HR: 16:45h
AN: U24C-04    [Abstracts]
TI: Global Warmth and Nutrient Trapping Enhance End-Paleozoic Euxinia in an Earth System Model
AU: * Meyer, K M
EM: kmeyer@geosc.psu.edu
AF: Department of Geosciences, Pennsylvania State University, University Park, PA 16802, United States
AU: Kump, L R
EM: lkump@psu.edu
AF: Department of Geosciences, Pennsylvania State University, University Park, PA 16802, United States
AU: Ridgwell, A
EM: andy@seao2.org
AF: School of Geographical Sciences, University of Bristol, Bristol, BS8 1SS, United Kingdom
AB: The end-Permian mass extinction occurred during an interval characterized by global warmth and falling atmospheric oxygen levels. Although the cause of the extinction remains unresolved, geochemical evidence suggests that the event coincided with widespread anoxia and possible euxinia (anoxic and sulfidic waters). A combination of warm surface ocean temperatures, low atmospheric oxygen content, and high O₂ demand in the deep ocean likely induced anoxia. Anaerobic organic matter remineralization by bacterial sulfate reduction then produced euxinic conditions. Phosphate release from surface sediments and decreased phosphate burial under a sulfidic water column further enhanced oceanic euxinia through positive feedbacks to primary productivity. We hypothesize that late Paleozoic climate and geography favored marine euxinia, a potential kill mechanism for the extinction event. Here we use earth system modelling to explore the physical and biogeochemical conditions necessary for the development of intense euxinia during the end-Permian. We use the end-Permian configuration of GENIE (www.genie.ac.uk), an energy-moisture-balance atmospheric model coupled to a 3-D, non-eddy-resolving, frictional geostrophic model to investigate the transition to marine anoxia and euxinia in a greenhouse world. Equilibrium model simulations over a range of oceanic phosphate concentrations relate oceanic nutrient status to the buildup of euxinia and attendant hydrogen sulfide release to the atmosphere. Addition of a marine nitrogen cycle suggests that microbial denitrification reduces, but does not prevent H₂S buildup. Deep-ocean hydrogen sulfide appears with a doubling of phosphate, and localized photic zone euxinia develops with a tripling of phosphate. The greatest surface water H₂S concentrations are observed in upwelling zones and in the Paleo-Tethys Ocean, where nutrient trapping results in elevated phosphate concentrations. Significant hydrogen sulfide fluxes to the atmosphere result from extremely high nutrient conditions (6-10x modern phosphate). In this scenario, hydrogen sulfide in the ocean-atmosphere system would impose pervasive environmental stress that may promote extinctions both on land and in the ocean. These simulations support the hypothesis that extreme euxinia and episodic H₂S eruptions can occur in a nutrient-rich ocean, despite widespread denitrification under anoxic conditions. Spatially resolved predictions from this earth system modelling approach may guide further study of the rock record and help constrain the geochemistry of end-Permian mass extinction.
DE: 4802 Anoxic environments (0404, 1803, 4834, 4902)
DE: 4912 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 1615, 4805)
SC: Union [U]
MN: 2007 Fall Meeting