NSFGEO-NERC Solving the enigma of the Miocene South Asian monsoon conundrum. An analog to our future

南亚季风的演化表现为岩石圈（青藏高原隆升）、大气（季风环流）、水圈（水循环）和生物圈（陆地生态演化- c4 -草地扩张和海洋生产力）的多圈相互作用。因此，南亚季风研究直接关系到令人信服的高优先级科学问题，如[2020-2030年美国国家科学基金会地球科学展望：地球时间（2020）]中所确定的，包括问题6（地形变化的原因和后果是什么？）问题8（关于气候系统的动力学，地球的过去揭示了什么？）问题9（地球的水循环是如何变化的？）和问题10（生物地球化学循环是如何演变的？）（美国国家科学院和医学院，2020）。因此，南亚季风的研究是地球系统科学研究的典范。由于多球相互作用的性质，南亚季风具有多面性。其特点是季节性降水明显，与硅酸盐岩石的化学风化和碳掩埋效率相关性高，年际反转风场，海洋冷却，生物水花，氧最小带扩大（例如，Betzler et al., 2017; France-Lanord et al., 2016; Pandey et al., 2016）。几十年来，人们一直致力于描绘南亚季风的这些特征；研究结果的累积彻底改变了我们对南亚季风的认识，从不同的角度提供了长期的演化历史序列来联系上述现象。然而，由于南亚季风的多面性，一个重要的问题出现了，这反映了对季风强度的不同观测和矛盾解释。来自海洋和陆地记录的替代研究对南亚季风给出了截然相反的观点：北印度洋的物理、化学和生物特征记录表明，季风引起的上升流在大约13 Ma至8 Ma之间得到了加强。上升流的增强表现为海表温度的快速降温、冷栖有孔虫—球状虫的急剧增加和氧最小带的扩大；而陆地记录显示，季风降水减弱，气候变干，促使c4 -草地扩张，化学风化作用在同一时间间隔内失效。我们组织了一个美英团队（来自4个研究所的6名pi）。我们建议采用有机地球化学代理研究和数值模拟研究相结合的综合方法。我们的目标是重建中新世中期以来南亚季风的长期历史，以表征反映化学和物理条件变化的区域降水模式、海洋生产和海洋环流模式。然后，我们将在数值模拟的背景下建立和描绘青藏高原隆升、季风环流演变和海洋生产之间的联系。

The evolution of the South Asian Monsoon represents the multi-sphere interactions that involve lithosphere (the uplift of Tibetan Plateau), atmosphere (monsoonal circulations), hydrosphere (hydrological cycle), and biosphere (e.g., terrestrial ecology evolution - C4-grassland expansion and ocean productivity). Therefore, the South Asian Monsoon research is directly related to the compelling, high-priority science questions, as identified in [A Vision for NSF Earth Sciences 2020-2030: Earth in Time (2020)], including Question 6 (What are the causes and consequences of topographic change?) Question 8 (What does Earth's past reveal about the dynamics of the climate system?) Question 9 (How is Earth's water cycle changing?) and Question 10 (How do biogeochemical cycles evolve?) (National Academies of Sciences and Medicine, 2020). Hence the study of the South Asian monsoon is exemplary in Earth System Science research.Because of the nature of multi-sphere interactions, the South Asian Monsoon is manifest with multiple facets. It is characterized by the marked seasonal precipitation, high relevance to chemical weathering of silicate rocks and the efficiency of carbon burial, interannual reversal wind fields, ocean cooling, biogenic bloom, and expansion of oxygen minimum zone (e.g., Betzler et al., 2017; France-Lanord et al., 2016; Pandey et al., 2016). Decades of efforts have focused on characterizing those features of South Asian Monsoon; the accumulation of results has revolutionized our knowledge of South Asian Monsoon by offering long-term time series of evolutionary history from different perspectives to link the above phenomenon. However, due to the nature of multiple facets of the South Asian Monsoon, a vital issue arose, which reflects on the divergent observations and contradictory interpretations of the monsoon strength. Proxy studies from the ocean and terrestrial records give very opposite views on the South Asian monsoon: records of physical, chemical, and biological features of the North Indian Ocean reveal that the monsoon-induced upwelling has been strengthened between ca. 13 Ma and 8 Ma. The strengthening of upwelling is characterized by the rapid cooling of sea surface temperatures, the spike increases of cold water-dwelling foraminifera - the global bulloides, and the expansion of oxygen minimum zone; while terrestrial records reveal that the monsoonal precipitation became weaker, the climate became drier that drove the C4-grassland expansion, and chemical weathering lost its efficiency during the similar time interval.We organized a US-UK team (with six PIs from four institutes). We proposed to use an integrated approach that combines the strength of organic geochemistry proxy and numerical modeling studies. We aim to reconstruct a long-term history of the South Asian monsoon since the mid-Miocene to characterize the regional precipitation pattern, the ocean production, and ocean circulation patterns reflecting changes in chemical and physical conditions. We will then establish and delineate the linkages between the uplift of the Tibetan Plateau, the evolution of monsoonal circulation, and ocean production in the context of numerical modeling simulations.