--> Abstracts: Role of Paleogeography and Carbon Dioxide in Governing Past Ocean and Atmospheric Circulation, by BARRON, ERIC J.; #90938 (1997)

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Abstracts: Role of Paleogeography and Carbon Dioxide in Governing Past Ocean and Atmospheric Circulation

BARRON, ERIC J.

Since the advent of plate tectonic theory, changing geography has been a primary explanation of the major ice ages and warm climate episodes of Earth history. Importantly, geographic variables, such as large-scale sea level changes, are well correlated with paleotemperatures. However, the application of a wide range of climate models suggests that paleogeography alone is insufficient to explain these large variations in climate. In fact, because of a number of different feedbacks, geography appears to explain only a small fraction of the 6--10°C fluctuations in the Earth's mean temperature compared with the present day. Geochemical mass balance models and isotopic measurements suggest that atmospheric carbon dioxide levels have also varied considerably through Earth history. Increases and decreases in atmospheric carbon dioxide levels produce substantial temperature changes and have considerable potential for explaining large changes in the Earth's mean temperature. In addition, based on geochemical mass balance arguments, changes in carbon dioxide concentration can be tied directly to plate tectonics, thus explaining the strong correlation between past geography and climate.

In a variety of cases (e.g., Eocene and Cretaceous), however, the combination of geography and carbon dioxide explains the changes in globally-averaged surface temperature, but not the distribution of surface temperatures. Climate models alone do not achieve conditions of polar warmth, particularly if the equatorial temperatures are similar to or are cooler than present-day temperatures. This problem is demonstrated by comparison of middle Cretaceous experiments with the distribution of temperatures from equatorial to polar latitudes. To solve this problem a change in the distribution of the equator-to-pole energy balance is required. One of the most logical solutions to this enigma is to invoke changes in poleward heat transport by the deep oceans; however, to date, the importance of this mechanism has not been demonstrated.

AAPG Search and Discovery Article #90938©1997-1998 AAPG Distinguished Lecturers