DEATH BY HYDROGEN SULFIDE: A KILL MECHANISM FOR THE END-PERMIAN MASS EXTINCTION
We thus propose a modification of the anoxia mechanism, one that considers the possibility that the chemocline separating anoxic, sulfidic deep waters from the atmosphere, originally at the base of the wind-mixed layer of the ocean, collapsed catastrophically to the surface as sulfide levels built up in the deep ocean, especially if Late Permian oxygen levels were significantly lower than todays. We calculate the conditions under which such a collapse would occur, and the consequences for the resultant flux of H2S to the atmosphere. Widespread outcropping of sulfidic waters creates a flux to the atmosphere that quickly depletes the troposphere of hydroxyl radical, thereby allowing a hydrogen-sulfide rich plume to waft across the continents. In the Permian, such a cloud would poison terrestrial organisms in the way that aqueous H2S had already caused the demise of marine organisms. Biomarker data from Permian deep-sea sediments from Japan are evaluated in light of the predicted burst of productivity of photoautotrophic sulfur bacteria.