(ESH) Miocene Concentrations and 13C of Atmospheric Carbon Dioxide Inferred from Stomatal Density and 13C of Fossil Leaves

将中新世植物叶片的稳定碳同位素比率和气孔特征与近缘缘植物叶片的稳定碳同位素比率和气孔特征进行比较。将分析近缘缘植物的标本室标本，以校正自工业革命以来大气二氧化碳浓度增加30%和同位素组成减少1.2%的同位素组成和气孔特征。利用这些校准，我们将从化石数据中获得10到20个独立的、特定于分类群的中新世大气中二氧化碳同位素组成和浓度的估计。这些树叶化石属于亚热带和温带树木，大约1500万年前沉积在爱达荷州克拉基亚附近的缺氧湖泊沉积物中。区系优势乔木有栎科、板栗科、伪木科、水杉科和紫杉科。这些保存完好的化石先前已经产生了DNA，分类群特定的类黄酮谱，有时当第一次从沉积物中取出时仍然有色素。据我们所知，它们是这个时代世界上保存最完好的标本。尽管如此，为了尽量减少成岩作用对同位素组成的影响，所有的比较都将依赖于从现代树叶和化石中提取的木质素。将在所有叶片的重复样本上测量气孔密度（每平方米叶表面气孔数）和气孔大小；尽可能测量气孔指数（#气孔/（#气孔+表皮细胞））。还将收集最新的现存近亲，以量化树冠位置和海拔高度的影响。中新世中期是气温和二氧化碳浓度迅速下降的时期。已发表的对大气成分的估计依赖于海洋沉积物的同位素数据，这些数据是不确定的，因为它们离大气有几步之遥。我们提出了一种基于与大气耦合更好的陆地植物的重建大气成分的替代方法。由于单个属可以单独分析，这项工作将提供每个属的大气成分的独立估计。如果成功，这项工作可能最终导致中新世陆地光合作用的分析，这是从大气中去除二氧化碳的主要生物地球化学过程之一，并可能限制我们对陆地生态系统对大气二氧化碳持续增加的响应的估计。

9510078 Marshall Stable carbon isotope ratios and stomatal characters of Miocene leaves will be compared to those of modern leaves from nearest living relatives (NLR) Herbarium specimens of the NLR's will be analyzed to calibrate isotopic composition and stomatal characters against the 30% increase in atmospheric carbon dioxide concentration and the 1.2% decrease in isotopic composition since the industrial revolution. Using the calibrations, we will obtain from the fossil data ten to twenty independent, taxon-specific estimates of the isotopic composition and concentration of carbon dioxide in the Miocene atmosphere. The fossil leaves are of subtropical and temperate trees deposited ca. 15 million years ago in anoxic lake sediments near clarkia, Idaho. The dominant trees in the flora included species of Quercus, Castanea, Pseudofagus, Metasequoia , and Taxodium. These remarkably preserved fossils have previously yielded DNA, taxon-specific flavonoid profiles, and are sometimes still pigmented when first removed from the sediments. They are, to our knowledge, the best preserved specimens of this age in the world. Nonetheless to minimize the influence of diagenesis on isotopic composition all comparisons will rely on lignin extracted from the modern leaves and the fossils. Stomatal density (# stomata per m2 of leaf surface) and stomatal size will be measured on replicate samples of all leaves; stomatal index (#stomata/(#stomata + epidermal cells)) will be measured where possible. New collections of the nearest living relatives will also be made to quantify the effects of canopy position and altitude above sea level. The middle Miocene was a time of rapidly falling temperatures and CO2 concentrations. Published estimates of atmospheric composition rely on isotopic data from ocean sediments, which are uncertain because they are several steps removed from the atmosphere. We propose an alternative means of reconstructing atmospheric composition based on land plants, which are better coupled to the atmosphere. Because individual genera can be analyzed separately, the work will provide an independent estimate of atmospheric composition from each genus. If successful, this work may eventually lead to analyses of Miocene terrestrial photosynthesis, one of the major biogeochemical processes removing CO2 from the atmosphere, and may constrain our estimates of terrestrial ecosystem responses to the ongoing increase in atmospheric CO2.