Constraining Late Paleozoic Climate, CO2 Levels, and Ice Sheet Volumes: Integration of Oxygen Isotopes with Climate and Ice Sheet Models

最近的发展为首次将两种估算古生代大陆冰体积的方法结合起来提供了机会：氧同位素（18O/16O）古温学和冰盖气候模式（iscm）。该提案要求资金使用海洋化石和iscm的氧同位素数据来估计地球过去一个关键时期的温度变化、冰量和二氧化碳水平。这项研究将跨越泥盆纪晚期到二叠纪中期，这是地球上最后一个温室-冰-温室循环。作为第一步，该模型将在更近的末期气候中进行测试，即晚更新世（完全冰川）和早始新世或中白垩纪（无冰）的气候。这将检验该模型重现温度分布的能力，并允许与现有同位素数据进行比较。该模型将以两种模式应用于古生代。首先，二氧化碳水平将从Berner （1997, Science 76:544-546）的地球化学模型输入，从而可以估计全球温度变化和冰量。利用模拟温度和腕足动物壳的氧同位素（d18O）数据，可以计算海水d18O并重新确定冰体积。将迭代输入不同的CO2水平，以努力收敛于温度分布、CO2水平和冰体积与同位素数据相互一致的解决方案。这项研究所需的许多数据都可以从以前的研究中获得，特别是从第一位PI和他的同事那里获得的。将使用俄罗斯和澳大利亚合作者提供的、在俄罗斯收集的手头样品，在选定的层段（例如，下石炭世和早二叠世）收集额外的数据。这将为晚古生代提供一个可靠的d18O记录。这项研究是开发确定冰体积和二氧化碳水平的新方法的第一步，该方法将冰盖和气候的物理动力学与通过氧同位素分析获得的精确数据相结合。最终目标是估算地球过去5.4亿年大气中的二氧化碳水平。这项初步研究将使用计算机高效ISCM进行，因为要检查的参数空间区域禁止使用更昂贵的模型。随后的研究将采用更复杂和昂贵的模型来关注关键问题和模型/数据不一致的领域。

Recent developments provide an opportunity to couple for the first time two methods for estimating Paleozoic continental ice volume: oxygen isotope (18O/16O) paleothermometry and ice sheet-climate models (ISCMs). This proposal requests funds to use oxygen isotopic data for marine fossils and ISCMs to estimate temperature variations, ice volumes, and CO2 levels during a key interval in Earth's past. The study will span late Devonian to mid-Permian time, Earth's last greenhouse-icehouse-greenhouse cycle. As a first step, the model will be tested on more recent end-member climates, those of the late Pleistocene (fully glaciated) and the Early Eocene or Mid-Cretaceous (ice free). This will examine the model's ability to reproduce temperature distributions and permit comparison to existing isotopic data. The model will then be applied to the Paleozoic in two modes. First, CO2 levels will be inputted from the geochemical model of Berner (1997, Science 76:544-546), permitting estimates of global temperature variation and ice volume. Using modeled temperatures and oxygen isotopic (d18O) data from brachiopod shells, seawater d18O can be calculated and ice volume redetermined. Different CO2 levels will be entered iteratively in an effort to converge on a solution in which the temperature distribution, CO2 level, and ice volume are mutually consistent with the isotopic data. Much of the data necessary for the study are available from previous studies, especially from those of the first PI and his coworkers. Additional data will be collected for select intervals (e.g., Lower Carboniferous and Early Permian) using samples in hand, provided by Russian and Australian collaborators, and collected in Russia. This will permit development of a reliable d18O record for the Late Paleozoic. This study is the first exploratory step in the development of a new methodology for determining ice volume and CO2 levels, in which the physical dynamics of ice sheets and climate are combined with the precise data available through oxygen isotope analysis. The ultimate goal is to estimate atmospheric CO2 levels for Earth's last 540 million years. This premiere study will be performed using a computer-efficient ISCM, as the areas of parameter space to be examined prohibit the use of more expensive models. Subsequent studies will employ more sophisticated and expensive models to focus on key problems and areas of model/data disagreement.