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

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。该赠款提高了我们对与亚洲季风系统响应岁差强迫相关的水文变化的理解。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。这些记录提供了亚洲季风强度的定量测量，其形式可用于气候模型（例如以mm/年为单位的降雨量）。研究重点是80-145 kaBP和海洋同位素阶段11（340-420 kaBP）。80- 145 kaBP之间的季风强度似乎已强烈影响到岁差周期的太阳辐射强迫的结果，高偏心率。在MIS 11期间，由于低偏心率，气候的岁差强迫可能已经减少。中国洞穴沉积物的稳定同位素记录证实了80-145 kaBP降水的突变和显著变化，这与低纬北方夏季日照变化高度相关。虽然这些石笋记录提供了与区域水文变化明显相关的日期明确的高分辨率记录，但将这些记录转换为易于导入气候模型的形式更为困难，因为温度，水/岩石相互作用，水分输送或洞穴沉积物沉淀期间的分馏效应以及水分源效应都可能影响石笋中记录的稳定同位素。定量古降雨记录的产生和使用，以获得一个80万年的降雨记录从黄土高原。黄土高原降水量与东南部东葛洞和葫芦洞洞穴沉积物的del-18 O记录有很好的相关性。这项研究是与位于中国Xi的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。他们将为野外工作和磁化率测量提供后勤支持。将以大约500年的分辨率测量240个样品的10 Be和磁化率，其中跨越边界的更高样品分辨率显示出降水的高变化率。光释光测年将用于生成一个年龄模型，在可能的情况下，将通过与U/Th测年洞穴沉积物同位素记录的相关性进行微调。10 Be样品制备和加速器质谱仪测量将在亚利桑那大学的NSF-亚利桑那AMS设施进行。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式的格式提供高分辨率的古气候记录，该提案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，从而更好地了解气候突变的原因。这些结果也可能有助于反卷积控制洞穴沉积物del-18 O记录的竞争影响。

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.