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。智力优点：古土壤碳酸盐CO2气压计的校准建议，以提高地球上的CO2浓度的估计？古老的氛围。为了使用气压计计算大气CO2浓度，需要土壤碳酸盐形成期间土壤中的CO2浓度S（z）。最近的研究表明，沙漠土壤中的S（z）值明显低于气压计中通常使用的值，因为碳酸盐并不像以前假设的那样在平均生长季节条件下形成，而是在一年中土壤足够干燥以限制呼吸作用（即土壤CO2产生）的时候形成。大气CO2水平显着低于以前报告（~1000 ppmV对~3000 ppmV）的结果，如果季节性低S（z）值确定的沙漠土壤用于计算大气CO2浓度从以前编译的古土壤数据。温室气候（温暖，无冰的地球）在这些相对较低的二氧化碳浓度下的持续性表明，地球？地球表面温度对大气中二氧化碳的敏感性比目前认为的要高得多。对这种可能性的全面评估需要进一步的研究，因为沙漠土壤不是最合适的现代模拟古大气CO2研究中使用的大多数古土壤。建议的研究是为了限制S（z）在现代变性土，这是高粘粒含量，高收缩膨胀潜力的土壤。之所以选择变性土进行这项研究，是因为它们的古代等价物已被广泛用于重建古代大气CO2。将检验以下三部分假设：1）土壤干燥降低呼吸速率，2）土壤开裂（干燥时）使呼吸的CO2更快地从土壤中逸出，3）干燥和开裂导致土壤CO2浓度降低，导致变性土中成壤碳酸盐的形成。将在得克萨斯变性土中进行一系列测量，以确定季节性变化的成壤碳酸盐记录的比例。将监测土壤CO2的浓度、土壤CO2的稳定同位素组成、土壤温度和土壤湿度，并测量土壤中成壤碳酸盐的稳定同位素组成。成壤碳酸盐形成的时间，并通过关联的S（z）的最合适的值（S），将根据土壤CO2和碳酸盐之间的同位素平衡发生时，当最小的方解石溶解度发生。如果确定的S（z）值与先前研究中使用的值有显著差异，则新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变性土的气候敏感性。预测即将到来的气候危机的严重性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。气候对大气CO2浓度升高的影响。因此，拟议研究的最广泛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、未减缓的人为二氧化碳排放的潜在后果。个人熏陶，从合作研究的相互智力利益到研究生和本科生教育，再到各种场所的公共宣传，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.