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。反映末次冰期-间冰期大尺度大气环流变化的记录相对较少，具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的记录也很少。要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陆地古气候记录，但跨越最后几个冰期-间冰期旋回的记录相对较少。这些稀疏的记录已被证明不足以解决在冰期-间冰期过渡期间发生的大规模有效水分变化背后的机制。此外，利用现有的代用数据从降水量变化中解析温度和水汽源变化的影响也具有一定的挑战性。智力优势：该项目将开发使用次级离子质谱（SIMS）的高空间分辨率分析方法，利用成土蛋白石提供过去几次冰期-间冰期（10至200 ka）气候和大气环流的空间和时间连续记录。230 - u SIMS定年将得到多同位素代用物发展的补充，以便建立连接形成区域网格的高时空分辨率记录，从而能够独特地反映过去大气环流的变化。具体来说，研究人员将验证一个假设，即铀同位素和微量元素在年代成土蛋白石中的变化为古沉淀提供了一个可靠的档案。湿度源的变化将使用&amp；#948；18O，风化强度的变化将用&amp；#948；30Si来评估。现有的土壤年代学记录显示，在过去200 ka中，初始（234U/238U）活度比和微量元素发生了变化。研究者假设最初的（234U/238U）变化记录了过去降雨量的变化。然而，在开发定量数据之前，必须更仔细地检查这些变化的确切机制。因此，在扩大土壤站点网络之前，她建议使用现代土壤系统测试初始（234U/238U）值与u系列代理的有效性的一致性。u系列代用物的开发和验证将使古气候信息能够直接从土壤的地质年代学测量中提取出来，并有可能扩展到洞穴中。更广泛的影响：这项研究将对我们理解陆地环境中气候变化的速率和机制具有重要意义。通过与气候模拟社区合作，数据和站点网络将提供独特和急需的校准数据，这将大大提高预测和理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，她所开发的方法和理解也将对这些材料产生重要影响，并可能使在地球上的关键间隔开发新的记录。年代的历史。为了提供她的记录，她将在斯坦福大学主持一个已发表的u系列数据数据库，并与其他科学家合作，将现有记录纳入其中。其次，她将参与斯坦福大学地球科学学院的外展项目。她计划：1)接受高中实习生与她一起在实地和实验室工作；2)与K-12课程合作。拓展视野？开发一个模块来描述气候系统，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.