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

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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.