Stable Isotope Profiles in Modern Desert Soils

成土碳酸盐岩稳定同位素资料对我们了解陆地环境具有重要意义。成壤碳酸盐的DeltaC 13值受土壤中C3与C4生物量的比率的影响，该比率随大气P（CO2）和降水的季节性变化而变化。DeltaO 18值反映了当地的大气降水，这与气候直接相关。然而，从成壤碳酸盐岩中提取的信息量是有限的，因为有关其形成的某些假设从未经过检验。问题包括：1）碳酸盐是在特定的季节还是在不经意的风暴事件之后形成的？2)碳酸盐与土壤CO2和土壤水在同位素平衡中形成吗？3)是否有不同的生物群落（除了C3/C4比值）的独特特征，可以用来更好地模拟古成土碳酸盐岩的碳同位素测量？我们解决这些问题，通过测量土壤CO2和水的同位素组成作为深度的函数，并将这些数据与现代（晚全新世）土壤中的新碳酸盐的测量值进行比较。还将全年监测其他几个控制deltaC 13土壤CO2的参数，以确定温度和湿度变化的变化。这项研究的结果将允许更详细和准确的重建古气候利用土壤碳酸盐地球化学。我们已经确定了两个网站的研究：1）的皮埃蒙特的桑迪亚山脉以东的阿尔伯克基和2）塞维利亚国家野生动物保护区（SNWR），位于约1小时以南的阿尔伯克基。SNWR是理想的，因为它包含了四个不同生物群落的融合。在过去的100年里，这些生物群落随着气候变化而迁移，使我们能够评估成壤碳酸盐中发生的溶解/再沉淀的程度。这项研究所需的所有分析技术都已得到充分审查。我们开发了一种简单的技术，用于提取和测量土壤CO2的Δ C 13和Δ O 18值，另一种用于分析亚毫米量土壤水的Δ O 18值。我们已经证明了我们有能力测量土壤剖面中新生碳酸盐的δ C13和δ O 18值。该项目将受益于两个PI的专业知识，夏普稳定同位素地球化学，麦克法登土壤成因和土壤碳酸盐形成的建模。更广泛的影响：这项工作涉及研究生，本科生和K-12水平的重要学生研究组成部分。它构成了博士学位的基础。丹Breecker的研究，并将使他接触到广泛的地球化学分析技术，除了广泛的实地工作相结合的土壤学与地球化学。UNM被指定为少数民族服务机构，是该国仅有的四个研究/博士广泛机构之一，也被指定为西班牙裔服务机构。与以往一样，我们将招收几名少数民族本科生承担高级荣誉论文，作为他们教育的一部分，并为项目的利益。最后，我们希望有几个美国宇航局夏普学生（美国宇航局资助的少数民族/女学生暑期实习）在11/12年级的水平上工作这个项目的一个方面。PI夏普已经有五个成功的NASA夏普学生在各种项目工作。

The information available from stable isotope data of pedogenic carbonates has proven invaluable in our understanding of the terrestrial environment. DeltaC13 values of pedogenic carbonate are influenced by the ratio of C3 to C4 biomass in soils, which varies with changes in atmospheric p(CO2) and the seasonality of precipitation. DeltaO18 values reflect local meteoric water, which is directly tied to climate. The amount of information that can be extracted from pedogenic carbonates is limited, however, because certain assumptions regarding their formation have never been tested. Questions include: 1) Do carbonates form during a particular season or following discreet storm events?; 2) Do carbonates form in isotopic equilibrium with soil CO2 and soil water?; 3) Are there distinct characteristics of different biomes (in addition to C3/C4 ratios) that can be used to better model carbon isotope measurements of ancient pedogenic carbonate? We address these questions by measuring the isotopic composition of soil CO2 and water as a function of depth and comparing these data with measured values of neoform carbonate in modern (late Holocene) soils. Several other parameters that control deltaC13soil CO2 will also be monitored throughout the year to identifying variability in response to changes in temperature and moisture. The results of this study will allow for more detailed and accurate reconstruction of paleoclimate using soil carbonate geochemistry.We have identified two sites for the study: 1) the piedmont of the Sandia mountains east of Albuquerque and 2) the Sevilleta National Wildlife Refuge (SNWR), located approximately 1 hour south of Albuquerque. The SNWR is ideal because it encompasses the convergence of four distinct biomes. These biomes have migrated over the last 100 years in response to climate change, allowing us to evaluate the degree of dissolution/reprecipitation that occurs in pedogenic carbonate. All analytical techniques required for this study have been fully vetted. We have developed a simple technique for extracting and measuring the deltaC13 and deltaO18 values of soil CO2, and another for analyzing the deltaO18 value of sub-millimeter amounts of soil water. We have demonstrated our ability to measure the deltaC13 and deltaO18 values of neoform carbonates in soil profiles. The project will benefit from the expertise of the two PIs, Sharp for stable isotope geochemistry, and McFadden for soil genesis and modeling of soil carbonate formation.Broader impacts: This work involves a significant student-research component at graduate, undergraduate and K-12 levels. It forms the basis of a Ph.D. study by Dan Breecker and will expose him to a wide range of geochemical analytical techniques in addition to the extensive field work combining pedology with geochemistry. UNM is designated as a Minority Serving Institution and is one of only four Research/Doctoral-Extensive institutions in the country to also be designated as a Hispanic Serving Institution. As in the past, we will recruit several minority undergraduate students to undertake senior honor's theses as part of their education and for the benefit of the project. Finally we expect to have several NASA SHARP students (NASA funded summer internships for minority/women students) at the 11th/12th grade level working on an aspect of this project. PI Sharp has already had five successful NASA SHARP students working on various projects.