Quantitative paleorainfall reconstruction from the Chinese Loess Plateau using 10Be and magnetic susceptibility

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).This grant improves our understanding of the hydrologic variability associated with the Asian Monsoon system in response to precessional forcing. The work generates quantitative paleorainfall reconstructions from sediments collected from the Chinese Loess Plateau region using new methods. These records provide a quantitative measure of the strength of the Asian Monsoon in a form that can be used by climate models (e.g. rainfall in mm/yr). The work focuses on the periods 80-145 kaBP and Marine Isotope Stage 11 (340-420 kaBP). Between 80-145kaBP monsoon intensity appears to have been strongly influenced by insolation forcing at precessional periods as a result of high eccentricity. During MIS 11, precessional forcing of climate is likely to have been reduced because of low eccentricity. Stable isotope records from Chinese speleothems confirm the presence of abrupt and substantial changes in precipitation between 80-145 kaBP that are highly correlated with changes in low latitude northern hemisphere summer insolation. While these stalagmite records provide well-dated high-resolution records that are clearly related to regional hydrologic changes, translating these records into a form that is easily imported into climate models is more difficult because temperature, water/rock interactions, fractionation effects during moisture transport or during speleothem precipitation, as well as moisture source effects all can influence the stable isotopes recorded in a stalagmite. Quantitative paleorainfall records are generated and used to derive an 80-ka long rainfall record from the Loess Plateau. Precipitation amount on the Loess Plateau is highly correlated with the speleothem del-18O records from Dongge and Hulu caves in S.E. China, which are widely regarded as a robust record of Asian Monsoon intensity.This study is being conducted in collaboration with the State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, in Xi'An China. They will provide logistical support for the fieldwork and magnetic susceptibility measurements. 240 samples will be measured for 10Be and magnetic susceptibility at circa 500 year resolution, with higher sample resolution across boundaries showing a high rate of change of precipitation. OSL dating will be used to generate an age model which, where possible, will be fine tuned by correlation with U/Th dated speleothem isotope records. 10Be sample preparation and accelerator mass spectrometer measurements will be made at the NSF-Arizona AMS facility at the University of Arizona. Part of the work will be conducted by a graduate student at the University of Arizona, as part of a PhD project, providing educational and training opportunities for this student. By providing high-resolution paleoclimate records in a format easily incorporated into climate models, the broader impacts of this proposal help define how precessional forcing influences the Asian Monsoon intensity, leading to a better understanding of the causes of abrupt climate change. These results may also help deconvolve the competing influences that control speleothem del-18O records.