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

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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.