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水分，为包括恒河-雅鲁藏布江在内的一些地球上最大的河流系统提供水源。这是世界上最大、人口最多的河流流域之一，为约 10 亿人提供水源。这些河流将盆地周围的沉积物扫入印度洋，在那里堆积成“巨型扇”，这是河口以外的一个巨大沉积物，一直向南延伸至印度南端。这些沉积物保存了该地区数百万年来环境变化的痕迹，包括森林和草原以及印度季风夏季降雨量的宝贵分子指纹。这项研究需要南加州大学和伍兹霍尔海洋研究所的教师、研究生和本科生的共同努力，以及国家和国际合作，以解决与社会相关的气候以及更广泛的地球科学研究问题。具体来说，这项研究利用孟加拉巨型扇中心和南端的沉积岩芯来研究过去1800万年来孟加拉巨型扇陆地植被和季风降水变化以及碳埋藏的性质和原因。研究小组还将利用沉积物的有机碳含量来计算巨型风扇埋藏的碳量，这些碳与大气中的二氧化碳隔绝。将要测试的中心假设是，夏季风的降水强度自开始以来一直在变化，并驱动了喜马拉雅碳循环的变化。降水变化预计与以下因素有关：1）中新世中期和上新世早期的全球变暖（当时 pCO2 水平与今天相似）； 2）中新世-上新世风速增强； 3）更新世的冷却。分析方法包括对植物叶蜡进行化合物特异性氢同位素分析，与碳同位素配合使用可以确定水文变化是否推动了该地区 C4 植物的扩张。与无机代理的进一步配对将确定侵蚀变化如何影响孟加拉扇中的有机碳埋藏。

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.