Climate Dynamics of the Late Paleozoic Ice Age.

Abstract

The late Paleozoic era (~360-250 Ma) witnessed the vegetated Earth’s only known transition from an icehouse to a greenhouse climate. This transition brought Earth from the Phanerozoic’s most severe glaciation, the late Paleozoic ice age (LPIA), into a greenhouse climate that would dominate the next 220 million years of Earth history. Developing an understanding of the late Paleozoic icehouse climate and the mechanisms that drove Earth into a protracted greenhouse state are fundamental to the study of climate dynamics in both the distant past and the near future. The traditional understanding of late Paleozoic climate contends that massive continental-scale ice sheets formed when the southern hemisphere land masses were located near to the austral pole and repetitively waxed and waned due to orbital insolation variations. A recent re-analysis of the temporal and geographic distribution of glacial deposits, in conjunction with a re-examination of glacioeustasy records, indicates that LPIA climate was much more dynamic. In addition to ice sheets waxing and waning on orbital time-scales, the emerging view of LPIA climate contends that icehouse conditions were episodic, divided by multiple intervals (~10 Myrs) of ice-free greenhouse conditions. This newfound variability in the LPIA climate state has been hypothesized to result from fluctuations in atmospheric carbon dioxide concentrations. To constrain the climatic dynamics discussed in these disparate LPIA views, this dissertation employs numerical climate-modeling techniques to explore the interactions of the late Paleozoic atmosphere, biosphere, cryosphere, hydrosphere, and lithosphere. The studies presented in this dissertation confine the late Paleozoic icehouse/greenhouse atmospheric carbon dioxide threshold, test the effects of changing orbital insolation on ice sheet volume, present an orbitally-induced ecosystem feedback mechanism that facilitates ice sheet advance and retreat, and develops an orbitally-paced model of cyclic sediment deposition consistent with climate dynamics and field-based observations.