onset and development of the modern South Asia monsoon (SAM) is still incomplete due to its complex nature and differing views about its relationship with major orographic features such as the Himalaya and Tibetan Plateau. Climate data derived from some terrestrial and marine sediments from the Neogene suggests the onset and intensification of the SAM to a near-modern state occurred during the Miocene, while modelling and other terrestrial proxies point to a much earlier origin for the proto-East Asia monsoon (EAM) and proto-SAM. Angiosperm leaves, particularly dicot leaves, provide a good indication of prevailing climatic conditions as a result of key adaptations in their leaf structure. Here we use Climate Leaf Analysis Multivariate Program (CLAMP) in conjunction with general circulation models to decode the Lower (similar to 13-11 Ma) and Middle (9.5-6.8 Ma) Siwalik climate signal inherent in the physiognomy of fossil leaves. The reconstructed climate data indicates that the Middle Siwalik was warmer and wetter than the Lower Siwalik, particularly in the cooler part the year. The leaf physiognomy of Lower and Middle Siwalik assemblages is indistinguishable to that of the modern leaf assemblages, which are influenced by today's SAM climate. This shows that the SAM was already well established as an independent domain during the late middle Miocene (similar to 13-11 Ma) and has remained nearly the same from the perspective of leaf adaptations since then. A quantitative monsoon intensity index indicates an intensified monsoon during the late Miocene (9.5-6.8 Ma), a finding replicated by climate modelling.