COLLABORATIVE RESEARCH: Laminated soil carbonate rinds as a tool for investigating late Quaternary climate-vegetation links

美国西部等旱地的特点是降水量变化大，季节性高温。气候变化可能会影响这两个方面，增加未来发生干旱的可能性。植物是食物链的基础，因此了解它们如何应对气候变化非常重要。这项研究旨在进一步开发一种新的方法来创建过去植被，土壤温度和土壤水分蒸发的详细历史。这些历史可以追溯到数万年前，保存在土壤中形成的一种矿物碳酸钙（CaCO 3）中。这些矿物质在岩石的下面逐渐生长，世纪之后，世纪，形成“层状土壤碳酸盐外皮”。主要的植被组成，温度和土壤水分蒸发的程度记录在碳和氧化学（同位素），构成每一层。来自犹他州南部凯匹特礁/博尔德山地区几个地点的碳酸盐外皮将提供大约4万年前的详细记录。这些树皮的同位素记录将与区域和全球的其他记录进行比较，以更好地了解犹他州南部气候和植被变化的原因。该研究将回答以下问题：植物分布如何响应土壤温度和蒸发的变化？气候变化如何影响不同海拔的植物分布？从一个地方到另一个地方的记录有多可比？ 除了关于植物对气候变化反应的新知识外，这项研究还将通过以下方式使国家地球科学工作人员受益：（1）在本科、研究生和博士后水平上培训新一代地球科学专业人员（2）为国家公园工作人员提供继续教育，（3）为服务水平较低的高中生带来身临其境的科学外展体验。土壤碎屑底面形成层状碳酸盐外皮（从鹅卵石到大圆石）。在长寿命、稳定的地貌表面上，树皮可以生长10到100万年，并可以呈现有序、连续和详细的（世纪尺度）过去条件的地层，如稳定同位素所记录的。长期存在的地貌表面和层压外皮类似于洞穴和洞穴;层压外皮是一个有前途的，但未充分利用，记录过去的气候和植被过程的关键区域档案。在他以前的工作中，研究人员开发了一个单一的皮屑为基础的气候和植被记录，从南部犹他州的国会礁地区跨越5 - 35 ka。他们展示了如何基于二次离子质谱（西姆斯）的δ 13 C和δ 18 O记录，沿着由聚集同位素测温法提供的温度信息，可用于重建古代景观中C4植被比例的变化，δ 18 O-土壤水和过去的土壤温度。在目前的工作中，他们解决了重要的问题有关的可复制性在当地的区域尺度，并在现有的第四纪记录从美国西部的背景下，展示了调查权力的这个关键区档案古气候研究：是否每个外皮记录的故事，只有一个土壤，或记录可以横向外推？如何在土壤中的果皮位置（浅与深）影响记录？ 海拔样带的记录是如何变化的？ 果皮碳酸盐中的三重氧同位素对蒸发敏感吗？ 为了回答这些问题，他们将集中在一个核心集的四个rinds跨越海拔横断面从1750到2500米的约翰逊梅萨和托里台地貌表面（古泥石流）附近的国会礁国家公园，犹他州。另外六个外皮将用于调查更广泛的地理范围，并调查土壤深度的影响。他们将为每个剖面开发一个详细的放射性碳年龄模型，并通过高空间分辨率的西姆斯（~10 µm斑点直径;百年分辨率）分析外壳δ 13 C和δ 18 O。将以更高的分辨率（约1000毫米）生成成团和三重氧同位素剖面。2-3 kyr/样品），以及六个额外剖面的关键间隔（例如，最近，中全新世，LGM）。他们将根据土壤温度，pCO 2，土壤湿度和降雨量的现代数据集进行古气候推断。拟议的研究将产生若干详细的气候记录，对古代旱地关键区有新的了解，更好地了解记录提供的信息，并指导如何在其他地方最好地应用稳定的表层层压外皮方法。这项工作的更广泛的社会影响包括培训地球科学的本科生、研究生和博士后，继续教育国会礁国家公园的工作人员了解当地的地质和地貌，以及更新世之友实地考察这一地区。他们还将为密歇根大学的地球夏令营项目开发一个新的土壤、二氧化碳和气候模块，该项目为来自底特律服务水平低下社区的有前途的高中生提供为期一周的科学夏令营体验。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

Drylands such as those found in the western United States are characterized by high precipitation variability and seasonally-high temperatures. Climate change is likely to affect both, increasing the chances of drought in the future. Plants are the base of the food chain, so it is important to understand how they respond to climate variability. This research seeks to further develop a new way of creating detailed histories of past vegetation, soil temperature, and soil water evaporation. These histories, which can go back tens of thousands of years, are preserved in a mineral, calcium carbonate (CaCO3), that forms in soils. These minerals grow incrementally, century after century, on the undersides of rocks to form 'laminated soil carbonate rinds'. Prevailing vegetation composition, temperature, and degree of soil water evaporation are recorded in the carbon and oxygen chemistry (isotopes) that make up each layer. Carbonate rinds from several locations in the Capitol Reef / Boulder Mountain region of southern Utah will provide detailed records extending back approximately 40,000 years. Isotopic records from these rinds will be compared to other records regionally and globally to get a better understanding of the causes of climate and vegetation change in southern Utah. The research will answer questions such as: How do plant distributions change in response to changes in soil temperature and evaporation? How does climate change influence plant distributions at different elevations? How comparable are the records from one location to another? In addition to the new knowledge about plant responses to climate change, this study will benefit the national geoscience workforce through (1) training a new generation of geoscience professional at the undergraduate, graduate, and postdoctoral levels (2) providing continuing