HR: 09:45h
AN: PP31F-08    [Abstracts]
TI: Thermal Transgressions and Phanerozoic Extinctions
AU: * Worsley, T R
EM: worsley@ohio.edu
AF: Ohio University, Department of Geological Sciences 316 Clippinger, Athens, OH 45701, United States
AU: Kidder, D L
EM: kidder@ohio.edu
AF: Ohio University, Department of Geological Sciences 316 Clippinger, Athens, OH 45701, United States
AB: A number of significant Phanerozoic extinctions are associated with marine transgressions that were probably driven by rapid ocean warming. The conditions associated with what we call thermal transgressions are extremely stressful to life on Earth. The Earth system setting associated with end-Permian extinction exemplifies an end-member case of our model. The conditions favoring extreme warmth and sea-level increases driven by thermal expansion are also conducive to changes in ocean circulation that foster widespread anoxia and sulfidic subsurface ocean waters. Equable climates are characterized by reduced wind shear and weak surface ocean circulation. Late Permian and Early Triassic thermohaline circulation differs considerably from today's world, with minimal polar sinking and intensified mid-latitude sinking that delivers sulfate from shallow evaporative areas to deeper water where it is reduced to sulfide. Reduced nutrient input to oceans from land at many of the extinction intervals results from diminished silicate weathering and weakened delivery of iron via eolian dust. The falloff in iron-bearing dust leads to minimal nitrate production, weakening food webs and rendering faunas and floras more susceptible to extinction when stressed. Factors such as heat, anoxia, ocean acidification, hypercapnia, and hydrogen sulfide poisoning would significantly affect these biotas. Intervals of tectonic quiescence set up preconditions favoring extinctions. Reductions in chemical silicate weathering lead to carbon dioxide buildup, oxygen drawdown, nutrient depletion, wind and ocean current abatement, long-term global warming, and ocean acidification. The effects of extinction triggers such as large igneous provinces, bolide impacts, and episodes of sudden methane release are more potent against the backdrop of our proposed preconditions. Extinctions that have characteristics we call for in the thermal transgressions include the Early Cambrian Sinsk event, as well as extinction events at the Frasnian-Famennian, end-Devonian, end Permian, Early Toarcian, Cenomanian-Turonian, and end Cretaceous. The Late Paleocene and end Triassic extinctions are still under evaluation. The extinctions associated with the glacio-eustatic sea-level change in the Late Ordovician are not consistent with the conditions of our model.
DE: 1622 Earth system modeling (1225)
DE: 4912 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 1615, 4805)
DE: 4928 Global climate models (1626, 3337)
DE: 4930 Greenhouse gases
DE: 4962 Thermohaline
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting