Collaborative research: Mio-Pliocene evolution of the Indian summer monsoon recorded in the Bengal Fan

印度季风给印度次大陆和喜马拉雅山带来了水分，滋养了地球上一些最大的河流系统，包括恒河-布拉马普特拉河。这是世界上最大和人口最多的河流流域之一，为大约10亿人提供水。河流将盆地周围的沉积物冲刷到印度洋，在那里它们聚集成一个“巨扇”，一个位于河口外的巨大沉积物，向南一直延伸到印度的南端。这些沉积物保存了该地区数百万年环境变化的痕迹，包括森林和草原的宝贵分子指纹以及印度季风夏季降雨量。这项研究涉及南加州大学和伍兹霍尔海洋研究所的教师、研究生和本科生的合作努力，以及国内和国际合作，以解决与社会相关的气候问题，以及更广泛的地球科学研究。具体来说，本研究利用孟加拉巨型扇中部和南端的沉积物岩心，研究了孟加拉巨型扇在过去1800万年中植被和季风降水变化的性质和原因，以及碳埋藏。研究小组还将利用沉积物中的有机碳含量来计算巨扇掩埋的碳量，这些碳与大气中的二氧化碳隔绝。将被验证的中心假设是，夏季季风的降水强度自开始以来一直在变化，并推动了喜马拉雅碳循环的变化。预计降水变化与：1)中新世中期和上新世早期（二氧化碳分压水平与今天相似）的全球变暖有关；2)中新世—上新世风速增强；3)更新世降温。分析方法包括植物叶蜡的化合物特异性氢同位素分析，当与碳同位素配对时，可以解决水文变化是否驱动了该地区C4植物的扩张。与无机代用物进一步配对将确定侵蚀变化如何影响孟加拉扇的有机碳埋藏。

The Indian monsoon brings moisture to the Indian subcontinent and the Himalayas, feeding some of Earth's largest river systems, including the Ganges-Brahmaputra. This is one of the largest and the most populated river basins in the world, providing water for ~1 billion people. The rivers sweep sediments from around the basin into the Indian Ocean, where they accumulate in a "megafan", a giant deposit beyond the river mouth that extends as far south as the southern tip of India. These sediments preserve traces of millions of years of environmental changes in the region, including valuable molecular fingerprints of forests and grasslands and Indian monsoonal summer rainfall amounts.This research engages the collaborative efforts of faculty, graduate students and undergraduate students at the University of Southern California and Woods Hole Oceanographic Institution, along with national and international collaborations, to address societally-relevant climate, and more broadly earth science, research. Specifically, this research uses sediment cores from the center and the southern end of the Bengal megafan to study the nature and causes of the vegetation and monsoon precipitation changes on land and carbon burial in the Bengal megafan over the last 18 million years. The research team will also use organic carbon contents of the sediments to calculate the amount of carbon buried by the megafan, locked away from the carbon dioxide in the atmosphere. The central hypothesis that will be tested is that the intensity of precipitation in the summer monsoon has varied since initiation and has driven changes in the Himalayan carbon cycle. Precipitation changes are expected to be associated with: 1) global warmth in the mid-Miocene and early Pliocene (when pCO2 levels were similar to today); 2) wind speed intensification in the Mio-Pliocene; and 3) cooling in the Pleistocene. Analytical methods include compound-specific hydrogen isotopic analyses of plant leaf waxes, which when paired with carbon isotopes can resolve whether hydrological changes drove C4 plant expansion in the region. Pairing further with inorganic proxies will establish how erosive changes impacted organic carbon burial in the Bengal Fan.