HYDROGEN SULFIDE RELEASE FROM THE END-PERMIAN OCEAN: A QUANTITATIVE EVALUATION

The cause of the end-Permian mass extinction, the largest extinction event of the Phanerozoic, remains controversial. The role of hydrogen sulfide poisoning has recently become of interest based on biomarker evidence for sulfide in the photic zone of the Permian ocean and biogeochemical calculations. In this scenario, low atmospheric oxygen concentrations, warm surface ocean temperatures and high O2 demand favored the establishment of euxinia. Catastrophic H2S release could occur if the upward flux of sulfide from deep-water exceeded the downward flux of oxygen into surface waters. The resulting migration of the chemocline to the air-sea interface would cause sulfide poisoning in both the marine and terrestrial realms. We used GENIE (www.genie.ac.uk), an energy-moisture-balance atmosphere model coupled to a 3-D, non-eddy-resolving, frictional geostrophic ocean model to evaluate this hypothesis. We performed a series of simulations designed to identify the conditions necessary for H2S outbursts and characterize the magnitude of the fluxes as a function of oceanic phosphate content. Significant ocean-atmosphere fluxes of H2S result from 6- to 10-fold increases in ocean phosphate at modern oxygen levels. These fluxes are focused in upwelling regions, although toxic H2S concentrations are also observed in the surface waters of nearshore equatorial regions. Our initial simulations support the hypothesis that episodic H2S eruptions can result from modest changes in the ocean's nutrient budget and may have contributed to the end-Permian mass extinction. Future work will investigate possible feedbacks involving sulfur utilization by sulfur-oxidizing phototrophs and the role of other nutrients (nitrogen).