High-resolution records of atmospheric circulation and past rainfall from soils based on U-series and stable isotope SIMS approaches

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。在末次冰期-间冰期循环期间，反映大气环流大规模变化的记录相对较少，并且很少有足够的时间分辨率和/或连续性来解决变化的时间和顺序。为了了解这些变化在过去是如何发生的，对降水变化敏感的陆地气候记录是必要的。虽然有大量的短期高分辨率的陆地古气候记录，有相对较少的记录，跨越最后几个冰期-间冰期循环。这些稀疏的记录已被证明不足以解决冰川-间冰期过渡期间发生的有效水分大规模变化背后的机制。此外，利用现有的代用数据来解决降水量变化对温度和水分来源变化的影响也是一项挑战。本项目将利用二次离子质谱法开发高空间分辨率分析方法，提供最近几次冰期-间冰期过渡期间气候和大气环流的时空连续记录（10 ~ 200 ka）。230 Th-U西姆斯测年将通过开发多同位素代理来补充，以开发连接形成区域网格的高时间空间分辨率记录，从而独特地能够反映过去大气环流的变化。具体来说，研究人员将测试的假设，铀同位素和微量元素的变化，在过时的成壤蛋白石提供了一个强大的档案古沉淀。将使用#948; 18 O检测水分来源的变化，并使用#948; 30 Si评估风化强度的变化。现有的土壤年代学记录显示，在过去的200 ka的初始（234 U/238 U）的活动比和微量元素的变化。研究人员假设，初始（234 U/238 U）变化记录了过去降雨量的变化。然而，这些变化的确切机制，必须更仔细地检查之前，可以开发定量数据。因此，在扩展土壤站点网络之前，她建议使用现代土壤系统测试初始（234 U/238 U）值的一致性和U系列代理的有效性。开发和验证的U-系列代理将使古气候信息直接从土壤的地质年代学测量，并有可能被扩展到speleothem.Broader影响：这项研究将有重要的影响，我们的理解的速率和机制的气候变化在陆地环境。通过与气候建模社区合作，数据和站点网络将提供独特且急需的校准数据，这将大大提高预测和了解当前大气环流变化的能力。由于她计划分析的样本是古土壤的现代类似物，因此她开发的方法和理解也将对这些材料产生重要影响，并可能使新记录在地球的关键时间间隔被开发出来？的历史。为了使她的记录可用，她将在斯坦福大学主持一个已发表的U系列数据的数据库，并与其他科学家合作，包括现有的记录。其次，她将与斯坦福大学地球科学学院的外展计划合作。她计划：1）接受高中实习生与她一起在现场和实验室工作，2）与K-12项目合作？拓展你的视野？开发一个描述气候系统的模块，它在过去是如何变化的，以及它是如何影响当地环境和大加州的景观的。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).There are relatively few records that reflect large-scale changes in atmospheric circulation during the last glacial-interglacial cycle, and very few with sufficient temporal resolution and/or continuity to resolve the timing and sequence of changes. To understand how these changes occurred in the past, terrestrial climate records that are sensitive to changes in precipitation are necessary. Although there are a substantial number of short-term high-resolution terrestrial paleoclimate records, there are relatively few records that span the last few glacial-interglacial cycles. These sparse records have proven insufficient to resolve the mechanisms behind the large-scale shifts in effective moisture that occurred during glacial-interglacial transitions. In addition, it has been challenging to resolve the effects of temperature and changes in moisture source from changes in the amount of precipitation using existing proxy data.Intellectual merit: This project will develop high-spatial resolution analytical approaches using secondary ion mass spectrometry (SIMS) to provide spatially and temporally continuous records of climate and atmospheric circulation over the last few glacial-interglacial transitions (10 to 200 ka) using pedogenic opal. 230Th-U SIMS dating will be complimented by the development of multi-isotope proxies in order to develop high-temporal spatial resolution records that connect to form a regional grid, and are thus uniquely capable of reflecting past changes in atmospheric circulation. Specifically, the investigator will test the hypothesis that uranium isotopic and trace element variations in dated pedogenic opal provide a robust archive of paleoprecipitation. Changes in moisture sources will be detected using δ18O, and changes in weathering intensity will be assessed using δ30Si. The existing geochronological records from soils show variations in initial (234U/238U) activity ratios and trace elements over the last 200 ka. The investigator hypothesizes that initial (234U/238U) variations are recording changes in past rainfall amounts. However, the exact mechanism for these variations must be more closely examined before quantitative data can be developed. Therefore prior to expanding her network of soil sites, she proposes to test the concordance of the initial (234U/238U) values and the validity of the U-series proxy using the modern soil system. Development and validation of the U-series proxy would enable paleoclimate information to be extracted directly from the geochronologic measurements of soils and could potentially be extended to speleothem.Broader impacts: This research will have important implications for our understanding of the rates and mechanisms of climate change in terrestrial environments. By working with the climate modeling community, the data and network of sites will provide unique and much needed calibration data that will greatly improve the ability to predict and understand the current changes in atmospheric circulation. As the samples she plans to analyze are modern analogues for paleosols, the approaches and understanding she develops will also have important implications for these materials and may enable new records to be developed at key intervals back in Earth?s history. To make her records available, she will host a database of published U-series data at Stanford, and work with other scientists to include existing records. Secondly, she will work with the outreach program in the School of Earth Sciences at Stanford. She plans to: 1) accept high school interns to work with her in the field and in her laboratory, 2) work with the K-12 program ?Expanding Your Horizons? to develop a module describing the climate system, how it varied in the past, and how it has influenced the landscape of both the local environment and greater California.