Climate Dynamics of the Late Paleozoic Ice Age.

[摘要] The late Paleozoic era (~360-250 Ma) witnessed the vegetated Earth’s only knowntransition from an icehouse to a greenhouse climate. This transition brought Earthfrom the Phanerozoic’s most severe glaciation, the late Paleozoic ice age (LPIA), intoa greenhouse climate that would dominate the next 220 million years of Earth history.Developing an understanding of the late Paleozoic icehouse climate and the mechanismsthat drove Earth into a protracted greenhouse state are fundamental to thestudy of climate dynamics in both the distant past and the near future. The traditionalunderstanding of late Paleozoic climate contends that massive continental-scaleice sheets formed when the southern hemisphere land masses were located near to theaustral 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 LPIAclimate was much more dynamic. In addition to ice sheets waxing and waning onorbital time-scales, the emerging view of LPIA climate contends that icehouse conditionswere episodic, divided by multiple intervals (~10 Myrs) of ice-free greenhouseconditions. This newfound variability in the LPIA climate state has been hypothesizedto result from fluctuations in atmospheric carbon dioxide concentrations. To constrainthe climatic dynamics discussed in these disparate LPIA views, this dissertation employsnumerical climate-modeling techniques to explore the interactions of the latePaleozoic 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.

[发布机构] University of Michigan

[效力级别] Carbon Dioxide

[关键词] Paleozoic;Carbon Dioxide;Ecosystem Feedbacks;Orbital Forcing;Ice Sheets;Climate Change;Atmospheric;Oceanic and Space Sciences;Geology and Earth Sciences;Science;Geology