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

Texas A&M Research Foundation, College Station TX

Investigators

Abstract

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.