Ann Dunlea

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Over one half of the global population is directly dependent on monsoons for their immediate source of water and unexpected variations in monsoon intensity can mean drought or floods for people, crops, and ecosystems across the world. My research focuses on examining variability of the monsoon systems in the past in the context of other global events to better understand how monsoons drive and respond to changing climate.

I probe the mysteries of past monsoons by piecing together clues left in the marine sediment archive. Monsoonal rains erode the Indian continent and feed the rivers transporting the resulting sediment to the ocean. Using a marine sediment core from the Bay of Bengal drilled during Integrated Ocean Drilling Program Expedition 353, I fingerprint the composition of the marine sediment and match it to the geology of India to deduce where, when, and by how much these monsoonal rains were changing in the past. After pinpointing the region supplying sediment to the marine site, I examine isotopes of plant matter preserved in the sediment to infer changes in the hydrological cycle and vegetation in India, which respond to changes in the monsoon.

My techniques involve both inorganic and organic geochemical proxies. I analyze the major, trace, and rare earth element concentrations of many sediment samples downcore and apply a series of interpretive techniques (ratios, x vs. y, ternary plots) including multivariate statistics (Q-mode factor analysis, constrained least squares multiple linear regression) to identify and quantify changes in sediment provenance over time. Additionally, I seek to differentiate the total flux of sediment deposition from rates of weathering on the continent by comparing the behavior of elements that respond differently to continental weathering while considering the effects of authigenic processes occurring in the seafloor. I also analyze organic proxies such as hydrogen and carbon isotopes of leaf waxes extracted from the sediment, which record the fractionation of these elements caused by changes in the hydrological cycle and plant communities. These proxies complement each other by probing different aspects of the monsoon system in the past.

Beyond the Indian Monsoon, I am also continuing research on the East Asian Monsoon using marine sediment cores drilled during IODP Expedition 346 and plan to further expand the global perspective of my research to include the Australian Monsoon.