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

这项奖励是根据2009年《美国复苏和再投资法案》(公法111-5)资助的。这笔赠款增进了我们对亚洲季风系统应对岁差强迫的水文变异性的理解。这项工作使用新的方法从中国黄土高原地区收集的沉积物中产生定量的古降雨重建。这些记录以可供气候模型使用的形式提供了对亚洲季风强度的定量衡量(例如，以毫米/年为单位的降雨量)。这项工作主要集中在80-145kaBP和海洋同位素第11阶段(340-420kaBP)。在80-145kaBP之间，由于高度偏心，季风强度似乎受到进动期的太阳强迫的强烈影响。在MIS11期间，由于低偏心率，气候的岁差强迫可能已经减少。来自中国洞穴的稳定同位素记录证实，在80-145kaBP之间存在着与北半球夏季低纬日照变化密切相关的降水突变。虽然这些石笋记录提供了日期准确的高分辨率记录，这些记录明显与区域水文变化有关，但将这些记录转换为易于输入气候模型的形式更加困难，因为温度、水/岩石相互作用、水分输送或喷发降水过程中的分馏效应以及水汽来源效应都会影响石笋中记录的稳定同位素。生成了定量的古降雨记录，并利用该记录从黄土高原获得了80ka长的降雨记录。黄土高原降水量与中国洞穴和葫芦洞洞穴记录的del-18O高度相关，被广泛认为是亚洲季风强度的有力记录。这项研究是与中国科学院地球环境研究所黄土与第四纪地质国家重点实验室合作进行的，位于西安的中国。他们将为实地工作和磁化率测量提供后勤支持。240个样品将在大约500年的分辨率下测量10Be和磁化率，跨边界的样品分辨率较高，表明降水的变化率很高。OSL测年将用于生成年龄模型，在可能的情况下，将通过与U/Th年代测定的洞穴组同位素记录的关联来微调该模型。10Be样品制备和加速器质谱计测量将在亚利桑那大学的NSF-Arizona AMS设施中进行。部分工作将由亚利桑那大学的一名研究生进行，作为博士项目的一部分，为这名学生提供教育和培训机会。通过以一种易于纳入气候模型的格式提供高分辨率的古气候记录，这一提议的更广泛影响有助于确定岁差强迫如何影响亚洲季风强度，从而更好地理解气候突变的原因。这些结果也可能有助于消除控制洞穴群del-18O记录的相互竞争的影响。

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.