IODP 355 Moratorium Proposal: Cenozoic evolution of the Asian Monsoon: tectonic-climate interactions

亚洲季风是当今地球上最引人注目的气候现象之一。几乎三分之二的人生活在受季风影响的区域内，每年降雨的强度和多变性对该区域的繁荣至关重要。了解是什么控制了亚洲季风，以及它在过去是如何变化的，这不仅对科学家，而且对普通民众都很重要。现代季风的强度可能反映了这样一个事实，即HTP是地球上5亿多年来看到的最大的山脉。这种巨大的构造作用力相应地对地球的大气系统产生了特别大的影响。然而，这种拟议的关系是一场旷日持久的辩论的基础。为了确认HTP和季风强度之间的关系，科学家们需要连续的地质序列，这些序列记录了大约5000万年前印度和亚洲板块碰撞以来高原和季风强度相对缓慢的增长。这种记录存在于亚洲周围的海洋中，目前正由国际海洋发现方案(IODP)钻探。与喜马拉雅-青藏高原(HTP)构造演化相关的季风的爆发和加强可能是影响新生代全球气候条件的最重要的过程，但缺乏明确的因果关系证据仍然是地球科学中的一个主要问题。如果不能更好地了解季风形成的时间和方式，就不可能证明气候和构造之间的任何联系。有了这些信息，这样的发展就可以与构造抬升和伸展或其他可能的新生代气候驱动因素相关，也可以不相关。例如，HTP的化学风化和与之相关的季风的启动被援引为吸收大气二氧化碳的机制，表明这种风化是新生代气候系统的组成部分。研究突出了约8 Ma的显著气候变化，而约23 Ma的气候变化代表了季风的加强。另一方面，另一种模型认为，中亚浅海的撤退(Paratthys)是一个关键的边界条件影响，而其他研究人员则认为季风的加强与其中任何一个有关：南中国海的开放，西太平洋暖池的形成或全球变冷。解决这样的古气候问题对于回答有关季风未来对人为变暖的反应的问题至关重要。具体地说，有必要将以下信号去卷积：a)季风对地势和范围基线变化的响应，受隆起和固体地球过程的驱动；b)季风对晚新生代二氧化碳升高和全球变暖的关键时期的响应，例如约3.5Myr的中上新世暖期(MPWP)；约18-15Myr的中中新世气候最佳时期(MMCO)和约48-56Myr的始新世早期。

The Asian Monsoon is one of the most dramatic climatic phenomena on Earth today. Almost two thirds of humanity live within regions influenced by the monsoon and the strength and variability of the annual rains are crucial to the prosperity of the region. Understanding what controls what controls the Asian monsoon and how it has changed in the past is important not only to scientists but also the general population. The intensity of the modern monsoon likely reflects the fact that the HTP is the largest mountain chain seen on Earth for more than 500 million years. This huge tectonic forcing has correspondingly made a particularly large impact on the planet's atmospheric systems. However, this proposed relationship is the basis of a long-running debate. To confirm the relationship between the HTP and the strength of the Monsoon scientists need continuous geological sequences which have recorded the relatively slow growth of the plateau and monsoon strength dating back to the collision of the Indian and Asian plates around 50 millions years ago. Such records exist in the oceans around Asia and are now being drilled by the International Ocean Discovery Programme (IODP). The onset and intensification of the monsoon allied with the tectonic evolution of the Himalayan-Tibetan Plateau (HTP) comprises perhaps the most significant processes affecting global climatic conditions during the Cenozoic, but the lack of explicit evidence for a causative relationships remains a major problem in Earth science. Demonstrating any linkage between climate and tectonics is impossible without a better understanding of when and how the monsoon developed. With this information, such developments can then be correlated, or not, to either tectonic uplift and extension, or other possible Cenozoic climate drivers. As an example, chemical weathering of the HTP and associated initiation of the monsoon has been invoked as a mechanism that draws down atmospheric CO2 , suggesting this weathering to be an integral part of the Cenozoic climate system. Studies have highlighted a significant climate change at ~8 Ma, and at ~23 Ma it has been argued these represent monsoon intensification. On the other hand, alternative models propose the retreat of shallow seas from Central Asia (Paratethys) is a crucial boundary condition influence, while other workers have argued the strengthening of the monsoon is linked to either; opening of the South China Sea, formation of the Western Pacific Warm Pool or global cooling. Resolving such paleoclimatic questions is critical to answer questions over the future response of the Monsoon to anthropogenic warming. Specifically it is necessary to deconvolve the signals of: a) Monsoon response to baseline changes in relief and extent, driven by uplift and solid Earth process from: b) Monsoon response to key periods of elevated CO2 and global warmth during the late Cenozoic, e.g. the Mid-Pliocene Warm Period (MPWP) at ca. 3.5Myr; the Middle Miocene Climatic Optimum (MMCO) at ca. 18-15 Myr and Early Eocene at ca. 48-56 Myr.