Lake sediment records of Indian summer monsoon variability during the Medieval Climate Anomaly and Little Ice: Support for a late Holocene pluvial event on the southeastern Tibetan Plateau

Broxton W Bird, Indiana University Indianapolis, Earth and Environmental Sciences, Indianapolis, United States, Pratigya J Polissar, Lamont-Doherty Earth Observatory, Palisades, United States, Yanbin Lei, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing, China, Lonnie G Thompson, Ohio State University Main Campus, School of Earth Sciences, Columbus, OH, United States, Tandong Yao, ITP Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing, China, Bruce Finney, Idaho State University, Department of Geosciences, Pocatello, United States, Daniel Bain, University of Pittsburgh Pittsburgh Campus, Department of Geology and Environmental Science, Pittsburgh, United States, David P Pompeani, University of Pittsburgh Pittsburgh Campus, Pittsburgh, PA, United States and Byron A Steinman, University of Minnesota Duluth, Earth and Environmental Sciences and Large Lakes Observatory, Duluth, United States
Abstract:
Paleoclimate records from the Third Pole provide a mixed view of Indian summer monsoon (ISM) variability during the Medieval Climate Anomaly (MCA; 800-1000 cal yr B.P.) and Little Ice Age (LIA; 150-550 cal yr B.P.). While some records suggest precipitation increased during the MCA and declined during the LIA, others show little evidence for a coherent hydroclimate response during these events. A better understanding of monsoonal dynamics during events like the MCA and LIA is needed in order to improve constraints on the relationship between temperature and hydroclimate variability, as well as to refine the global expression of the MCA and LIA. Here, decadally resolved physical, geochemical and isotopic lake sediment data from Badi Namco are used to investigate local and synoptic-scale ISM variability on the southeastern Tibetan Plateau during the last 3000 years. Physical and geochemical sediment data, including grain size, lithic flux, bulk density and XRF derived titanium (Ti) are used to characterize local variations in catchment erosion related to ISM rainfall. Synoptic ISM trends are characterized with leaf wax hydrogen isotopes (δDwax) that reflect the isotopic composition of summer precipitation. The Badi Namco results suggest that local ISM rainfall increased above the late Holocene average by 1200 cal yr B.P. and maintained elevated levels to the present, but with a slight decline after 200 cal yr B.P. Leaf wax hydrogen isotopes show a similar trend, but with a later ISM intensification (by 1000 cal yr B.P.) and a shorter event duration; δDwax increased sharply after minimum values at 600 cal yr B.P. These ISM variations inferred from the Badi Namco record share similarities with other local and regional paleoclimate records, including Indo-Pacific sea surface temperature (SST) reconstructions and foraminifera-derived upwelling in Arabian Sea. Together, these relationships suggest that the ISM intensified during the late Holocene after 1200 cal yr B.P. when Indo-Pacific SSTs were elevated. The Badi Namco results also support the idea that the MCA and LIA were relatively minor hydroclimate events on at least the southeastern Tibetan Plateau and that they occurred within the context of a more significant lower frequency climate event.
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