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

旱地，如美国西部发现的旱地，具有高降雨量和季节性高温的特点。气候变化可能会影响到这两个地区，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是很重要的。这项研究试图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，保存在一种矿物碳酸钙(CaCO3)中，这种矿物形成于土壤中。这些矿物在岩石底部逐渐生长，一个世纪又一个世纪，形成“层状土壤碳酸盐岩皮”。普遍的植被组成、温度和土壤水分蒸发程度记录在构成每一层的碳和氧化学(同位素)中。来自犹他州南部国会礁/博尔德山地区多个地点的碳酸盐岩皮将提供可追溯到大约40,000年前的详细记录。来自这些冰盖的同位素记录将与地区和全球其他记录进行比较，以更好地了解犹他州南部气候和植被变化的原因。这项研究将回答以下问题：植物分布如何随着土壤温度和蒸发量的变化而变化？气候变化如何影响不同海拔地区的植物分布？从一个地点到另一个地点的记录可比性如何？除了有关植物应对气候变化的新知识外，这项研究还将通过(1)培训新一代本科生、研究生和博士后水平的地球科学专业人员(2)为国家公园工作人员提供继续教育，以及(3)为服务不足的高中生带来身临其境的科学推广体验，使国家地球科学工作者受益。在全球许多干旱地区，土壤碎屑(从鹅卵石到巨石)的底部形成了碳酸盐层状土壤。在长寿、稳定的地貌表面上，冰盖可以生长10s到100s的千年，并可以呈现由稳定同位素记录的过去条件的有序、连续和详细的(百年尺度)地层。长寿的地貌表面和层状皮类似于洞穴和洞穴；层状皮是一种有希望的、但未得到充分利用的关键区域档案，记录了过去的气候和植被过程。在他之前的工作中，研究人员从犹他州南部的国会珊瑚礁地区开发出了跨度为5-35ka的单一基于外壳的气候和植被记录。他们展示了如何使用基于二次离子质谱仪(SIMS)的三角洲13C和三角洲18O记录，以及由成束同位素测温提供的温度信息，来重建古地貌上的C4植被部分、三角洲18O-土壤水分和过去土壤温度的变化。在目前的工作中，他们解决了与地方到区域尺度上的可重复性有关的重要问题，并在美国西部现有的第四纪记录的背景下，展示了这一关键区域档案在古气候研究中的调查能力：每一层皮只记录了一种土壤的故事，还是记录可以横向推断？土壤中的皮位置(浅的还是深的)对记录有什么影响？高程横断面上的记录如何更改？碳酸盐岩中的三重氧同位素对蒸发敏感吗？为了回答这些问题，他们将重点研究犹他州国会礁国家公园附近约翰逊台地和托里板凳地貌表面(古泥石流)上的一组核心四个冰川，横跨从1750米到2500米的高程样带。另外六个绿地将被用来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详细的放射性碳年龄模型，并通过高空间分辨率SIMS(~10微米光斑直径；百年分辨率)分析Rind三角洲13C和Delta18O。将以更高的分辨率(约2-3KYR/样品)为岩芯皮生成成束和三重氧同位素剖面，并为另外六个剖面生成关键间隔(例如，最近、中全新世、大全新世)。他们将根据土壤温度、二氧化碳含量、土壤湿度和降雨量的现代数据集进行古气候推断。拟议中的研究将产生几个详细的气候记录，对古代旱地临界区有新的见解，更好地理解这些记录提供的信息，并指导如何在其他地方最好地应用稳定的表面叠层RIND方法。这项工作的更广泛的社会影响包括对本科生、研究生和博士后进行地球科学方面的培训，对国会礁国家公园工作人员进行当地地质和地貌学方面的继续教育，以及以该地区为重点的更新世之友实地考察。他们还将为密歇根大学的地球夏令营计划开发一个新的土壤、二氧化碳和气候模块，该计划为来自底特律服务不足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优势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.