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

9510078马歇尔 中新世叶片的稳定碳同位素比和气孔特征将与现代叶片的近亲（NLR）进行比较。NLR的植物标本将进行分析，以校准同位素组成和气孔特征，以对抗自工业革命以来大气中二氧化碳浓度增加30%和同位素组成减少1.2%的情况。 使用校准，我们将从化石数据中获得10到20个独立的，分类特定的估计同位素组成和浓度的二氧化碳在中新世的大气。 化石叶是亚热带和温带树木的沉积约。1500万年前在爱达荷州克拉克亚附近的缺氧湖泊沉积物中。 植物群中的优势树种包括栎属、栗属、赤杨属、水杉属和红豆杉属。 这些保存完好的化石以前已经产生了DNA，分类特异性的黄酮类化合物，有时在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品上测量气孔密度（每平方米叶表面的气孔数量）和气孔大小;如可能，将测量气孔指数（气孔数量/（气孔数量+表皮细胞））。 还将收集最近的亲属，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，因为它们距离大气有几步之遥。 我们提出了一种替代手段重建大气成分的基础上，陆地植物，这是更好地耦合到大气。 由于个别属可以单独分析，这项工作将提供一个独立的估计，从每个属的大气成分。 如果成功的话，这项工作可能最终导致对中新世陆地光合作用的分析，这是去除二氧化碳的主要地球化学过程之一。 来自大气的二氧化碳，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反应的估计。

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.