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

最近的事态发展首次为估计古生代大陆冰量的两种方法提供了机会：氧同位素(18O/16O)古测温和冰盖气候模型(ISCM)。这项提案要求提供资金，利用海洋化石和ISCM的氧同位素数据来估计地球过去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-冰室-温室旋回。作为第一步，该模型将在更近的末端成员气候上进行测试，这些气候包括晚更新世(完全冰化)和早始新世或中白垩世(无冰)。这将检验该模型再现温度分布的能力，并允许与现有的同位素数据进行比较。然后，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)的地球化学模型中输入，从而可以估计全球气温变化和冰量。使用腕足类贝壳的模拟温度和氧同位素(D18O)数据，可以计算海水d18O，并重新确定冰量。不同的二氧化碳水平将反复输入，以努力汇聚到一个温度分布、二氧化碳水平和冰量与同位素数据相互一致的溶液中。这项研究所需的许多数据都是从以前的研究中获得的，特别是来自第一个PI及其同事的研究。将利用手头的样品(由俄罗斯和澳大利亚的合作者提供，并在俄罗斯收集)收集选定的层段(例如，下石炭统和二叠纪早期)的额外数据。这将使开发可靠的晚古生代d18O记录成为可能。这项研究是开发一种确定冰量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结合在一起。最终目标是估计地球过去5.4亿年的大气二氧化碳水平。这项首次研究将使用计算机高效的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更昂贵的模型，集中于关键问题和模型/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.