Collaborative Research: Calibrating the paleosol carbonate CO2 barometer for vertic paleosols by monitoring soil CO2 in modern Vertisols

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。知识价值：提出了古土壤碳酸盐CO2气压计的校准，以改进对地球CO2浓度的估计。古老的气氛。在土壤碳酸盐形成过程中，土壤中的CO2浓度S(z)是使用气压计计算大气CO2浓度所必需的。最近的研究表明，沙漠土壤中的S(z)值明显低于晴雨表中通常使用的值，因为碳酸盐不是在以前假设的平均生长季节条件下形成的，而是在土壤足够干燥以限制呼吸（即土壤二氧化碳产生）的一年中形成的。如果利用先前编制的古土壤数据计算荒漠土壤的季节性低S(z)值，则大气CO2水平明显低于先前报道的水平（~1000 ppmV vs ~3000 ppmV）。在这些相对较低的二氧化碳浓度下，温室气候（温暖、无冰的地球）的持续存在表明，地球？地球表面温度对大气中二氧化碳的影响比目前认为的要敏感得多。对这种可能性的全面评估需要进一步的研究，因为沙漠土壤并不是古大气CO2研究中使用的大多数古土壤的最合适的现代模拟物。提出的研究旨在限制S(z)在现代垂直土壤，这是高粘土含量，高收缩膨胀潜力的土壤。本研究之所以选择垂直气溶胶，是因为它们的古代当量已被广泛用于重建古代大气中的二氧化碳。以下三部分的假设将被检验：1)土壤干燥降低呼吸速率，2)土壤的开裂（当它干燥时）允许呼吸的二氧化碳更快地从土壤中逸出，3)干燥和开裂导致的土壤二氧化碳浓度的降低导致了Vertisols中成土碳酸盐的形成。一系列的测量将在德克萨斯州的versols进行，以确定哪一部分的季节变化是由碳酸盐岩记录的。监测土壤CO2浓度、土壤CO2稳定同位素组成、土壤温度和土壤湿度，测定土壤成土碳酸盐稳定同位素组成。根据土壤CO2和碳酸盐之间的同位素平衡和方解石溶解度最低的时间，将确定成土碳酸盐形成的时间，以及s (z)的最合适值(s)。如果为s (z)确定的值与以前的研究结果有显著差异，则新的值将用于重新计算古大气CO2浓度，并估计古生代和中生代古垂直土壤的气候敏感性。更广泛的影响：预测即将到来的气候危机的严重程度是当今人类面临的最重要的科学挑战之一。拟议中的研究通过重新评估地球的敏感性，直接解决了这一挑战。气候变化导致大气中二氧化碳浓度升高。因此，拟议的研究最广泛的影响将是帮助预测未来的气候变化，并帮助决策者了解持续的、未经缓解的人为二氧化碳排放的潜在后果。从合作研究、研究生和本科教育到各种场合的公共宣传的相互智力利益，个人的熏陶将产生更直接和个人的影响。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Intellectual Merit: A calibration of the paleosol carbonate CO2 barometer is proposed in order to improve estimates of the concentration of CO2 in Earth?s ancient atmosphere. The concentration of CO2 in the soil during soil carbonate formation, S(z), is required in order to calculate atmospheric CO2 concentrations using the barometer. Recent research has shown that the value of S(z) in desert soils is significantly lower than values typically used in the barometer because carbonate does not form under mean growing season conditions as previously assumed but instead forms during times of year when the soil is sufficiently dry to limit respiration (i.e. soil CO2 production). Atmospheric CO2 levels that are significantly lower than previously reported (~1000 ppmV versus ~3000 ppmV) result if the seasonally low S(z) value determined for desert soils is used to calculate atmospheric CO2 concentrations from previously compiled paleosol data. The persistence of greenhouse climates (warm, ice-free Earth) under these relatively low CO2 concentrations suggests that the Earth?s surface temperature is much more sensitive to atmospheric CO2 than currently thought. A thorough evaluation of this possibility requires further study because desert soils are not the most appropriate modern analog for most paleosols used in paleoatmospheric CO2 studies. The proposed study is intended to constrain S(z) in modern Vertisols, which are high clay-content, high shrink-swell potential soils. Vertisols are chosen for this study because their ancient equivalents have been widely used to reconstruct ancient atmospheric CO2. The following three-part hypothesis will be tested: 1) drying of the soil reduces respiration rates, 2) cracking of the soil (when it is dry) allows respired CO2 to escape from the soil more rapidly and 3) the decrease in soil CO2 concentration resulting from both drying and cracking causes the formation of pedogenic carbonate in Vertisols. A suite of measurements will be carried out in Texas Vertisols to determine what portion of seasonal variability pedogenic carbonate records. The concentration of soil CO2, the stable isotope composition of soil CO2, soil temperature and soil moisture will be monitored and the stable isotope composition of pedogenic carbonate in the soil will be measured. The timing of pedogenic carbonate formation, and by association the most appropriate value(s) for S(z), will be determined based on when isotope equilibrium between soil CO2 and carbonate occurs and when minimum calcite solubility occurs. If the value(s) determined for S(z) are significantly different than those used in previous studies, the new values will be used to recalculate paleoatmospheric CO2 concentrations and to estimate climate sensitivity from Paleozoic and Mesozoic paleo-Vertisols. Broader Impacts: Predicting the severity of the impending climate crisis is one of the most important scientific challenges facing humanity today. The proposed research directly addresses this challenge by reevaluating the sensitivity of Earth?s climate to elevated atmospheric CO2 concentrations. Therefore, the broadest impacts of the proposed research will be to help predict future climate change and to help inform policy makers about the potential consequences of continued, unmitigated anthropogenic CO2 emissions. Personal edification, ranging from the mutual intellectual benefits of collaborative research to graduate and undergraduate education to public outreach in various venues, will have a more immediate and individual impact.