Collaborative Research: Indian Summer Monsoon Variability Reconstructed from Tibetan Lake Sediments

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The Indian Summer Monsoon directly impacts over one billion people, but very little is known about how variable it can be -- whether large increases or decreases in the amount of rainfall from year to year are normal or not. This research will investigate the variability of the monsoon by sampling bottom sediments from four lakes high in the southeastern Tibetan Plateau, which are believed to hold a record stretching back well over 6000 years into the past. Understanding the range of variability will help to improve climate models that are used to simulate the region's response to a range of abrupt and long term changes in temperature, wind circulation patterns, and moisture sources. In addition, understanding the past climate conditions of the region will allow a better understanding of the regional plant and animal populations and interactions, as well as changes in the human cultures of the area. This work will strengthen international scientific relationships between U.S. and Chinese scientific institutions, scientists, and students. Support will be provided for two earlier career scientists, a Ph.D. student and undergraduate students. The research team will collaborate with the Center for Earth and Environmental Sciences in Indiana to develop a new outreach module for 4th to 9th graders that will raise the awareness of issues surrounding water resources locally in Indianapolis, IN, and the United States as well as in the monsoon region.This research will investigate Indian summer monsoon variability during the Holocene with decadally resolved sediment records from four alpine lakes on the southeastern Tibetan Plateau. The proposed research builds on previous NSF-supported work in the Nyainqentanglha Mountains, which are a major center of action in the summer monsoon system and a primary gateway for moisture entering the Tibetan Plateau. Results from previous work demonstrate that lakes in the region contain Holocene-length sediment archives which can be dated with radiometric techniques. These lakes also have decadal sedimentation rates and contain a diverse range of climate proxies that capture both local and synoptic monsoon variability. The team will reconstruct local monsoon variability with physical sedimentology and geochemistry, and synoptic variability with hydrogen isotope measurements on terrestrial leaf waxes. The results will be synthesized with paleoclimate records from the Tibetan Plateau and surrounding region, as well as with records from key regions in the global climate system, like the tropical Pacific and the North Atlantic, to address three central questions: (i) How did Indian Summer Monsoon rainfall vary on decadal timescales during the Holocene? (ii) Is there evidence for an Indian Summer Monsoon response to changing global climate boundary conditions during the middle Holocene at ~5300 years before present? (iii) Did the Medieval Climate Anomaly and Little Ice Age discernibly influence Indian Summer Monsoon precipitation?