education for national park staff, and (3) bringing immersive scientific outreach experiences to under-served high school students.Laminated soil carbonate rinds form on the undersides of soil clasts (ranging from pebbles to boulders) in many dryland regions worldwide. On long-lived, stable geomorphic surfaces, rinds can grow for 10s to 100s of kiloyears, and can present ordered, continuous, and detailed (century-scale) stratigraphies of past conditions, as recorded by stable isotopes. The long-lived geomorphic surface and laminated rind are analogous to a cave and speleothem; laminated rinds are by extension a promising, but underutilized, critical zone archive recording past climate and vegetation processes. In his previous work, the investigators developed a single rind-based climate and vegetation record from the Capitol Reef region of southern Utah spanning 5 – 35 ka. They showed how Secondary Ion Mass Spectrometry (SIMS)-based delta 13C and delta 18O records, along with temperature information provided by clumped isotope thermometry, can be used to reconstruct changes in the fraction of C4 vegetation on the ancient landscape, delta 18O-soil water, and past soil temperature. In the present work, they address important questions related to replicability on local to regional scales and, within the context of existing Quaternary records from the western United States, demonstrate the investigative power of this critical zone archive for paleoclimate studies: Does each rind record the story of just one soil, or can records be extrapolated laterally? How does rind location within the soil (shallow versus deep) affect the record? How do records change across an elevation transect? Are triple oxygen isotopes in rind carbonate sensitive to evaporation? To answer these questions, they will focus on a core set of four rinds spanning an elevation transect from 1750 to 2500 m on the Johnson Mesa and Torrey Bench geomorphic surfaces (paleo-debris flows) near Capitol Reef National Park, Utah. Six additional rinds will be used to investigate a wider geographic range, and to investigate the effects of soil depth. They will develop a detailed radiocarbon age model for each profile, and analyze rind delta13C and delta18O via high spatial-resolution SIMS (~10 µm spot diameter; centennial resolution). Clumped and triple oxygen isotope profiles will be generated in higher resolution (ca. 2-3 kyr/sample) for the core rinds, and for key intervals (e.g. recent, mid-Holocene, LGM) for the six additional profiles. They will make paleoclimate inferences based on modern datasets of soil temperature, pCO2, soil moisture, and rainfall. The proposed research will result in several detailed climate records with novel insight into ancient dryland critical zones, a better understanding of what kind of information the records provide, and a guide for how to best apply the stable surface – laminated rind approach elsewhere. Broader societal impacts of the work include the training of undergraduate, graduate, and postdoctoral students in the geosciences, continuing education for Capitol Reef National Park staff in local geology and geomorphology, and a Friends of the Pleistocene field trip focusing on this region. They will also develop a new soils, CO2, and climate module for the University of Michigan's Earth Camp program, which provides promising high school students from underserved communities in Detroit with week-long science camp experiences.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.