Interpreting Paleoclimate when Continental Positions are Uncertain: the Effects of Sampling, Modeling and Reconstructing

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Parrish 9627771 Paleogeographers and paleoclimatologists have tended to have very different agendas in studying paleoclimates, and their differing approaches and interests have led to a circularity in paleoclimatic studies that the proposed project is intended to address. The problem is greatest in studies of climates of the Paleozoic Era, when continental positions are likely to be poorly known. Paleoclimatologists have used available paleogeographic reconstructions as if they were independent of paleoclimatic data, but, in fact, some continental positions are determined at least partly from paleoclimatic data. The purpose of the proposed research is to: (1) document and evaluate the problems that arise from using paleoclimatic data to position continents, including such problems as non-uniquenessof positioning and the use of probability curves based on zonal climates for positioning continents that were likely to have had non-zonal climates: (2) establish more rigorous sampling procedures for the use of paleoclimatic data in both paleogeographic and paleoclimatic reconstruction. To address the problem of sampling, which refers not to how the data are collected but, rather, how they are compiled for use in a spatial fromat, we will develop a new grid system more appropriate for gridding data on a sphere that the latitude-longitude grid, which suffers from uneven grid-cell dimensions. We will then develop procedures for reporting the distribution of paleoclimatic indicators. This will permit evaluation of the robustness of the various assumptions that are made in this type of work. Finally, we will apply the developed methods to a persistent problem in Paleozoic paleogeography, that is, the positions of Gondwana in the Late Devonian. One possible outcome is that we will be able to eliminate one of the proposed positions, based on objectives evaluations of the data. A more likely outcome is that we will show where new data must be collected and which underlying assumptions must be examined to resolve the conflict. The broader implications of this project will be to enforce much more rigor into paleogeographic reconstructions, demonstrate the error introduced by circularity in using for paleoclimatic modeling paleogeographic reconstructions that are based at least in part on paleoclimatic indicators, and suggest procedures that might overcome the basic conflict between the needs of paleogeographers and those of paleoclimatologists.