(ESH) A Modern Test of the Assumptions Used for Determining Paleo-Atmospheric Carbon Dioxide from Goethite-Bound Carbon

9628035施罗德使用针铁矿结合的碳同位素作为估算显生宙古大气二氧化碳的指标的概念一直是模拟工作的关键，例如伯纳(1994年)使用的GeoCARB模型。在这项研究中，我们建议测试Yapp(1992)(针铁矿推断的古大气二氧化碳方法的开发者)在现代针铁矿形成环境中所使用的基本假设。这项研究将使用在佐治亚州山前发现的覆盖花岗岩地形的土壤中形成的针铁矿进行。主要的研究地点是位于佐治亚州亚特兰大外25公里处的帕诺拉山研究分水岭(PMRW)。它是测试的最佳选择，因为发现了丰富的土壤针铁矿，它是被称为水、能源和生物地球化学预算(Webb)计划的美国地质调查局(USGS)大规模调查的一部分。PMRW进行了10多年的持续合作的水文、气候、地球化学和植物学研究，从而为研究针铁矿中的碳包裹体现象提供了一个有特色的背景。在这项研究中，我们建议：(1)在已建立的监测站进行土壤/尖晶石/母岩序列的高分辨率采样；(2)详细描述自生针铁矿的晶体化学性质，以解释以前被忽视的影响，如同象的A13取代对CO3=取代程度的影响；(3)对系统中的所有含碳组分，包括不同深度的大气和土壤CO2，土壤呼吸的CO2，生物和地下降解有机质，以及针铁矿中的碳进行稳定的碳同位素测量；(4)根据观测到的碳同位素剖面和浓度梯度评估针铁矿中碳包裹体的机制，以及(5)利用宇宙成因的10Be和26Al以及迄今未被测试的使用针铁矿中的14C的想法，在局部剥蚀率的背景下了解这一过程。这项工作的主要目标将是建立稳定的碳同位素物种(特别是针铁矿结合碳)与土壤/腐泥岩序列中其他碳成分之间的关键关系。这项工作对利用碳结合的针铁矿作为古大气二氧化碳替代品的可行性具有重要意义。这项提案要求在三年内筹集87,776美元，用于夏季工资、提取线升级、质谱仪维护、用于选定的宇宙核素(10Be、14C、26Al)加速器质谱仪的资金、消耗性用品和提交科学发现的资金。?？

9628035 Schroeder The concept of using goethite-bound carbon isotopes as a proxy for estimating paleo-atmospheric pCO2 throughout the Phanerozoic has been a kingpin for modeling efforts such as the GEOCARB model used by Berner (1994). In this study we propose to test the underlying assumptions used by Yapp (1992) (developer of the goethite inferred paleo-atmospheric pCO2 method) in a modern goethite forming environment. The study will be performed using goethite forming in soil-saprolite found overlying granite terrains in the Piedmont of Georgia. The principal study site is the Panola Mountain Research Watershed (PMRW) located 25 km outside of Atlanta, Georgia. It is optimal for the test because of the abundance of soil goethite found and it is part of the large-scale U.S. Geological Survey (USGS) investigation known as the Water, Energy and Biogeochemical Budget (WEBB) Program. The PMRW has seen over 10 years of continuous collaborative hydrologic, climatic, geochemical and botanical research, thus providing a well-characterized contextual backdrop to examine the phenomenon of carbon inclusion in goethite. In this study we propose to: (1) conduct high-resolution sampling of the soil/caprolite/parent rock sequence at established monitoring stations with the PMRW; (2) detail the crystal-chemical nature of the authigenic goethite in order to account for such previously ignored effects such as the isomorphous A13+ substitution on the degree of CO3= substitution; (3) make stable carbon isotopic measurement of all carbon-bearing components in the system including atmosphere and soil CO2 at various depths, soil-respired CO2, live and subsurface degrading organic matter, as well as the carbon in goethite; (4) evaluate the mechanism of carbon inclusion in goethite in the context of observed carbon isotopic profiles and concentration gradients, and (5) understand the process in the context of local denudation rates using cosmogenic 10Be and 26Al and the heretofore untested idea of using 14C, bound in goethite. The principal goal of this work will be to establish the critical relationships between the stable carbon isotopic species (particularly goethite-bound carbon) and other carbon components in a soil/saprolite sequence. This work has important implications for the viability of using carbon-bound goethite as a proxy for paleo-atmospheric CO2. This proposal solicits $87,776 over a three-year period to be used for Summer salary, extraction line upgrades, mass spectrometer maintenance, funds for selected cosmogenic nuclide (10Be, 14C, 26Al) accelerator mass spectrometry, expendable supplies and funds to present scientific findings. ??